Ruthless Pursuit of Power: Lucky Seven Edition
The Mystique of the Z/28's
7-Liter, 7000-RPM, LS7
by Hib Halverson, Content Director
Oops! Darn those pesky leaks!
Image: Various Web Locations.
In 2012, Camaro Nation got a nice
Christmas present when the "VIN Card" for 2014 leaked
out of GM. It listed "LS7", the seven-liter engine
formerly used in Corvette C6 Z06es, as a regular
production option for the Camaro in '14.
Of course, official GM denied the
leak was accurate. As Chevrolet's spokesperson for
everything Camaro, Monte Doran, told us right at the end
of 2012, "It is our policy to not discuss future
products, so I cannot comment on plans for the 2014
Camaro. I can tell you that a very early draft of our
2014 VIN card was leaked online. It was a preliminary
version that included both inaccurate and incomplete
Three months later, at the New York
Auto Show, Chevrolet announced a limited run of Camaro
Z/28s powered by LS7 427s.
2014 Camaro Z/28. Image: GM
This car ain't nothin' but a trackrat's hot rod. You'll get the 427, the Camaro
version of which is estimated to produce 500-horsepower,
six-speed manual, the iron-case drive axle, coolers, a
suspension more aggressive than a ZL1's along with the
carbon brakes once used on C6 Vette ZR1s and Z06/Z07s.
What you won't get is, also, interesting. These 427
Camaros are serious track cars with no acoustic
insulation or trunk carpet, no power seats, no HIDs, no
fog lamps, a single speaker sound system and optional
The Z/28's 500-hp surprise.
Image: GM Communications
The Milestone LS7
I think that big, thumping 427 is the
high water mark for Camaro engines. The ZL1 folks
probably wanna slap me silly for saying that, but, the
fact remains: LSA, for all its technology, still needs a
supercharger to make its 580 horses. Without boost, it
wouldn't get much beyond the LS3's 426.
About 150 of the LSA's 580-hp
come from this–GM's interpretation of the Eaton, R1900,
Twin-Vortices Series, Roots supercharger.
The 427 is an amazing piece of work:
fat torque curve, 500-hp, normally-aspirated, at
6300-RPM and a 7100 rev limit. There's really cool stuff
in that engine–titanium rods and intake valves, 11.0:1
compression, CNC-machined heads and a 7000-RPM
valvetrain. The LS7's specific output
(power÷displacement) is 1.18 and its power density
(power÷weight) is 1.12. At this writing, seven years
after the engine debuted in 2006, both are high marks
for a normally-aspirated, production V8 made in the
Western Hemisphere. Such performance makes for a
mystique about that unboosted, stump-pulling,
high-revving V8 which the supercharged 6.2 in the ZL1
lacks. So–while I appreciate the LSA, to me; LS7's case
is more compelling.
The obligatory, but always
stunning, Kimble cutaway shows the guts of a Corvette
LS7. The Camaro version looks the same except for having
black beauty covers and different exhaust manifolds.
Image: David Kimble for GM Powertrain.
GM Powertrain Division (GMPT) likely
objects to my "high water mark" statement citing the
specs of the direct-injected, 450-hp, 6.2L V8 which will
power the 2014 Corvette Stingray. No doubt, the "LT1",
the first example of the Fifth-Generation Small-Block
V8, is an outstanding technology showcase, but the fact
remains: a 427 in a production Camaro is a very rare,
it's only happened twice in the last 50 years. After the
2014 Z/28 build, you'll likely not see another unblown
V8 making more than 450-horses.
Set the Wayback Machine for 1969.
Some say, "History repeats itself."
The LS7 channeled a legendary engine of the past, the
ZL1, all-aluminum, 427 developed for the '69 Camaro.
Both are big-bore, pushrod V8s, influenced by
Chevrolet's efforts in motorsports. The ZL1 was a race
engine detuned and configured for street use. Some might
say the LS7 is similar: Corvette C5-R race engine
technology adapted to a production application with
compromises for drivability, emissions compliance and
When it comes to Chevy aluminum block
427s, how far has technology marched? A ZL1 made about
560-horses at 6800-RPM. When tested with 1960s
dynamometer procedures, the LS7 produces about
550-hp@6300 RPM, but has a fatter torque curve, weighs
less, has far lower exhaust emissions and gets much
better gas mileage. Further, it has better
reliability/durability, requires less maintenance and is
a lot nicer to drive. In today's money, a ZL1 cost about
thirty large. You can buy an LS7 for a little over half
that. The old ZL1 was installed in two Vettes, 69
Camaros and, later, sold over the counter, with
somewhere between 90 and 300 produced. To date, around
9000 LS7s have been hand-built at GM's Wixom, Michigan,
Performance Build Center (PBC). They've used in '06-'13
Vettes, sold as crate engines and, now, used in a
Camaro. Seems we've come far in nearly half-a-century.
The 1969 Camaro all-aluminum
Image: GM Powertrain.
The 2014 Camaro all-aluminum
Image: GM Powertrain.
LS7 History Book
Ok–reset the Wayback to the
early-'00s. In the American LeMans Series and at the 24
Hours of Le Mans, Corvette Racing had been eating
everyone's lunch. Its all-conquering C5-Rs were powered
by Katech-built, 427s. Based on production, LS1
architecture, they used a special cylinder block with
larger-than-stock bore and stroke, racing valve gear,
different cylinder heads, a motorsports-specific EFI and
an intake restrictor. Katech's C5-R 427s made about 600
horses at 6200-RPM.
Meanwhile, in the Summer of 2002,
over at GM Powertrain in Pontiac, where development of
production hardware took place, the Small Block team,
researching an LS6 successor, was experimenting with a
6.4-liter (390-cubic inch) V8 of about 450-hp. The 2005
Corvette was in development and they were looking at
this "six-four" as what might power the next Z06, due a
year later. During the design of the 6.4's cylinder
head, Katech's C5-R engines were an influence. The most
noticeable feature of this head was vastly different
intake port location and geometry, compared with the
"cathedral" intake port used in LS1, 2 and 6 heads. This
different intake port architecture would have
far-reaching effects on Small-Block V8s over the next
A Katech C5-R 427. Look at
all those carbon fiber parts on that engine. Fast as
hell and great eye candy. Image: GM Powertrain.
Corvettes dominated LeMans,
Sebring and Daytona during the C5 era. Under their hoods
was a 600+ horsepower 427. Shown is a C5-R in the esses
between the Dunlop Bridge and Tertre Rouge during the
2001 24 Hours of Le Mans. Image: Richard Prince.
John Rydzewski, currently Assistant
Chief Engineer for Passenger Car Small-Block V8
Engines, said in a 2008 interview about that head, "A
key enabler of this was moving the pushrod over. Now we
had a bigger space, so we moved the port up, gave it a
straight-on approach, made it larger, wider, with less
turns and less bosses in the way of the flow path. The
result is a huge improvement in performance."
Six-four development progressed into
the Fall of 2002, but there was growing skepticism about
displacement. Some were thinking that closer to
seven-liters might be necessary. Elsewhere in GMPT,
people were doing computer analysis of what it might
take to reach the 500-horsepower level and that pointed
at 7.0L, too.
Dave Muscaro, who, six months later,
would be appointed as Assistant Chief Engineer Passenger
Car V8s, told us about that period. "From a 6.4L vs
7.0L perspective, the goal of making 500 hp came
sometime before I joined the program. I have a
file showing analysis work to probe this power level was
done at the end of October 2002. The analysis work was
simply to see what airflow, friction, induction and
exhaust restrictions, compression ratio, etc, etc, would
be needed to create 500 hp. At that time, it was
recognized that the engine displacement would likely
need to go to 7.0L.
The first time the CAC
visited with John Rydzewski, the subject was the LS3 and
the cylinder head it used which was derived from the
still-born six-four. Image: Author.
Winter of 2002/2003. Six-four
development was well into the hardware stage. GM Vice
Chairman for Global Product Development, Bob Lutz, along
with senior Powertrain executives, then GM Powertrain
Group Vice President, Tom Stephens, and then Small-Block
Chief Engineer, Sam Winegarden, upset the apple cart by
deciding the first number in the C6 Z06's power rating
must be a "5". While this decision is a well-known part
of LS7 history which added to its mystique, it would be
ridiculous to assume that, one Friday after work, Bob,
Tom and Sam, got together for beer and burgers then
wrote "500-hp" on a bar napkin. More likely is that Mr.
Lutz,, Mr. Stephens and Mr. Winegarden reviewed some of
the analysis data Muscaro cites, considered where their
V8 engine technology was then and where they wanted
Corvette to be power-wise in the next five years, then
set 500 horses has a goal for their engineers.
"Competitive Pressure was part of
it. The Viper was one of the competitors out
there–probably the biggest–and there were others,"
John Rydzewski, who took over as ACE from Muscaro in May
of 2005, told us in a second, 2012 interview.
A decade ago, the most powerful
Corvette engine, the LS6, made 405-hp but the Vette's
underhood competition–most high-profile of which was the
Dodge Viper's monster (but, also, inefficient) 488-cubic
inch, 500-hp V10–was putting the Corvette's power rating
to shame. There were others, too: Porsche
Turbo-444-horses, Mercedes-Benz SL55 AMG-476-hp and
Ferrari 575M Maranello-508-hp.
A 500-hp Corvette? Well...duh.
As Corvette Executive Chief Engineer,
Tadge Juechter, who, during the C6 Z06 development, was
Assistant Chief under David Hill, explained, "The LS7
is the pure-blood, track engine. When we were developing
it, we knew it was going to be normally aspirated. For a
while, that engine was going to displace 6.4-liters and
the first horsepower target was 450. The base engine was
400. We thought: Oh man, more than 10%–that'd be a nice
bump. Remember, with the previous Z06, we were, first,
at 385, then 405, so that (50 more horsepower)
was our mindset as a good performance delta.
Corvette Executive Chief
Engineer, Tadge Juechter discusses the
LS7 with the Camaro Homepage.
"The horsepower wars were on and,
as we developed (the six-four), we saw these new
entries coming out with higher horsepower. We had senior
leadership–Lutz, Stephens and others–saying, 'The first
number's gotta start with a '5'. At the working level,
we wanted to get as much as we could. Powertrain didn't
know if they could get to 500. There was a lot of
pressure from the higher-ups saying, 'We think you can
do it. Let's put that stretch target out there and let's
see if you can get there.' They just said, 'Well, the
original target was 450 and we're going to see what we
About the same time, another decree
came from then Chief Hill, himself, who mandated the
2006 Z06 accelerate from 0-60 in less than four-seconds.
The only way to do that with the car's weight and 3.42
axle ratio was to stay in first gear, so–this 500-hp
engine would, also, be a 7000 RPM engine. It's easy to
understand Hill's quest–power to keep the Z06 a player
in its market segment into the next decade. At this
writing, nine years later, Hill's goal was achieved–by a
By late Spring, 2003, the six-four
was deemed incapable of 500-hp or 7000 RPM, so with
newly appointed ACE Muscaro at the helm, the Powertrain
folks working on the LS7 hit "reset" and began
developing a new and even bigger engine. With the
displacement now set at 7-liters, what Katech had been
doing with its C5-R engines was even more influential on
the Small-Block team at GM Powertrain.
