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Ruthless Pursuit of Power: The Mystique of the C6 Corvette LS7 Engine - Page 13 of 26


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Ruthless Pursuit of Power: Lucky Seven Edition: The Mystique of the 7-Liter, 7000-RPM, LS7 - Page 13 of 26

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by Hib Halverson
© May 2013— Updated:  November 2014
No use without permission, All Rights Reserved

Cam and Valve Gear

Like all roller cams, the LS7 unit is machined from a steel billet. The lifters come in fours in plastic lifter guides.

Image:  Author

Like all roller cams, the LS7 unit is machined from a steel billet. The lifters come in fours in plastic lifter guides.

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 Big-Block V8s of 1965-1972. 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 increases.

Camshaft Profile, Intake Comparison
(All lift figures are valve lift)

year
RPO
int.
lift
int. dur.
at .004
int. dur.
at .050
int. open
at .004
in. close
at .004
in. open
at .050
in. close
at .050
int.
CL
int.
area
int. area
increase
MY01 LS6 13.34 mm
.525 in
270° 204°
BTDC
81°
ABDC
18
ATDC
42
ABDC
118°
ATDC
1862.9
mm/deg.

-4%

MY02 LS6 14.01 mm
.551 in
267° 204°
BTDC
80°
ABDC
19°
ATDC
43
ABDC
120°
ATDC
1936.9
mm/deg.

0

MY05 LS2 13.34 mm
.525 in
270° 204°
BTDC
81°
ABDC
18°
ATDC
42
ABDC
118°
ATDC
1862.9
mm/deg.

-4%

MY06 LS7 15.06 mm
.593 in
276° 210°
BTDC
88°
ABDC
18°
ATDC
48°
ABDC
122°
ATDC
2166.4 mm/deg.

12%

Camshaft Profile, Exhaust Comparison
(All lift figures are valve lift)


year RPO
exh.
lift
exh. dur.
at. .004
exh. dur.
.050
ex. open
.004
ex. close
.004
ex. open
.050
ex. close
.050
exh.
CL
exh.
area
ex. area
change
MY01 LS6 13.33 mm
.525 in
275° 211° 65°
BBDC
30°
ATDC
37
BBDC
6
BTDC
114°
BTDC
1914.6
mm/deg.
-8%
MY02 LS6 13.91 mm
.547 in
282° 218° 69°
BBDC
33°
ATDC
42
BBDC
4
BTDC
115°
BTDC
2046.6
mm/deg.
0
MY05 LS2 13.33 mm
.525 in
275° 211° 65°
BBDC
30°
ATDC
37
BBDC
6
BTDC
114°
BTDC
1914.6
mm/deg.
-8%
MY06 LS7 14.95 mm
.589 in
296° 230° 81°
BBDC
35°
ATDC
53
BBDC
3
BTDC
119°
BTDC
2359.4 mm/deg. 15%

"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, told us. "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.

Image:  Author

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.

"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.

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

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.
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