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

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°	9° BTDC	81° ABDC	18 ATDC	42 ABDC	118° ATDC	1862.9 mm/deg.	-4%
MY02 LS6	14.01 mm .551 in	267°	204°	7° BTDC	80° ABDC	19° ATDC	43 ABDC	120° ATDC	1936.9 mm/deg.	0
MY05 LS2	13.34 mm .525 in	270°	204°	9° BTDC	81° ABDC	18° ATDC	42 ABDC	118° ATDC	1862.9 mm/deg.	-4%
MY06 LS7	15.06 mm .593 in	276°	210°	8° 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.

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.

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.