"As to when we 'officially'
switched to a 7.0L? That would be hard to pinpoint,"
Dave Muscaro continued. "Before we 'switch' program
direction, we do analysis and then test a 'mule engine'
to prove our analysis. At the time I came in, we did not
have any 7.0L engines, although a couple were ordered
from Katech in November 2002. These engines did not yet
exist, but the parts to build them were being
contemplated and decided upon. So, when I came on the
scene, one of the first things I did was sit down with
Katech and devise a development plan to build some
engines and start proving our ideas on how to make a
500-hp 7.0L. At this time, there may have been one or
two 6.4L engines still running, but I was not much
interested in trying to make the smaller engine work for
a 500hp target. I do not recall any 'official' date when
we decided upon a 7.0L displacement. Since we were short
on power right out of the chute with a 7.0L, you can bet
I didn't go back and try a smaller engine! So by
default, a 7.0L was what it would become."
Katech's Kevin Pranger, who
was the "engine guy" for the C5-R and the 7-liter part
of the C6.R program. Image: Author.
Kevin Pranger, who was Katech's
manager for the C5-R engine program, was, also,
interviewed for this article. He described Katech's
first efforts at a 7-liter race engine and Powertrain's
interest. "We started putting liners in LS1 blocks.
Then, GM cast us up a couple of special blocks with
thicker aluminum so we could use thick wall liners with
a larger bore," Pranger told the CAC. "Those
castings allowed us to do some testing. From that, we
were able to come up a 4 1/8th bore and a four-inch
stroke to make seven-liters. That's when GM decided to
build an official, 4 1/8th bore 'C5-R Block'. They were
able to amortize the tooling for the race program by
selling the block in the (GM Performance Parts)
"They (Small-Block engineers)
started coming over here, looking at what we were doing
with the cylinder heads and the block," Pranger
continued. "They got a lot of ideas from that. The
LS7 head looks a lot like the original C5-R, '005'
castings. I think a lot of the LS7 was modeled after
what we were doing with the C5-R."
Tadge Juechter expanded upon Kevin
Pranger's perspective, "You talk about 'technology
transfer' from the race program to the street program?
LS7 is a perfect example. Some of the
rank-and-file Powertrain engineers weren't accustomed to
working on an engine like this, so we actually did get
help from Katech and others who'd done race engines who
helped with the porting design and other things. There
were so many different ideas tried and so many blind
alleys traveled down. It was an eye-opening experience.
Developing that much power with normal aspiration and
meeting emissions standards of today is something
special. A lot of the lessons learned can be applied to
Which they were, as we will see
"Significant change was needed to
increase engine throughput." John Rydzewski stated
about the engine's displacement. "Increasing bore and
stroke were enablers for the increased performance. Some
of the executive leadership desired a displacement such
as the iconic, 427 cubic inches. Our analytical and
geometric studies supported the 104.775-mm
(4.125-in) bore and 101.6-mm (4.0-in) stroke
(7.008-liters or 427.484 cubic inches). They were
selected for the LS7 program."
Ya think some of John's "executive
leadership" had been waxing nostalgic about 427 Vettes?
Having dreams of four-inch-plus pistons and
two-inch-plus intake valves? Hearing the seductive sound
of a high RPM valvetrain motion? Feeling the thump of a
big-inch motor pulling hard in the low-mid-range?
Listening to the lopey idle of a big cam? Yeah–that's
what those car-guy, true-believers were doing. Thank the
car gods there were a few of them left.
In 2012, we met with John Rydzewski, again, with the subject this time being the
LS7. Image: Author.
The folks who did the
six-four head eventually saw the fruits of their labor
on the LS3 under the hood of the '08 Corvette and the
2010 Camaro SS. The '09 ZR-1 and the 2012 ZL1 used
nearly the same head, but it was made of a more robust
aluminum alloy using a slightly different casting
process. From an airflow perspective, the only
difference was the supercharged head's intake port
Image: GM Powertrain.
And what of the six-four? Well–it was
never considered for production–never made it into a
car, in fact, but its development was not for naught.
Six years later, the 6.4's head appeared on the Camaro
SS's LS3 and L99 and, in 2012, after a slight revision
in intake port design along with a change in material
and foundry process, it, also, became the cylinder head
used on the ZL1's, 6.2-liter supercharged LSA, but
Five hundred horsepower from a
normally-aspirated V8 while meeting emissions and fuel
economy standards was a tall order in late Spring 2003,
when full-scale LS7 development began. Muscaro's Small
Block Team was soon burning the midnight oil in a
ruthless pursuit of power with a 500-horse, 7000-RPM,
emissions-legal, no-guzzler, 427 as its objective.
Actually, perhaps as many kilowatt
hours were burned as "midnight oil". General Motors has
significant computer modeling and simulation resources.
Computer software tools such as "Finite Element
Analysis" (FEA), "Uni-Graphics" and "Computational Fluid
Dynamics (CFD) were used during design and development.
A different block casting and a new head were in the
program even before the computers got warmed-up. Other
key features of the engine were determined by computer
modeling–a forged steel crankshaft, pressed in, rather
than cast-in-place, liners and titanium connecting rods
were, also, deemed necessary through modeling.
Back in '12, we also met with
Sam Winegarden, the top engine guy at General Motors. He
told us the LS7 has always been one of his favorite
projects. He also gave us some inside views of what it
was like when he was the Small Block Chief and LS7 was
under development. Sam's story about computer modeling
of combustion was a revealing insight to how quickly
computers have compressed product development time.
The LS7 was developed on Sam
Winegarden's watch as Small-Block Chief Engineer, He
tells a great story about computer modeling. "I was
still Small-Block Chief, the first time these guys could
model combustion. This would have been back in about '03
or '04. Dr. Gary Mendruziac (formerly with GM
Advanced Research) started us down this journey and I
always remember this. It took him one week to do the
model for the induction stroke. Second week, he did the
compression stroke. Third week he burned it. The fourth
week was the exhaust stroke–a month of computer time to
model one cycle. "Now, I can do that in a matter of a
few hours. Just to give you an idea for how much faster
the computers have gotten in that length of time. Eight
years and we've gone two orders of magnitude faster."
GM spent a couple of months on LS7
computer work before the first LS7s were assembled by
Katech in the Summer of 2003. Shortly after that, more
early development engines were done by Powertrain's
experimental engine assemblers in Pontiac. Starting on
24 February 2004, development engines were built at the
Performance Build Center.
Special Block and Crank
GM's production, aluminum V8 bare
blocks, or "cylinder cases" are cast by Nemak, a
world-class foundry in Monterrey, Mexico, which supplies
engine manufacturers world-wide. The LS7 case shares
qualities Gen 3/4 engines have had since their 1997
debut: deep-skirted, 319-T5 aluminum block, long head
bolts threading deep into its main bearing webs,
six-bolt main bearing caps, a center thrust bearing and
gray iron liners which are centrifugally-cast for
increased density to enhance strength and allow thinner
cylinder walls. All this makes a lightweight, rigid,
block structure offering good durability and reduced
friction–all important basics for a specialized engine
like the LS7.
The structure of the LS7
basic engine is a specific aluminum cylinder case.
Image: GM Powertrain.
While the case is a Gen 4, it's a little different from
its6.2-liter siblings used in other Camaros. It has pressed-in, rather than
cast-in-place liners and its water jackets had to be
altered to accommodate them. The LS7's bore, 104.775-mm,
3.18-mm larger than that of the existing LS2, was
greater than cast-in place liners would tolerate and
still have adequate cylinder wall thickness, but it
works if partially-siamesed, pressed-in liners are used.
The liners, also, extend farther into the crankcase than
do the cast in-place units. Because of the the LS7's,
long stroke, the extra length is necessary as a guide
and support for the thrust side of the piston skirt.
John Rydzewski told us that, after
casting, LS7 blocks are shipped to a Linamar Corporation
facility in Guelph, Ontario, Canada for rough machining,
installation of the pressed-in liners, and finish
machining operations. One of those operations, machining
"hone over-travel clearance", became a major issue
during the engine's late development stage. "When the
block is honed, the bottom of the honing tool needs
clearance so it doesn't contact the block below the
bore," John Rydzewski stated. "Before the honing
operation, the block is machined in that area to provide
clearance. The resulting surface geometry has a big
impact on the block structure. Hone over-travel
clearance used to be machined (LS1, -2, -6 and early
LS7 development cases) with a 3-mm radius. To get
more strength in that area, we eventually changed to a
more gentle, 8-mm radius. That was a big durability
enabler at the LS7's power level."
The pressed-in liners are siamesed for about a two inch section where two liners
would interfere. There's no decrease in wall strength
because the flat surfaces of the two liners support each
Image: Mark Kelly/GM Powertrain.
As the pistons move up and down in
their cylinders, they force air in and out of the spaces
(or “bays”) beneath them. At high RPM, these flow
reversals are rapid, violent and really whip up the oil
as well as creating power loss. One way to mitigate this
problem is to vent each bay to its neighboring bays.
Like other Gen 3 and 4 blocks, production LS7 blocks
have openings or "windows" their main bearing webs
between bays for this “bay-to-bay breathing". Rydzewski
went on to say, "Hone over travel machining, affects
the size of the resulting windows in those bulkheads
which are very significant to bay-to-bay breathing and
In its ruthless pursuit of power, GM
didn't just haphazardly put holes in the main webs. In
fact, early development LS7 cases did not have windows
at all because, initially, GM didn't know how to produce
a block with both bay-to-bay breathing windows and
reliability at 500-horsepower. Extensive finite element
analysis along with thrashing engines to death–in some
cases, literally–on the dyno and in prototype Vettes,
eventually resulted in the LS7 block having both the
necessary bay-to-bay breathing windows and more overall
strength than any of its predecessors.
The backside of one of the
bay-to-bay breathing windows in an LS7 case.
Besides 8-mm hone over travel radii,
other changes were made to increase the block's strength
for use at the 500-hp level. First, the material used in
the main bearing caps was upgraded from forged powdered
metal to 1141 steel machined from forged billets.
Secondly, each cap is located with by dowels making a
more rigid structure once all six bolts are tightened.
Some of Linamar's block machining
processes are unique to the LS7, but the final two are
noteworthy in that they came directly from racing. While
they are standard procedure at places like Katech, they
are rare for a production engine. First, all LS7 cases
are align-bored with deck plates installed and the head
bolts tightened to specification. Second, all LS7 blocks
have their liners honed with the same deck plates
installed and head bolts tight.
Once Linamar finishes LS7 blocks,
they are cleaned and shipped to the Performance Build
Center for assembly. We visited the "PBC". in the Winter
of 2012 to assemble an LS7
and while there, we learned there is no pre-assembly
parts cleaning at the PBC. When Linamar cleans a block,
they are spotless. Other suppliers are, also, required
to furnish parts which are clean and ready for assembly.
We asked Rob Nichols, the facility's Engineering
Supervisor, how they ensure that. "We visually check
all parts and if they are not to our liking, we send
them back," Nichols told the CAC. "Periodically,
we test-wash blocks and crankshafts. Any contaminants
fall into a filter we place at the bottom of a wash
basin," Nichols told the CAC. "The weight of
these filters is pre-measured. We take the filters and
sediment and bake them in an oven to dry out the filter
and debris. Then, we reweigh the combination. The
difference between the base weight and the weight of the
filter with debris gives us the amount of sediment
washed off of the parts. We have tolerances for the
amount allowed. If it falls out of spec, we alert the
supplier and (do further testing to) make sure
all incoming product is conforming."
LS7 main bearings being
installed at the PBC. Mark Kelly/GM Powertrain.
