|
Yet Another, New Cam
While the new catalyst technology is the revolutionary part of LS6 for MY02, changes in camshaft profile and valve gear are, also, a major part of the improvement. The ’02 LS6 cam is an evolution of the ’01 unit. While the ’01 has only .525-in. lift, GM designed the LS6 intake port to work well at .550 lift, which means the port had additional potential given more camshaft. Back when the ’01 LS6 was introduced, I viewed that as a clue of what was to come for MY02 and I was right.
The 405 horse camshaft has a more aggressive profile. In fact, it’s got the highest valve lift of any camshaft ever installed in a production small-block V8, Generation I, II or III. "We spent a lot of time developing a new cam," Juriga told us.
The 405 horse camshaft has a more aggressive profile. In fact, it’s got the highest valve lift of any camshaft ever installed in a production small-block V8, Generation I, II or III.
|
 |
|
During his media briefing on the "Ruthless Pursuit of Power," John Juriga explains the differences in ’02 and ’01 LS6 camshafts. When you have an engine with a specific output that exceeds that of the late, great LT5 and you do it with two-valves per cylinder and pushrod valve gear; you have every right to grin big. Image: Author.
Click Images for Larger View |
|
"It required the most engineering because it’s a fine balance to try and gain more airflow without disrupting emissions, loosing low-end torque or creating durability problems. We upped the lift from 13.3 to 14 millimeters on the inlet and went to 13.9 on the exhaust."
Going from .525-in. lift to .551-in lift on the intakes and from .525 to .547 on the exhausts while the engine’s rpm range and the camshaft duration remained virtually the same means something had to be done to the rest of the valve train to keep it in control at high rpm.
 |
|
Externally, the two sets of valves don’t look different, but these cutaways, made before the valve goes through the final machining steps, tell the story. There is a significant mass reduction in hollow stem valves. The one at center right is the exhaust valve and its cavity is filled with the Sodium-Potassium compound. Image: Author
Click Images for Larger View
|
|
"With the higher lift, we needed to reduce the mass of the valvetrain or start getting into a float condition," John continued. "We went to hollow stem intake and exhaust valves, very similar to what we used in the ’96 LT4. We pushed the edge–that’s what the Corvette is all about: pushing everything to the edge–with a state-of-the-art, 0.8mm (valve stem) wall thickness–very thin stuff. The exhaust stems are sodium-potassium filled."
The weight of each valve was reduced 23 grams. The ’01 intake weighed 99 grams and the ’02 weighs 76. The exhaust in MY01 weighed 86 grams but in MY02 weighs 63 grams. The exhaust stems are filled with a compound of 78% potassium and 22% sodium. "NaK" is unstable and may spontaneously combust when exposed to air with 50% or higher humidity. Do not cut open 02 Z06 exhaust valve stems.
|
|
As a result of the more aggressive cam profile, the valve springs were, also, changed. "Even with the lighter valves," Juriga said, "we still needed better control because we open and close them very fast. The closed seat loads are the same–400 Newtons (90lbs) on the seat–but the open loads increase from 1150N (259lbs) to 1310N (294lbs) for both springs."
A bigger cam, lighter valves, stiffer springs–so goes the ruthless pursuit of power.
An increase in air flow significant enough to provide 20 more horsepower also demanded a small change in the engine’s fuel and spark curves. This was done with slight alterations in the PCM calibration. There was no change in injectors or fuel pressure.
|
 |
| Juriga explains that valve springs
with 14% higher open pressure keep the engine out of valve float at high rpm. Image: Author.
|
|
|