The LS7 was the first production
engine to use "increased-eccentricity" main and
connecting rod bearings. The term refers to the
thickness of the bearing. Eccentric bearings get
slightly more thin from the center to the edge where the
split line relief starts. The difference in this
thickness is the "eccentricity". Mark Damico, Design
System Engineer–Small-Block Base Engine, who has worked
on the Gen 3/4/5 engine program since 1993, told us
that, prior to the LS7, bearings were either the same
thickness from the center to edge or they had a very
slight eccentricity. LS7 bearings have much more
eccentricity, .0006-in for the number 1, 2, 4 and 5
mains and a whopping .0011-in for the rods. This higher
level of eccentricity improved durability because
bearings of this design flow more oil and are more
tolerant of bearing bore distortion which increases with
cylinder pressure. Use of high-eccentricity bearings
eventually expanded to other Corvette engines, the LS9
in 2009 and LS3 dry-sump in 2010 along with the Camaro's
LSA in 2012.
If there's a downside of
high-eccentricity bearings it's that clearance
checking in the field is a little more
complicated in that care must be taken to
always check the clearance at about 90° to
the bearing part line. Also, parts choices when
bearings are replaced can be critical. If
aftermarket bearings are chosen they must
have a level of eccentricity that is similar to
that of OE bearings because–if the bearings have
less eccentricity–the engine will have either
insufficient oil flow in bearings or–if the
bearings have more eccentricity–insufficient oil
An LS7 rod bearing with its
obvious red, polymer coating. In a short period after
the first engine start, some of the red wears away
leaving the anti-friction polymer coating to fill the
microscopic voids in the surface of the aluminum. Image:
Until the 2012 model year, bearings
of traditional, "tri-metal" (steel backing, bronze
second layer and a top layer of lead) construction
were used in the LS7's #1, 2, 4 and 5 main bearing
positions and in the connecting rods. European Union
legislation enacted in 2011 prohibits the import of
products containing lead, so the main and con rod
bearing designs were changed. Lead was replaced with
a synthetic polymer making a "bi-metal-with-polymer"
design. The center (#3) main bearing remains
aluminum on a steel backing. According to Mark
Damico, because of the firing order used on all Gen
3, 4 and 5 V8s, the second and fourth main bearings
are subjected to the highest loads. After a long
period in service, if an LS7's bearings are going to
wear, it'll be the #2 and #4 mains which show it,
first. The two end bearings may see a lesser level
of wear due to (#1) the accessory drive or (#5) the
flywheel. The center main experiences the least
vertical load and while it is an
increased-eccentricity design, it's never required a
lead overlay nor polymer coating.
An early style, 4140 forged
steel, LS7 crankshaft. Image: GM Powertrain.
Rolled fillets at the edges
of each each bearing journal improve the strength of the
crankshaft. All but the front main journals are hollow
to both reduce mass and facilitate bay-to-bay breathing.
Tungsten, a heavy metal, is used to balance the end two
counterweights. Image: GM Powertrain.
An LS7 engine part which I think is
so pretty is the crankshaft. With its appealing
brownish-coppery color and intricate finish
machining–darn it–it's just too cool-looking to be in an
engine. The eye candy that they are, LS7 cranks are
pretty trick parts for a production application being
micro-alloy steel forgings manufactured by specialty
supplier, SMI Crankshaft in Fostoria, Ohio. The cranks
have some journals which are hollow for less mass and,
in the case of main bearing journals, improved
bay-to-bay breathing. All the journals have rolled
fillets for increased durability and, like race engines,
the front and rear counterweights are balanced with
"heavy metal" slugs made of tungsten. Early LS7 cranks
were 4140 steel. Later LS7 cranks, including all the
Camaro units are 44MNSIVS steel. "The reason we
switched," John Rydzewski told us, "was it
eliminated one of the processes in fabricating it. With
4140, you have to quench and temper the crankshaft
before final machining. With this new material, you
don't have to quench and temper because (the steel)
has a different grain structure. The end result is the
same properties but (using the new material)
eliminates a step reducing the cost of
Under the watchful eye of PBC Assembler,
Mike Priest (left),
the author installs a late-style LS7,
44MNSIVS forged steel crankshaft.
Mark Kelly/GM Powertrain.
Featherweight Engine Artwork
Part of the LS7's mystique is its use
of titanium. Its connecting rods and intake valves are a
rare application of that lightweight material in a
To get the LS7 to reliably
turn 7100 RPM, lightweight titanium rods and intake
valves were required. Image: Author.
Titanium is a silver-gray metal. The
ninth most abundant metal, it's often found in mineral
deposits and small amounts are in most living things.
Number 22, on the periodic table, engineers often refer
to it by its chemical abbreviation "Ti" (pronounced
"tie"). Titanium's density is somewhere between that of
aluminum and stainless steel. As strong as some steels,
but 45% lighter, It has the highest strength-to-mass
ratio of any metal. Its other noted property is
excellent resistance to corrosion. It is slow to react
with water and air because it forms its own, oxide
coating which protects it from further reaction. Ti is
fairly hard, non-magnetic and does not conduct heat or
electricity very well. Interestingly, besides aerospace,
military and industrial applications–and LS7 engine
parts–titanium is a popular metal for jewelry. Before I
got married, my then-fiancée asked me what kind of
wedding ring I wanted. "Titanium, because of its
strength-to-mass ratio my dear."
Making Ti engine parts isn't easy.
While the metal is abundant, it rarely occurs in pure
form. Typically, it's produced using the "Kroll
Process", a complicated and quite costly
procedure. In a series of high-temperature chemical
titanium "sponge" is extracted from rutile, a common
mineral.. Next, Ti sponge is melted into ingots.
Since titanium ignites before its melting point is
reached, this is done in a vacuum or an inert
atmosphere–other than nitrogen, of course, because Ti is
one of the few elements which burns in pure nitrogen.
The Vacuum Arc Remelt (VAR) process produces titanium
ingots which are then rolled into flat or bar stock then
forged into LS7 rods and intake valves. Machining
titanium can be difficult, because it galls or softens
if improper tooling or inadequate cooling is used, i.e.:
if you screw-up the machining process, a lot of
expensive raw material ends up scrap. How expensive? At
this writing, titanium ingots run about $10.30 a pound.
For comparison, aluminum was about 93 cents a pound and
benchmark, cold-rolled steel was about 37 cents a pound.
The LS7's forged titanium con rod is
a work-of-art in many ways. Visually, it's so pretty
that, if they weren't so expensive, people would buy
them as intriguing Christmas tree ornaments,
attention-getting paper weights, unusual props for
jugglers or for "industrial-chic" themed interior
decorating. Ok, seriously–the Ti connecting rod is
pretty because of the silvery-gold-colored,
chrome-nitride (CrN) coating typical of titanium engine
It's, also, a work of "engine-development-art" as it
took a lot of computer analysis and engine testing to
get it to where it could be reliable and durable to the
standards GM has for all production engines.
The LS3 rod on the scale
weighs in at 22.74-oz. The LS7 Ti rod in the foreground
weighs 16.38-oz., 28% less. Image: Author.
Why a Ti rod? Not for the reasons
most might think. Indeed, substituting forged titanium
for forged steel significantly reduces mass allowing the
rotating assembly to accelerate quicker improving the
engine's response and reducing parasitic losses as the
engine speed accelerates, however, titanium LS7 rods are
more a durability measure than a performance
On the power stroke, when the piston
and rod assembly reach the bottom of their travel,
inertia combined with what's left of combustion pressure
apply a great deal of load on the oil film between the
upper bearing shell and the crankshaft journal. During
LS7 computer modeling, the Small-Block team discovered
that with the, Group III, 5W30 synthetic engine oil used
in Corvette engines, connecting rod bearing oil film
strength would be unacceptable when the engine was under
the heaviest load and at high RPM. Further, they decided
a titanium rod would provide the mass reduction
necessary to decrease those inertia loads such they
would not exceed the film strength of the oil.
"During development of the
6.4-liter, we didn't use a ti con rod," John
Rydzewski said. "It was an investment-cast (steel)
con rod. It had a lot of mass lightener pockets–less
material (than a forged LS6 rod) to keep the mass down.
However, with the seven-liter, the longer stroke and
higher engine RPM was a concern for proper oil film
During one of the CHpg's LS7
interview sessions, Asst. Chief Engineer, Rydzewski
discussed the LS7's titanium rod. GM Powertrain's
Communications Manager, Tom Read looks on. Image:
"Our analysis capability is really
good for oil film thickness. This analysis comprehends
engine speeds, loads, temperature, mass/inertia and
geometry. At high speed, you have a lot of inertia, a
lot of reciprocating mass which will reduce oil film
thickness. We had to make a big move to increase the
film thickness robustness. That (a titanium rod) was the
most straight forward way to do it."
That begs the question: rather than
an expensive set of Ti rods, why not just a better
engine oil? You can buy a lot of premium, ester-based,
10W30 synthetic oil, which has better film-strength
properties, for the cost of those rods.
Well...it's just not that simple. To
use forged steel rods and a higher film-strength oil,
General Motors would, first, have to admit that fabled
Mobil 1 5W30 and its "Dexos 1" successor, were
inadequate for use in the LS7. That was so
not-gonna-happen. Plus–while it is true that there are
engine oil products with better film strength properties
than the factory-fill 5W30 used in LS7s; when we asked
John Rydzewski about that, he commented, "A higher
weight oil can improve film thickness, but that, alone,
would not have met the design requirements." So,
the LS7 has those bitchen ti rods, with their durability
advantages and the better throttle response they
provide, to add to its mystique.
Rydzewski continued, "Titanium
rods are good for reducing reciprocating mass but their
downsides are: they are expensive, (Note: we
couldn't get cost numbers from GM but, according to Stan
Lorence, Parts Manager at Tom Henry Chevrolet in
Bakerstown PA, a replacement
LS7 titanium rod is nearly four times the price of a
steel, LS3 rod). They take a lot of machining steps.
They come from Mahle in Germany, so there is a long
lead-time. The process–forging, a lot of machining and
application of the (chromium nitride) coating–is
complicated. There are few suppliers out there which can
do titanium rods for production applications.
"We've had pretty good luck with
them. We've never broken a rod because of the strength.
An unusual property of a titanium rod (compared to a
steel rod) is its different modulus of elasticity.
They bend a little bit differently and that concerned us
at first. Because of the different modulus of Ti, the
stiffness requirements had to be comprehended in the
design. Many sections of the Ti rod were larger than
required for a con rod made of conventional (forged
"Also, we had issues with 'Ti dust
wear' during our first round of builds. And then we
started seeing some signs later on, once we got into
parts that came off manufacturing equipment. The two
rods (on the same crankshaft journal) rub against
each other. Titanium on titanium does not wear well. If
you have sharp corners, particles can break off. They
get between the rods and start wearing away the coating
and get you into trouble."
The arrow points to the
groove or divot which was added to LS7 rods to combat Ti
dust. Image: Author.
Ti dust forced implementation of
special manufacturing procedures at Mahle. At the part
line between the rod and cap, there can be slight
misalignment resulting in a sharp edge which can abrade
the adjacent rod. The ti dust problem was traced to that
area. For engines built for the second phase of
development, a small groove was added on the sides of
the rod's big end right at the parting line which
eliminated the possibility of any sharp edges. Besides
Ti dust control, during the LS7 development, other
procedures were introduced to avoid impact damage to the
rod which causes stress risers and damages the coating.
In a departure from what most people,
including some veteran mechanical engineers, would
expect, the LS7 engine does not use a forged aluminum
piston. It uses a cast, eutectic aluminum piston, but
that's greatly simplifying the issue as there's quite a
story to the LS7 piston. "They started out with
forged on the six-four." John Rydzewski told the
CHpg. "When they picked a (piston) supplier
for the seven-liter, it was Mahle which came back and
said, 'We can do this in a cast piston. We've got the
knowledge and it will work.' The decision was to proceed
with a cast piston. It met all the requirements–met the
specifications and it was less expensive."
In February of 2012, we visited
Katech to learn more about its role in helping GM bring
the LS7 to market and cast piston was an issue we
covered. "One of the big challenges with a cast
piston was durability at 7000 RPM," Katech's CEO,
Fritz Kayl, told us. "We did stuff later in the
program on that. We met the power targets pretty easy
but the durability side was more of a problem. The big
challenges were piston speed and how to reduce parasitic
"With a four-inch stroke, you have
tremendous piston speed. I'll give credit to GM–they set
that (cast piston) as a challenge and they were
not going to give-up on it. Certainly we didn't have
that technology here. Everything we do in racing is
forged pistons, but with the LS7, forged pistons were
off the table.
|Katech's Fritz Kahl explained
piston speed to us in an interview at his Clinton
Township, MI facility. While the LS7s piston speed is
only 200 feet/min. higher than that of the C5-R race
engine, inertia loading on the pin and pin bosses
increases with the square of the speed and the LS7 uses
cast pistons while the C5-R engine used forged. Image:
"At that time, piston speed for
racing (C5-R forged piston) was about 4500
feet-per-minute but 7100-RPM for a Corvette LS7 is 4700
feet-per-minute. (LS2 and LS3 cast piston speeds
max'ed at 4000-fpm.) And of course, bearing loads and
everything else goes up with (the square of)
piston speed. That's why the concern. They had some
problems with pistons in the early going but they got it
solved. As it turned-out, they (GM and Mahle)
were right. Those pistons are durable.
So, how did Mahle pull off an
advancement some thought impossible? By combining a
special aluminum alloy with a new casting method, more
robust heat treating and new developments in piston
The LS7 piston is cast from a
eutectic aluminum/silicon alloy having small amounts of
copper and nickel. This alloy, "Mahle 142," was first
used for pistons in the LS6 engine of 2001. "M142"
offers increased strength and less expansion at high
temperature providing better control of piston-to-bore
clearance, both at the skirt and the ring lands. That
improved dimensional stability reduces piston noise,
improves oil control and enhances durability.
In an interview, Aaron Dick, the
Application Manager assigned to the LS7 piston
development at Mahle, told the CAC, "We did (a
cast piston) primarily for weight-reduction. A
requirement was very lightweight reciprocating masses.
Taking that challenge, we looked at a new, patented
casting process we had. We were able to cast the piston
lighter than we could make a forging."
Mahle developed the "Ecoform" casting
process in the early-'00s as a mass reduction strategy
and LS7 was one of its first applications. This casting
technology creates recesses, or cavities, in the ring
belt which could not exist in a forging. The resulting
high-strength, reduced-mass, cast piston was cutting
edge technology for high-volume, production engines in
This cutaway Mahle Ecoform
piston, while not an LS7 unit, is typical of pistons
made with that process. It is very light because of
cavities the process forms in the underside of the
piston which could not exist in a forging. Image: Mahle.
The heat treat specification for the
LS7 piston is, also, a departure from the norm and
intended to improve strength. "The vast majority of
gasoline pistons have a T5 heat treat where the LS7 has
a T7 heat treatment," Dick continued. "That
increases the strength and the hardness of the piston
and that adds strength at the pin bosses–the lower
temperature parts of the piston. At high temperatures,
the heat treatment is not as critical. In the piston
crown, for example, it's not helping as much, but in the
lower end of the piston, the T7 heat treat improves the
properties of the material. This helps when you have
'inertia loads'–high speed but no load. For
example: if you downshifted going into a corner, when
the engine revs up, (inertia loads) are trying to
rip the piston pin out of the piston."
The LS7 piston has "asymmetric"
skirts with the major thrust face being wider than the
minor face, a configuration responsible for another
slight mass decrease. The skirts are coated with
"Grafal", Mahle's proprietary, polymer coating which
reduces friction, increases scuffing resistance and
allows less piston-to-bore clearance leading to less
The underside of an LS7
piston and its wrist pin are both engineered for reduced
mass. Image: Author
An LS7 piston pin, or "wrist
pin"–arguably one of the most highly stressed parts in a
high-performance engine–is made of a gas-nitrided,
chromium-molybdenum-vanadium steel meeting the 31CrMoV9
specification. This is a more robust material than
normally used in GM V8 pistons. it allowed the wall
thickness of the pin to be less and the inside diameter
to be tapered to reduce mass but still enabled the pin
to meet GM's abusive fatigue life tests. The piston is
phosphate-coated, the main purpose of which is to
improve the reliability of the pin bores during the
break-in period. The pin locks are circlips, but they're
made with 1.8-mm rather than 1.6-mm wire to increase the
circlip's tension. During development, according to then
Small-Block Chief, Sam Winegarden, the LS7 engineers
learned that, at high RPM, the loads on the 1.6-mm
circlip at top-dead-center and bottom-dead-center can
deform it and pop it right out of the pin lock groove.
Going to the more robust circlip solved that problem.
More "light-weighting" comes
with the LS7 piston's skirt asymmetry. Image: Author.
Areas immediately adjacent
to the top ring groove are hard anodized
and the surfaces of the piston skirts
are coated with Grafal, a
polymer-based antifriction material pioneered by Mahle
with the 2002 LS6 piston. Image: Author.
Again, looking at the
underside of the piston, to increase strength, the top
portion of the wrist pin bore bosses, indicated by the
shorter arrows, are wider than the bottom portion.
Additional mass reduction comes in
shortening the piston pin, but to do that and preserve
the ability of the pin bosses to carry the load, the pin
bores were moved closer together and the tops of the pin
bores curve inward to further strengthen that area. To
clear those parts of the pin bores, the small end of the
connecting rod is formed with a pronounced step with the
top being more narrow. Another reason for a shorter pin?
It provides clearance between the crankshaft reluctor
wheel and number eight piston.
An '06-'11 Corvette LS7
piston/rod assembly. The Camaro unit is identical except
for a polymer-coated, bi-metal rod bearing. The four
valve reliefs are a welcome feature of the piston top
for those wanting to go to an aftermarket cam profile.
Image: GM Powertrain.
The piston top has four valve reliefs
which, according to Aaron Dick, are not necessary with
the stock LS7's valve lift. They exist because, after
the design was finalized, GM wanted slightly less
compression, so four valve reliefs were added. An
unintended, but sometimes welcome consequence, is that
these reliefs provide adequate valve-to-piston clearance
for some aftermarket camshafts, such as Katech's
"Torquer" series of LS7 cams, having more aggressive
profiles without having to change pistons. The ring
grooves are machined with a slight upward tilt which
counteracts the rings' tendency to flex downward under
operating pressures and temperatures. The top ring land
is hard anodized to prevent microwelding on the flanks
of the ring groove.
The top ring is filled with
moly as an antifriction measure. The LS7's Napier second
ring was developed for the 2002 LS6 and later used on
all Small-Blocks. A "Napier ring" has a distinct shape
that enhances oil control by scraping oil off the
cylinder walls as the piston moves down in the bore.
The LS7 ring package starts with a
1.2-mm, moly-filled, steel top ring. It is "coined" to
give it an upward twist which flattens under combustion
pressure improving ring seal. The second ring is, also,
1.2-mm, but is made of ductile-iron and has a
Napier-face for enhanced oil control. The oil ring is a
2-mm, 3-piece unit consisting of two gas-nitrided rails
and an expander.
Most of this cutting-edge piston
technology is aimed at reducing mass but, also,
increasing durability. Aaron Dick's closing statement
says it all about the level of technical sophistication
in the piston assembly: "it's a very,
highly-engineered piece for a specialized application."
During engine assembly,
techniques similar to those used in the engine shops at
Katech or Hendrick Motorsports are used to install the
pistons, including an awesome ring compressor which the
author insists would look excellent in his tool box.
Image: Mark Kelly/GM Powertrain.
The performance requirements Dave
Hill's Corvette Team gave the folks at Powertrain were
demanding: 500-hp, 7000 RPM and engine reliability under
levels of acceleration, braking and cornering forces
unattained by previous stock Corvettes. Computer
modeling quickly demonstrated that, to meet those
requirements, the Z06's wet sump oiling days were over.
Even the best of GM's wet sumps, the fabled "bat-wing"
oil pan of the C5 days, could not be relied upon for
consistent oil flow at the LS7's lofty RPM range and at
the Z06's gut-wrenching handling limits, so LS7 became
the first production GM engine to use a dry sump oiling
Mocked up in the photo
studio, the 2010-2014-spec., LS7, dry sump components.
Image: GM Powertrain.
"Our biggest surprise was
Powertrain's choice of a dry sump." Katech's Fritz
Kayl told us. "In the early parts of the program, we
were able to show them what performance advantages you
can get out of dry sump system, but we never thought
they would consider it.
"We bid on doing the dry sump for
that engine but we did not get it, so we weren't really
involved in the production side too much. The actual
production dry sump system running the scavenge pump off
the crank, behind the pressure pump, I thought, was
pretty unique and it works pretty well. Certainly not an
all-out race set-up, but darn good for a production
Late LS7 oil pan. Image: GM
Actually, "dry" sump is a misnomer
because it's not truly dry, at least in the sense of
some of the complicated dry-sump systems on C5-Rs or a
NASCAR Sprint Cup car. The LS7 system is more of a
"semi-dry" sump in that there's oil inside the crankcase
and the oil pan. What's different is the "sump"
part–that is, the engine's entire oil supply–is not
stored in the lower part of the oil pan beneath the
crankcase, but rather in a remote-mounted tank. The oil
pan contains a limited amount of oil, because, when the
engine is running, it's constantly drained or
"scavenged" by a "scavenge pump".
"GM had never developed one
before," John Rydzewski began his discussion of the
dry sump. "We benchmarked systems on racing engines
and from other manufacturers which have (production)
dry sumps like Porsche and Ferrari. We saw how
complicated they are. You can do a very complex,
multi-scavenge with each (crankcase) bay
scavenged individually by a pump having five stages,
like on a race engine. That's the extreme and not what
we wanted for this car. We wanted something to give us
the performance we needed. We wanted it more affordable.
We wanted to make it as compact as possible."
LS7, two-stage oil pump
components. Image: GM Powertrain.
The LS7 development team settled on a
two-stage design. Gen 3/4 engines already had
crankshaft-driven, gerotor oil pumps, so it made sense
to add a second gerotor scavenge pump. Both are inside a
two-cavity housing located at the normal oil pump
position on the front of the block.
Oil is sucked out of the bottom of
the pan, into the scavenge pump, through a passage in
the bottom of the pan, then through hoses and into the
dry sump tank located in the right rear corner of the
engine compartment. Oil enters the bottom of the tank
and flows through a tube to the top of the tank. Flow
then reverses through a system of baffles and
perforations, down the inside perimeter of the tank.
That spiraling, downward flow separates the air and
crankcase gases out of the oil.
The Camaro LS7 oil tank.
Image: GM Powertrain.
The lower part of the tank is the
engine's oil reservoir. The air and gases rise to the
top, are ingested by the Positive Crankcase Ventilation
(PCV) system and consumed by the engine. At the
bottom of this tank is conditioned oil–"conditioned"
meaning the vast majority of air and gases are gone and
it's a little bit cooler because it's been in the tank
for a while. On top of that, as the engine is subjected
to accelerating, braking and cornering forces, the
pick-up tube is always submerged. It doesn't suck air
and that's the key to the reliable, consistent oil
supply an LS7 needs.
An LS7 oil heat exchanger.
Like most road racing engines, the
Z/28's dry-sump system includes an engine oil cooler. It
is an oil-to-coolant heat exchanger originally developed
for the C6 Corvette ZR1 and is bolted to the oil pan on
the driver side of the engine.
One of GM Powertrain's strong points
is its ability to engineer really great cylinder heads
and, the LS7 is clearly demonstrative of that ability. A
forged crank, Ti rods, lightweight pistons and dry sump
oiling are neat stuff in any production car, much less
one of the Vette's price range, but, from a performance
standpoint; the most significant pieces of hardware on
an LS7 are its cylinder heads.
Although C6 debuted in 2005 with the
LS2, Gen 4 Small-Block V8 under the hood, the LS2 head
was a actually a Gen 3 hand-me-down, having been used on
the 2001-04 LS6. The LS7's head was the first Gen 4 head
to go to production and if there had been a mission
statement for its development, it might have been:
"maximum performance with minimum complexity".
In late-Summer, 2003, the Society of
Automotive Engineers magazine Automotive Engineering
International published an article about a head with
three valves-per-cylinder being part of a 500-hp,
Corvette engine. Math art in the AE article and
photos which appeared on the Internet later showed
complex pushrod valve gear. This article sparked
speculative chatter on Internet forum sites along with
articles in other magazines suggesting that a 24-valve
engine would be in the "next" Z06.
The most important part on
the engine is this cylinder head. Ti intake, raised
ports, rolled-over 3° and fully CNC'ed. It's the key to
the LS7's amazing performance.
Image: Mark Kelly/GM
While the the "3-valve" had been
under development by GM's Advanced Powertrain Group and
might even have been a last-ditch attempt at getting
500-hp out of a 6.4, it was never a part of the LS7
program. The team at Powertrain working on the
seven-liter stuck with the two-valve configuration which
had worked so well with the LS1, -2 and -6 engines. In a
discussion of the three-valve head, Jordan Lee, who's
now Chief Engineer for Small-Block V8 Engines, told the
CAC, "Our philosophy is not to add technology for
technology's sake. If technology is really not a
performance benefit, we won't implement it." As
such, the three-valve head became part of the LS7
mystique and another curious footnote in Corvette engine
A prototype Gen 4 V8 with the
three-valve head circa Summer 2003. Image: Dave Emanuel.
Using computer analysis tools, port
models in "flow boxes" and single cylinder test engines,
the cylinder head team, under Design Responsible
Engineer, Dennis Gerdeman, developed and tested a
multitude of intake port, exhaust port and combustion
chamber shapes before ordering any prototype LS7 parts.
This process added two more big architectural changes to
the square ports and revised pushrod locations developed
for the six-four head. First, valve angle was decreased
from 15° to 12°. Secondly, intake port was raised. Its
floor was lifted 9-mm. (.354-in.) and its roof was
raised 5-mm (.197-in.), for an overall cylinder head
height increase of 7-mm (.284-in.). These changes
improved air flow. Also, at this point in the
development, combustion chamber displacement was set at
70-cc's. For this article, the CAC recorded a long
interview with Dennis Gerdeman. It began with a
discussion of the early LS7 head work.
"We were working on this (6.4L
LS6 successor) and they gave us a target (450-hp)
and we achieved it early in development," Gerdeman
told us. "It wasn't long after that when (GM
upper management) came back and said, 'We need to
raise the bar and increase our target to 500
horsepower.' It was really late in the development stage
and that sent us all scrambling. That's when we started
pulling out all the stops–the bigger bores, the titanium
rods and inlet valves–and really stretched the limits of
"It was (early) 2004 when
we were going through this accelerated development
crunch. A lot of it was hardware. When we were looking
strictly at air flow, we were doing a lot of work on the
air flow bench, nearly all of it with single cylinder
flow models. From an air flow analysis standpoint, we
were very limited back then. We weren't nearly as
developed in CFD (Computational Fluid Dynamics)
analysis tools as we are, today."
The head is cast of 356-T6 aluminum
by Nemak using the semi-permanent mold process and
cold-box cores. For machining, the head is shipped to
the same Linamar facility which does the block. An LS7
head is machined entirely by five-axis, Computer
Numerical Controlled (CNC) machining centers having
automated tool changing. The use of 5-axis CNC allows
all machining operations of critical head
features–ports, chambers, valve seats and the deck–or
"joint surface" as cylinder head engineers say–to be
accomplished with no set-up change between them and that
enhances the accuracy of the machine work. We asked
Dennis about the decision to use all CNC machining for
the LS7 head.
Top is the LS3 descendant of
the 6.4 head and bottom is the LS7 head. They were
photographed from slightly different angles so, due to
an illusion, the LS7 port size doesn't seem as large as
the 6.4's but it is. The key features of these two
images are the difference in valve angles along with: 1)
the contour of the short turn radius of each head and
how the LS7's more developed short turn improves air
flow and 2) the height of the LS7's port floor and how
the port entry is raised up above that of the six-four.
"The Engine Power Analysis Group
told us, 'You're gonna need such-and-such air flow to
have a chance at 500 hp.' We had a good feel for the
geometry we needed for the perfect transition from the
ports, across the valve seat and into the chamber. We
also needed to reduce cylinder-to-cylinder (air
flow) variation and you just cannot get there with a
conventional casting and machining process.
"With conventional castings–and we
have some excellent casting suppliers–their variation is
too high to ensure those perfect transitions. With
conventional plunge machining of the valve seat and
casting draft (note: "draft" is the slight taper,
perpendicular to parting lines, required with sand-cored
features of semi-permanent mold castings, such as ports.
This "core draft" is required in order to extract the
sand port cores from the steel tooling in which they are
created.), you can't get those perfect transitions.
That's when we decided to CNC. At first it was the
chambers and the valve seats but then, looking at the
ports, we said, 'There's no way to get the airflow we
need without CNC machining there, too.' The only way to
get that is to do an unconstrained, three-dimensional,
CNC'ed port shape.
"We have the seats and guides
installed. They CNC the ports, chambers and seats in the
same machine set-up. There's no stack-up from
fixture-to-fixture–little or no variation from the CNC
porting, to the seat machining and to the joint surface,
so our chamber volumes and our seat machining
transitions are as good as you can get. It all comes
down to the repeatability of CNC machining. Any
variation from that is very, very small."
Other subjects Dennis and I covered
were how Katech's C5-R engine program influenced the LS7
cylinder head development and valve unshrouding.
Finally, we got into Mike Chapman's work.
When a valve opens, there are parts
of the valve opening which are closer to the combustion
chamber or cylinder bore walls than the rest. The
closeness of these walls is called "shrouding" and it
restricts air flow though the valve opening. Obviously,
the more you move the valve opening away from the
chamber or bore walls–i.e.: "unshrouding" the valve–the
less restriction there is and the better your air flow
"We went to the C5-R guys at
Katech and looked at their valve geometry, sizes,
positions relative to the bore walls and we decided that
was a great place to start," Gerdeman continued.
"We took the six-four head and kinda melded it into
stuff that we gleaned from the C5-R. We still had to
start with the six-four head because there were certain
manufacturing limitations far as geometry and production
durability. The C5-R. started us down the path of
siamese valve seat inserts, which was a real unique
feature for us–something we'd never done before. The
siamesed seats were driven by the valve size and getting
maximum unshrouding from the bore wall. We were making a
lot of prototype flow boxes that we could measure on a
flow bench and playing with different configurations
but, until we went siamesed (and unshrouded the
valves); we just weren't getting the air flow we
A key development in the
early stages of the LS7 head program was going to siamesed valve seats. That unshrouded the intake valve
thereby improving airflow.
"We had transfer machining lines
at the time. On a transfer line, trying to change things
like valve angles and locations is impossible without
huge investment. We decided, with this volume, to go
with an outside machining company. After sourcing, it
turned out to be McLaren which ended up (Sept. 2003)
getting bought by Linamar.
"McLaren had worked with Chapman
Racing. They said, 'Hey, talk to Mike (Chapman)
and let him take a stab at this thing.' We had already
developed a siamesed layout and what we thought we
wanted for unshrouding and valve sizes. Chapman started
working through the intricacies around the valve seat,
the angles, the blends to the port and the port's
geometry around the valve guide. He did a lot of
tweaking of port shapes. At the time, we were pretty
happy with our intake flow–Chapman did a couple little
tweaks there–but he spent a lot of time on the exhaust
valve seat and port."
Next we got into a long discussion
about various design features of the LS7 which
contribute to its performance. The first subject Dennis
covered was the all-important short turn radius which,
for those who are learning cylinder head nomenclature,
is where the port floor curves down, then transitions to
the valve seat.
The short and long turn radii
along with those transitional areas of which Dennis Gerdeman spoke during our interview are easier to
understand when you have a saw-cut head to look at.
"From an inlet standpoint, it's
the height (of the port), the shape of the short
turn and the area schedule–how the (cross-sectional)
area changes as you go down the length of the
port–that's important. We spent a lot of time developing
the short turn and from a CAD standpoint, it was a lot
of complex geometry because, whatever we ended up with;
we had to have a CAD model.
"Another focus was the shape of
the seat insert after CNC machining and its transition
across the 45° valve seat and into the chamber. Making
those transitions as smooth as possible and as much like
a radius as it comes out of the port and into the
chamber is another key feature. You want those
geometries as close to a radius as possible, but you
still need a very defined flat for the valve seat,
itself. There are four angles plus a radius. It is very
subtle as the fourth angle blends into the radius. This
radius is different on the short turn side than it is on
the long turn side. The short turn, the long turn and
even the sides: they're all a little different–another
advantage of CNC machining. If it's a cast port or an
as-cast seat insert, you are driven to the same
geometry all the way around.
"The exhaust side is very
similar," Gerdeman continued. "Again, there's a
unique area schedule. We spent a lot of time on the
exhaust fine tuning that. Also, the exhaust has even
more of a pronounced difference between the short turn
and the long turn sides.
The exhaust port–the parts of
the chamber just below it have the same type of turn
radii and transition areas. You can see why LS7s exhaust
ports flow really well. Image: Author.
"Area past the guide is critical,
but we still had to keep as-cast material around the
valve guide for temperature control to avoid durability
issues. In some (racing) cylinder heads, almost
all the as-cast aluminum is gone–racers will feather the
aluminum material out almost to a knife-edge adjacent to
the guide. We've got to still meet our durability
targets, so we can't machine it all away. The valve
guides are installed in the head prior to the CNC
machining. We have an as-cast port shape which provides
roughly 1.5-millimeters of finish stock (left for
the CNC work) everywhere. When they do the CNC
machining, they have to come up and clear that valve
guide insert. The CNC program can only get so close, so
you're going to see as-cast material (at the end of
the guides) just because of that.
"It's really designing the entire
chamber as a complete system. It's the maximum
unshrouding on the sides where the valves come closest
to the bore wall. The key is developing blends and
transitions so the airflow across the valve seat stays
attached to the shape of the chamber and ports as much
as possible. In the case of the inlet, air flow comes
across a very open area towards the exhaust side and you
want it to stay attached to that wall. Any time you
start getting detachment of the air flow, whether it's
the ports or the chamber, you get turbulence which
drives your effective area down and you start losing air
flow. It's like you're making the port or the chamber
"The four angles on the intake
seat really help, even with high lift flow. The more
angles you can cut, the more of a perfect radius you end
up with. At low lift, a lot of flow on the inlet side is
going to come from the unshrouding of the valve and how
far it is from the bore. Then, at the higher lifts, it's
how well you can keep that air flow attached to the
walls and reduce turbulence.
"We worked the backside of the
intake valve and the geometry transitions across the
seat angles to valve stem. We, also, tried various valve
margin heights and settled on what we have there as best
for air flow."
Near the end of the LS7 cylinder head
development, Gerdeman and his team looked beyond just
air flow. They studied how the air and fuel mixed in the
chamber as it flowed across the valve seat and as it
continued to mix once the intake valve closed and the
compression stroke began. They, also, looked at the
homogeneity of the mix near the spark plug and, once the
ignition kernel developed, how the flame front
propagated across the combustion chamber.
This is a view from the port
entry, down the intake port towards the valve guide.
Note how the guide is streamlined but not knife-edged or
removed all together like is done with some racing
heads. Image: Author.
Same type of view down the
exhaust port. Image: Author.
Some of this research was done at
Chapman Racing with a "wet flow bench" which mixes
colored liquid with air flow inside a transparent bore
to simulate a mix of fuel and air flowing into the
cylinder. The see-through bore and the color allowed the
cylinder head engineers to observe the homogeneity of
the air-fuel mix as it came past the intake valve seat
and flowed across the chamber then into the bore as the
piston moved down in the cylinder. The LS7's cylinder
volume was huge and getting a homogenous a mix as
possible was a challenge but an absolute necessity if
the engine was going to meet fuel economy and exhaust
The engineers' observations at
Chapman racing encouraged them to experiment with a
aerodynamic device in the roof of the intake port
between the valve guide and the long turn radius.
Described by Dennis Gerdeman as a "wing," it looks more
like a ridge or a deflector. It is intended to impart a
specific directional swirl to the flow as it enters the
cylinder bore while the piston moves down on the intake
The motion imparted by this deflector
is complex. It's somewhat like swirl, towards the spark
plug, but it, also, generates downward spiraling motion
towards the centerline of the bore. In the end, this one
feature of the LS7 intake port did much to enhance the
homogeneity of the air-fuel mix in the engine's large
cylinder volume and contributed to the engine's high
The deflector which was added
to the intake port just above the valve after research
on Chapman Racing's web flow bench. What's to bet half
the head porters who've tried doing LS7 heads, grind
that away? Image Author.
Interestingly, while Chapman's wet
flow bench was cutting edge stuff in 2004, it's an
anachronism, today. By the late '00s, GM's analysis
capabilities had grown tenfold such that CFD, with an
enhancement called "rain drop analysis," could simulate
wet flow down ports, though valves and seats and into
cylinders and do it in a few hours of computer time
rather than weeks of work with flow boxes on a wet flow
Judy Jin, Design Release Engineer for
the LS7 cylinder head, tells us that two different valve
seats are used. The intake seat is made of a specific
material, PMF 28, which is compatible with the titanium
intake valve. The seat couldn't be too hard because,
once you wear through the titanium valve's hard-faced
coating and into the softer, but very abrasive titanium
below, both parts fail in short order. You have to
protect that coating, but still have a seat that's hard
enough to avoid valve seat recession. Since they had
never done titanium intakes before, the cylinder head
team consulted with Federal-Mogul, seat insert supplier
for other aluminum Gen 3/4 heads, and leveraged F-M's
experience with titanium valves for racing. Actually,
the first material F-M recommended and GM tested, PMF
28, turned out to be the one which worked.
copper-infiltrated LS7 exhaust valve
seat prior to installation in the
head. Image: Author.
The exhaust valve seat, also supplied
by F-M, is Brico 3220 material, used in a variety of GM
aluminum heads. The Small-Block does not have coolant
flowing completely around the valve seat inserts.
Because of the siamesed valve seats, there's no cooling
at all in the "valve bridge" between the ports. When
things get extra hot, you want rapid transfer of heat
away from the valves and seats and into the water
jacket. For that reason, the exhausts use
"copper-infiltrated" seat inserts. Federal-Mogul, takes
a powdered metal blank and puts a copper cap over it.
They run it though an oven, the copper melts and wicks
into the microscopic voids in the powdered metal. The
copper-infiltrated seats improve heat transfer out of
the valves, through the seats and into the water jacket
Ms. Jin added that, because the valve
centerlines are so close, the valve seat installation at
Linamar is a multi-step process, most of which is done
in the five-axis CNC set-up which also machines all
other critical features of the head. First, a separate
CNC cuts a small "scallop" into each intake seat insert.
Next, during the head's main CNC session, the seat
pockets are cut such that they overlap slightly,
creating the siamesed appearance. The round exhaust
seats are installed into the head's exhaust seat pockets
and, finally, each intake seat insert is installed with
its scallop fitting over the side of the adjacent,
exhaust seat insert. This process eliminates any
“bi-metal” machining of the pockets which would occur if
the exhaust insert was installed into the head, first.
This is the preferred process because the seat pocket
tooling produces the highest quality results if it cuts
Judy Jin, a Small-Block
cylinder head engineer, led the discussion about LS7
valve seats and valve seat and face angles. The
finishing of the valve faces and seats–four angles on
the seats and two or three on the faces–is more
sophisticated than most production engines and more
typical of a racing head. Image: Author.
This image details the space
near the intake valve seat. The LS7 intake seat and
transition areas are a very sophisticated system
intended for one goal: maximum air flow.
The surfaces in the vicinity
of the exhaust valve seat are designed with optimal
exhaust gas flow in mind. Image: Author.
After the seats are installed, they
are machined to the proper angles. On the all-important
intake, starting at the combustion chamber roof, the
seat angles are: 39°, 45°, 60° and 71.83° followed by a
radius. The exhaust seats are cut with 38.17°, 45° and
76° angles, then a radius. In both cases, the valve face
seats on the 45° portion. Each seat and radius are
machined by one milling tool in a single plunge movement
of the 5-axis CNC's table.
The internal structure and the
cooling jackets of the LS7 head are much the same as
that of other Gen 3/4 heads going back to the LS1.
"Nothing special in the cooling jackets compared to
other Gen 3/4s. You try to get the coolant as
close as you can everywhere else on the back side of the
chamber, "Dennis Gerdeman told us, "but you still
have to have very large fillets to handle the high
combustion pressures. It's structural integrity vs.
cooling, so you have to strike a balance between the
two. Nothing different though than the other Gen heads.
They all have that same balance."
Even seemingly minor features can be
of utmost importance, such as the small horizontal pad
in each combustion chamber next to the spark plug.
"Those are 'locators,'" Dennis told us. "When the
casting is first set-up for the initial machining
operation, they need locators. Each chamber has one
because you want them all to be common (have the
same displacement), but we use the pads in two end
chambers and a horizontal pad on the intake side of the
deck face as the initial locating points for the
machining operations. We don't machine them away
because, if we ever have an issue identified later on
and believe it's a casting issue, we want to be able to
go back to the cast locators and take CMM (coordinate
measuring machine) measurements."
Linamar also assembled the heads then
shipped them to the PBC in Wixom. When you see one of
these heads before it goes on an engine, you'll marvel
at its appearance and feel. Its huge, glittering, CNC'ed
ports, gleaming titanium intake and stainless steel
exhaust valves and the shimmering, silvery combustion
chamber walls are sweet eye candy for we engine guys. "The
appearance of the CNC work is a balance between cycle
time and surface finish," Dennis Gerdeman commented.
"Ideally, you'd want to make it smoother but when it
really came down to it, the gains were marginal at best.
The cycle time already is so long. When you consider you
have to do eight ports and four chambers and all the
seat machining, it's a lot of time in the machine. Each
head takes about two hours."
Left to right: the Author,
Performance Build Center Engine Assembler, Mike Priest
and GM Powertrain Communications Manager, Tom Read. We
all agree. Each of us should have one of these heads on
display in our living rooms because they are so pretty.
Image: Mark Kelly/GM Powertrain.
Even the exterior surfaces of the
heads have a "premium" look and feel because of the
semi-permanent mold process used to cast them. Like the
crankshaft, the LS7 head is one of those parts that's
just too damn pretty to be run on an engine. All and
all, it's a high-tech piece both in performance and
appearance. An interesting bottom line on the LS7 head
comes when one compares it's airflow numbers with those
of the head on the Camaro SS's LS3. In a straight-across
comparison, the LS7 head flows about 20% more air, a
We asked Dennis Gerdeman, if he could
revisit the LS7 head design, today, what he'd do
differently. "From an analysis standpoint, our tools
have improved significantly over what we had back when
we developed this cylinder head," Gerdeman replied. "I
would probably play with valve sizes, again, and
locations within the chamber just to see if there's a
little more we could squeak out of this from an airflow
perspective. I don't think it would change
significantly, but we may have ended up with a little
larger exhaust–maybe a slightly smaller intake. It may
even have led to a slightly different intake port shape
with a different area schedule.
"Those are probably the two things
I'd like to revisit: the intake port and small tweaks to
the valve sizes or centers, because with the tools we
have today, you can accomplish that in hours instead of
weeks. Before you had to make a CAD model, send it to a
job shop and have them cut you a flow box then, flow it
on the bench and try again. Now we can do it with
analysis in a fraction of the time."
The LS7 head gasket is
standard faire for today's high-performance engines, a
3-layer, multilevel-steel (MLS) design.
Dennis and I ended our LS7 cylinder
head discussion talking about how the engine's mystique
comes from the power it makes without boost and its
drivability. "When you think what you can pull out of
a Small-Block naturally-aspirated–making that
500-hp–it's pretty amazing," was his final
Cam and Valve Gear
LS7's valve train was yet another
field on which GM Powertrain moved the technology ball
forward for another first down. Not only does the LS7
have a hydraulic lifter valve train which runs to 7100
RPM, 500-RPM higher than that of the C5 Z06 engine and
beyond the capability of even the solid lifter engines
of the bygone Musclecar Era, but it has a huge, 2.20-in
intake valve–the largest ever in a production GM
V8, besting the 2.19 intake used in Camaro
high-performance 396 and 427 Big-Blocks of
late-'60s. Valve lifts are an astonishing
.593-in. and .589-in. for intake and exhaust, a
significant leap past the '02-'04 LS6 camshaft,
previously GM's most aggressive. Duration at
.050-in. lift jumped 6° to 210° on the intakes
and a whopping 20° to 230° on the exhausts.
While lift and duration are often cited in
comparisons of cams, a more telling measurement
is lift area which, when you graph the valve
lift, is the area below the curve. With the LS7
cam, compared to LS6, lift area rose 12% on the
intakes and 15% on the exhaust, both significant
Like all roller cams, the LS7
unit is machined from a steel billet. The lifters come
in fours in plastic lifter guides. Image: Author.
(All lift figures are valve
(All lift figures are valve
"The design philosophy on that cam
is similar to the LS6, the ramp designs are very
aggressive," Jim Hicks, who lead the LS7's
valvetrain development. "We were limited in what we
could do with camshaft because you've got a cam bearing
diameter and the nose can only go so high. We had to
drop the base circle down to a smaller radius so the
nose radius could be larger. In addition to that, we
went to the higher rocker ratio and that gets us to the
(valve) lift we needed. Then, we tried to make
everything as light and as stiff as possible.
The higher rev limit, a
gargantuan intake valve, more aggressive valve
train velocities and a big increase in lift area
required some trick valvetrain features
previously reserved for racing applications. The
first task was to reduce valvetrain mass.
Inspired by Katech's C5-R 427s using a titanium
intake valve, Hicks and the LS7 valvetrain
engineers decided on a Ti intake and a
hollow-stem exhaust valve as two ways to get the
mass down. Despite a valve head which is 22%
larger, the ti intake weighs 19-grams less–a 21%
reduction–than the smaller diameter and shorter
stemmed, LS2 intake valve. The ti intake valve,
supplied by long-time titanium valve
manufacturer, Del West Engineering, was the
World's first application of the super-light
metal in a production automotive valvetrain.
Back in the day, people
thought any high-RPM application needed a dual-row,
timing chain, but in recent years, GM has developed some
pretty stout single row, true rolling chains. Evidence
of that is the LS7's timing set. Still not convinced?
The Katech chain set, as used in the C5-R 427s, is,
also, single row.
This is what a PBC assembler
sees during LS7 assembly–a view only an engine wonk can
love, if you ask us. You can't miss the humongous Del
West titanium intake valve. A small chamber, siamesed
seats and minimum valve shrouding means the valves
almost touch each other. The curves of the chamber walls
and roof along with the CNC machining is sweet eye
candy, too. Image: Author.
"We started with a hollow-stem,
steel valve, kinda like the LS6, with a very thin head,
"Hicks said. "We reached a point where the power
the engine was making was flexing the valve head enough
that we had problems with the valve heads cracking.
Combustion pressure causes the valve head to flex.
Imagine pushing on the top of a tin can, moving it
in-and-out. If the section (thickness of the valve
head) gets too thin relative to the amount of
pressure in the chamber, you'll get this flexing and,
eventually, a pie-shaped section breaks off. We found
this with test engines. At the time, we were, also,
doing some work with Katech. They were using a lot of
our parts in the World Challenge, the first year of the
Cadillac CTS-V program and they failed some of our
valves, as well.
"We had to make a change and going
to a thicker-head steel valve wasn't an option,"
Hicks continued, "because we wanted a 7000 RPM red
line. We looked at a couple of alternatives–some really
kind of radical. ultra-light steel valves. I tested a
few of those and they failed miserably. Then we said,
'Alright. We gotta do what ever it takes.' We went to
the titanium for mass and strength because, with the
titanium head you could go to a flat, almost no cup on
the combustion face–make a nice, thick section through
there–and not take a big mass penalty, so you end up
with a lighter valve which is also strong. (The LS7
intake) was the first production application for Del
West and the largest diameter titanium valve in any
Jim Hicks, who was the lead
engineer for the LS7 valvetrain explained that the cam's
base circle was made smaller so the effective lobe lift
would increase. That along with 1.8:1 rockers resulted
in the amazing (for a production cam) valve lift. Image:
The same protective, CrN coating
used on the connecting rods is on the intake valves but
getting that coating just right was a tough task for Jim
Hicks and the engineers working on the LS7 valvetrain.
One of the issues they had to address was a "Ti dust
wear" problem, similar in nature to what afflicted the
connecting rod development. When the CrN coating wasn't
right, it would fail and highly-abrasive Ti dust would
develop between the valve stem and guide causing rapid
guide wear. "Developing the stem coating which was
going to work well with our production-style, PM guides
was another challenge. Most racers use bronze guides or
some other type of aftermarket guide which is
cost-prohibitive. A moly-sprayed stem, which is
typically used a lot on titanium valves (for racing),
is very expensive. We wanted to come up with an
alternative, so we worked on a chrome-nitride, vapor
deposition coating. It took a little development, but it
worked out really well for us. It was more
cost-effective and just as good or better than the moly
spray. There's some tricks to that process and we worked
with Del West in developing them. The parts need to be
very, very clean. The right processing steps need to be
used. The coating thickness is very important and needs
to be maintained to a tight tolerance. I think Del West
is using it now for some of their aftermarket parts,
Racy stuff–titanium intake
and hollow stem exhaust valve. The stems are gun
drilled, filled with sodium, the SilChrome head is
welded in place, then the valve is machined. Image: GM
The intake valve faces are machined
at 45°, 30° and 10° and this is done before the CrN
coating is applied because the coating also enhances
face durability of titanium valves. Typical of Ti
valves, tool steel "lash caps" are used on the ends of
the valve stem. "We actually tried to get away
without a lash cap," Jim Hicks said, "and do a
welded on, steel 'wafer' which was another development
program. We were trying to friction weld it. You can do
it, but it's not consistent enough and you can have some
which come apart. That program was unsuccessful, so we
ended up just using a conventional lash cap like they
use on racing engines."
The LS7 uses unique valve springs.
They are the typical GM "beehive" design, but they are
0.160-in. taller than all the Gen 3/4 springs GM used
previously. The extra height is to accommodate the LS7's
greater valve lift. These springs have 16-lbs. more open
angles on both valves. On the both
there is no specific top cut, rather
the part of the finish machining
adjacent to the 45° face is done at
10° on the intake and 25° on the
exhaust. Image: Author.
The exhaust valves have 2143
stainless steel heads for heat resistance and hollow,
sodium-filled, SilChrome stems which are
induction-hardened to have a good wear surface for the
rocker arms. The benefit of a sodium-filled, hollow stem
is mass reduction–about 18%–and, because sodium is an
excellent heat transfer fluid, getting heat out of the
valve head and into the guide. Exhaust face angles are
45° and 25°. Both valves move in powdered metal guides.
Lash caps go over the tip of
the stem of a titanium valve and prevent direct contact
between the rocker arm and the stem. Without a lash cap,
the stem of the Ti valve and the rocker arm tip would
quickly wear. "Beehive" springs have been used on Gen
3/4/5 engines since the Camaro LS1 was introduced in
1998, however, the LS7 uses a specific beehive spring
with more height and higher open pressure. Image: GM
LS7 pushrods are longer and
have a ticker wall than do other Small-Block units. From
a performance standpoint, the weight of the pushrod is
not as important as it's stiffness. Image: Mark Kelly/GM
To get to the 7100-RPM red line such
that the Z06 could go 0 to 60 in first gear required
more than just "light-weighting" the valvetrain on the
valve side of the rocker. It had to be as stiff as
possible on the pushrod side. The pushrods are steel
but, compared to other Small-Block pushrods, are larger
in diameter, have more wall thickness, and to
accommodate the taller head, greater length. Obviously,
all that makes for a heavier pushrod, but, from a
performance perspective, there is a greater benefit in
keeping the pushrod side as stiff as possible, as
opposed to as light as possible.
A pair of LS7 rockers showing
the offsets of the intake part. Image: Author.
The LS7 rocker arms are made of
investment-cast steel, the same material as other Gen
3/4 rockers. The investment casting process is ideal for
production roller rockers because it's strong, allows
complex shapes with mass only where its needed and is
cost-effective. The intake rockers are a unique design
with the pushrod seat offset 3-mm to the left and the
valve stem pallet offset 6-mm to the right, allowing the
pushrod to be moved over to make room for the revised
intake port location and shape. Typically, Gen 3/4
Small-Block rocker arm ratios are 1.7:1, however, the
LS7 was the first to use a 1.8:1 rocker ratio. The
reason for that extra "tenth-of-a-ratio is the same
reason hot-rodders put 1.6 rockers on traditional
Small-Blocks: more valve lift!
Lastly, the LS7s valve lifters not
only play an important part in the valvetrain's 7100 RPM
capability but they are a stalwart design, as well.
Other than some occasional small changes in oil metering
rates and plunger travel, the part used in a 2013 LS7 is
virtually the same part used in 1987, when GM introduced
roller hydraulic lifter cams to its engines with the LB9
305 in the old 3rd Gen cars. The same basic part, in
service for 26 years speaks volumes about the soundness
of the design
The LS7 hydraulic lifter is
durable at 7000 RPM. Amazingly, it's a 26-year old
design. It was introduced on the LB9 of 1987 and other
than some changes in hydraulics and plunger travel, it's
still used today. The trick, Chevy Performance lifter is
the same except it uses a lightweight ceramic check ball
rather than a steel ball as do OE lifters. Put those in
an LS7 with an aftermarket cam and, given the right
valve spring pressure, the engine can rev even higher.
Image: Mark Kelly/GM Powertrain.
Induction and Computers
The LS7's intake manifold shares some
qualities of previous Gen 3/4 intakes. It's made of
black Nylon 6, no coolant flows in it and the throttle
body and injectors bolt to it. Other than that, it was a
new design. "We had to match to a different port in
the cylinder head," John Rydzewski told us. "We
tried to get as much flow as possible. The intake
runners are sized and tuned for the engine's performance
envelope. They're a little bit shorter (than those
of LS1, 2 and 6). It's a three-piece, molded and
vibration-welded assembly with a seal to prevent
crosstalk between runners. It uses a 90-mm throttle
body, the biggest we make at GM."
The LS7 intake is a bit
different than that used previously. Obvious is its
rectangular rather than round ports. Maybe not so
obvious is a bit less runner length to better suit the
LS7's torque curve. Image: Author.
The intake manifold, throttle body,
fuel injectors and fuel rail are assembled by a supplier
and shipped to the Performance Build Center in Wixom as
one piece. The LS7 uses a "4-bar" fuel system which
runs at 400-Kpa or 58-psi. The injectors flow
5-gram/second (39.6 lbs/hr.) at 58-psi. They're made by
Bosch have all stainless internals–the norm because of
ethanol-blended gasolines–and are a
The LS7 debuted in 2006 with the GM
E38 engine controller which uses a Freescale Power PC
chip as its main microprocessor. Interestingly, the
Power PC "Reduced Instruction Set Computer " (RISC) chip
was originally developed in 1991 by an alliance of
Apple, IBM and Motorola (now Freescale) for Macintosh
personal computers. Today, Freescale PPC chips are
common in all kinds of automotive engine control,
chassis control, body control and telematics
The LS7 throttle bore is
90-mm, biggest in GM. Even the LSA's throttle body has
only an 87-mm. bore. Image: Author.
There are four slightly different
versions of the LS7's E38. The first was used in '06 and
'07, the second in '08, the third in '09 and '10 and the
final variation for '11-'14. All these different
versions increased processor speed, enhanced memory maps
and eventually added a second micro processor.
Z/28s E38 engine controller. Image:
The Final Push
As the LS7 development closed on
deadlines forced by GM's intent to debut the engine in
the 2006 Z06, the engine's power output had plateaued
somewhat below the 500-hp goal set by that pesky senior
For a while it looked like 480 was
going to be the number," Corvette Chief, Tadge
Juechter recalled in a Spring 2012 interview with the
CAC, "but then, they pulled the rabbit out of the hat
at the end. This was on the eve of production! I'm
talking about the end of '04. We're already ordering
material to build our nonsaleable validation vehicles at
the plant so, we're holding up the presses at that
point, trying to decide–'Ok, guys, what is the
horsepower?' and remember, it was, also, the first
engine in the auto industry certified to (the
then-new) SAE standard. That was another level of
rigor that we had to go though. The very last part
released for production was the Z06 badge which said
'505-hp'. In fact, we were thinking we'd have to go to
production without any number on there because we didn't
know what it was going to be."
In this final six-months the
key advance which put the LS7 "over the top" was a late
modification to the LS7's cylinder case. As we said in
the first part of this article, early in the development
program, unlike its predecessor LS6, the LS7 block had
no main web windows for bay-to-bay breathing. The CAC's
discussions with former LS7 boss (and current Chief
Engineer for V6 engines), Dave Muscaro, revealed how his
team found about another 10-hp by developing block
windows which did not compromise strength. "We were
pushing 490-495hp for about the last 6 months of
development," Muscaro told us. "The one area we
knew still had promise was in our bottom-end breathing.
If we could improve bay-to-bay breathing, we could
reduce the work required by the bottom side of the
pistons to move air around. The Corvette is extremely
challenging in this area due to the engine's low
position in the car. The ground clearance requirements
disallow ample room in the oil pan to aid in lower end
breathing which puts additional challenges on finding
ways to reduce the (power loss in) lower end
"So (while other areas of the
LS7 development moved ahead) we continued to look for
ways to improve breathing by way of the engine block
itself. The LS6 utilized openings in the main bearing
webs to help its bottom end breathing but, up to this
point, we had not been able to identify similar LS7
engine block changes that could withstand the additional
loads put on it by the power levels being achieved.
After numerous design iterations run through structural
analysis computer modeling, we came up with engine block
design revisions (one was the change in hone
over-travel radii discussed earlier) that
incorporated bay-to-bay breathing portals–known as hone
met all structural durability requirements.
A computer rendering of the
window and hone over-travel machining which was a big
player in GM's final effort in the ruthless pursuit of
power which resulted in 505 horses: Drawing: John Rydzewski/GM Powertrain.
"That final look in this area",
Muscaro continued, "gave us a design which met
the structural requirements and one which we knew would
also improve our lower end breathing and therefore
increase the engine's power output. Blocks were ordered
to this design revision and we began testing them. In
those tests, as predicted, we saw an immediate
improvement in our bottom end breathing as demonstrated
by the engine's power level increase of 10-15 hp. We
proved the revision's durability and made the new block
part of our production package."
That last block change and a few
other little tweaks saw final development LS7s meet the
500-hp goal senior management set almost two years
before. The engine was revealed to media in January 2005
at the Detroit Auto Show. GM had decided the LS7 would
be certified using the Society of Automotive Engineers
(SAE) then-new Standard J2723 "witness test". The SAE
Standard to which the dyno test data is corrected had
not changed–it was still J1349. What's different is: for
a manufacturer to say an engine is "SAE-certified"
requires that manufacturer test the engine in an
ISO9000/9002-approved dynamometer testing facility and
that the testing be witnessed by persons approved by the
SAE. On 14 March, 2005, the J2723 testing was done and
the engine produced 505 SAE net horsepower at 6300-RPM
and 470 SAE net pound/feet torque at 4800-RPM. A little
over three weeks later on, 10 April, the LS7 was the
first engine to ever have its power output certified to
the SAE J2723 standard.
We let Dave Muscaro have the final
word on the LS7 development. "Working in GM like we
do, we work as a team. We don't 'win individually' nor
do we 'lose' individually. Rather, when we create a
successful production engine program, like the LS7, the
whole team has reason to celebrate. Was I glad to be a
part of it? You bet! I worked with many great engineers
and I sweat the details on each part of the engine with
each of them. I learned from them how to make each of
their parts great, and when we put them all together, we
had the LS7. From airflow and CNC'd ports to all the
lube challenges high g-forces bring, to offset rocker
arms and titanium valves/rods, to a very large throttle
body and a forged crank–we all sweat many little
details. So in the end, I consider myself very fortunate
to have worked with all these great engineers who helped
create the LS7 engine."
Power For Another Z
Fast forward to summer 2011. As to
where the GM marketing and engineering folks got the
idea to stick the LS7 in a Camaro and make a killer
track car? Chevrolet hasn't offered much about the
Z/28's origins and development, perhaps because, when
the car was introduced in New York, the final stages of
that, along with SAE and government certification
testing, were not complete.
We'll guess that, about the time
Camaro engineers were in the middle of developing the
1LE package for 2013 SSes, they, also, watched as Ford
upped the ante with the 444-hp, light-weight, Mustang
BOSS 302 Laguna Seca. There might have even been a few
internal emails which could have said something like:
"Oh s&%t. We didn't go far enough with 1LE!"
Monterey Historic Automobile Races in 2011
as the backdrop for its media preview for
the BOSS 302LS. Image: Ford NA
Part of the solution, of course, was
the Corvette Z06's LS7, which made Ford's supercharged
five-liter seem kind of puny. It had 505-hp, weighed
less than the supercharged LSA, was the same size as the
existing LS3 and, best of all, since the C6 Corvette
would cease production in February of 2013, leaving the
PBC with some unused capacity, a modest quantity of the
engines could be available. All that would be necessary
to get the LS7 into a Camaro was a few unique induction
and exhaust parts along with calibration, validation and
certification. The Camaro structure had already proven
capable of supporting 556-lbs/ft. torque, but the LS7
only made 470. Through the ZL1 and 1LE projects, a lot
of pretty stout driveline and suspension parts already
The BOSS's engine is this
444-hp, 302 cuin., DOHS, supercharged V8. News Flash:
this engine's specific output is 1.47, but the big dog
of supercharged pony car engines is Chevy's LSA, with a
specific output of 1.53.
Image: Ford NA Communications.
It didn't take a rocket scientist to
see a potential match made in heaven. We'll guess that
sometime in late-2011 or early-2012, at the Camaro
Development Team and at John Rydzewski's Passenger Car
Small-Block group over at Powertrain, a project got
underway to adapt the LS7 for use in a Camaro lighter
than a 1LE. The two big development changes for a Z/28
427 came with the air filter assembly and the exhaust
manifolds. Other changes were relocating the dry sump
tank from the right rear to the front of the engine and
changes to the LS7's accessory drive necessary to make a
non-A/C version of the engine available.
Because of the limited space
under a Camaro's hood, the LS7 air filter assembly and
air duct had to be a unique design. Obviously, the 90°
bend adds restriction compared to the C6 Vette design,
so the Z/28 uses a conical, oil-cotton air filter
element to gain back some of that lost airflow. Image:
Because of the limited space under
the hood of a Camaro, the original air filter assembly
developed for the Z06 wouldn't work so, the Z/28 LS7 got
a unique air box. Like that on all Camaros, it's on the
driver side, behind the radiator core support and
connects to the throttle body by an air duct with a 90°
elbow. The mass air flow sensor is between the elbow and
the filter mount. To restore some of the airflow lost
with the duct, there is an open element,
oiled-cotton-gauze air filter typical of aftermarket
Camaro air boxes.
The Camaro LS7 exhaust manifolds. Again, limited underhood space forced a somewhat more restrictive
design than used on a Corvette so, GM went with a
stainless steel, Tri-Y configuration which tucks in
close to the engine and exits near the rear of the
block, rather than the C6 Z06/ZR1 unit, which is a
shorty header with a center exit. Image: GM Powertrain.
The exhaust manifolds are different,
too, because of the same underhood packaging
constraints. Rather than the Z06's shorty header, the
Camaro engine uses a fabricated, stainless steel "Tri-Y"
manifold. The four primary pipes are grouped, according
to the engine's firing order, into two pipes and then
into a collector just above the outlet flange which is
located at the rear of the engine. While the Z/28's
exhaust manifolds and its exhaust system are somewhat
more restrictive than what was used on the Corvette Z06,
the performance hit is only about 1%–a minor issue.
Heck, you might gain that back simply by going to
ester-based, synthetic lubricants in the engine,
transmission and rear axle.
About a year later, word of this new
variation of the LS7 began to leak out, first, with the
2014 Camaro VIN Card surfacing and, then, after New
Year's, sparse chatter around Camaro Nation hinting of a
secret development project, known as "The HP". That veil
of secrecy was lifted at the New York Show with the
introduction of the Z/28
Every engine manufacturer does
reliability and durability testing. "Reliability" is the
quality of being consistent in performance, i.e.:, not
failing. "Durability" is the quality of being able to
withstand wear, i.e.: being reliable for a long period
of time in service.
John Rydzewski and Jim Hicks touched
on the reliability of individual parts such as titanium
rods and intake valves during the discussions we had
with them. Once the entire engine reaches a
near-production form, its durability testing begins.
Back in the old days–say the late-'80s–some of the
testing was on the dynamometer, but a lot of it was in
cars on test tracks. In recent years, with advances in
dynamometer technology and with the application of
computer controls, more of the testing is done in dyno
cells fitted with equipment which can alter the engine's
attitude to simulate various acceleration, corning and
braking loads. Even with all this advanced dyno testing
ability, GM still track tests engines in cars as a final
validation of the engine's performance, reliability and
During the cylinder head discussion,
Dennis Gerdeman, talked about durability testing.
Would premium ester-based
lubricants gain back the 5-hp loss? Image: Red Line
Synthetic Oil Corporation.
"We had a durability schedule that
we were running," Gerdeman said. "They call it
the 24-hour track schedule. It was kind of our benchmark
as we were going through the final validation of the
hardware, from the whole-engine perspective. They ran a
lot of these 24-hour track schedules, so we got quick
overnight results. It was a very strenuous test. They
did run the cars on the track, but most of (the
durability testing) was on engine dynos. We could
validate any corrections we were making to any of the
hardware components–not necessarily to the cylinder
head, but to valve train related pieces and all the
other mechanicals–pistons, cams and so forth."
Another standard GM Powertrain
torture test to which the LS7 was subjected is a
300-hour dyno test at wide-open throttle with the load
varied such that the engine goes back and forth between
peak torque (4800-RPM) and peak power (6300-RPM) in 125
RPM increments. The LS7 also was brutalized with a
"thermal shock test" which runs engine coolant ranging
between -40°F (burr) to about 250°F (ouch!) through the
engine while it's running.
LS7 at a Glance
Bore center distance:
Bore x Stroke: 104.775 x
101.6-mm/4.125 x 4-in.
Compression ratio: 11.0:1
Power: 505-hp@6300 rpm
rpm SAE net
Fuel delivery: sequential
port fuel injection
Fuel required: premium
Emissions controls: 3-way
catalytic converters, positive crankcase
Many people were interviewed for this
article and many others assisted in it's production.
Thank you to: At GM: Harlan Charles, Mark Damico, Monte
Doran, Dennis Gerdemen, Tom Halka, Don Henley, Jim
Hicks, Tom Hill, Judy Jin, Tadge Juechter, Jordan Lee,
Yoon Lee, Dr. Jamie Meyer, Dave Muscaro, Bill Nichols,
Rob Nichols, John Rydzewski, Mike Priest, Shane Smith,
and Sam Winegarten. At Katech: Jason Harding, Fritz
Kayl, and Kevin Pranger. At Mahle: Aaron Dick. At Del
West, Shannon Decker and Mark Sommer. At MPK Photo: Mark
Kelly. At Performance Publishing: Dave Emanuel. At:
Maritz: Meg Conroy.
Special thanks to Tom Read, Manager
of GM Powertrain Communications.