More performance" is part of the mission statement of the Corvette folks at GM's Powertrain Division for 2002. That was made obvious when "Doctor" John Juriga, Assistant Chief Engineer for Gen III Passenger Car Engines announced that LS6 for MY02 will generate 405 horsepower and 400 lbs.-ft. torque, 20 more hp and 15 more lbs.-ft. over the '01.
Can You Feel The Difference?
Heck yeah-but only if you're driving a Z06 as it's supposed to be driven: real hard. The LS6's extra power is all up top and it makes the '02 Z06 the quickest production Corvette ever. Some intel we've developed about GM's in-house, '02 Z06 testing suggests an astonishing, 3.85-sec. 0-60 and quarter mile performance at 12.45/118.0 mph. That's using timing with no roll-out (rather than drag strip clocks), on a typical road surface and at the hands of a driver who understands how to launch.
The revised LS6, with 405 hp at 6000 rpm and 400 lbs.-ft. at 4800 rpm, makes the '02 Z06 a couple tenths quicker than last year's model and a full half-second quicker than the last of the ZR1s. At a ripe old age of 11, the ZR1's only remaining title is "Fastest Production Corvette" at 180 miles per hour.
LS6 Evolution: Bigger Cam Again
There are two big changes in LS6 for 2002. The first is evolutionary and the second is revolutionary.
The '02 LS6 cam is an evolution of the .525-inch-lift, 2001 part. It's more aggressive profile has the highest valve lift, about .550 inch, of any cam ever installed in a production small-block V8. We interviewed John Juriga for this article and he said about the '02 cam, "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."
We also spoke to the LS6 camshaft engineer, Jim Hicks, and he agreed. "Yeah, it was a fairly large challenge. We were taking the valve lift velocity and acceleration up to a new level. We have never run anything even approaching 14mm in the small-block's history-not in a production application, anyway.
"The most aggressive part of the profile is the intake event. We held the duration constant and increased the acceleration to get the added lift area. That was done to improve engine performance.
"The exhaust event we carried over the peak accelerations of the '01 LS6 cam and let the duration grow."
To preserve idle stability, the MY02 intake duration at .050-in lift was held to the '01 specification. Idle quality is a pleaseability issue with Corvette customers, but more importantly, it impacts exhaust emissions. For LS6 to meet the national low emission vehicle (LEV) standard, it's got to idle smoothly. With the intake duration frozen, the only way to increase air flow, and thus performance, was to add valve lift. The exhaust duration at .050 lift was lengthened and valve lift was added. Both increased exhaust port flow.
Another change made to preserve idle quality was to spread the lobe centerlines apart. "We spread them by retarding the intake lobe two degrees and advancing the exhaust one degree," Jim Hicks said. "Typically, when you delay the intake closing point, you give up a little torque at low speeds, but it doesn't hurt power. In fact, if anything, it might help power a little bit.
"The main reason why they were spread like that is: with the longer exhaust duration, we had to spread the lobes to maintain overlap at the '01 LS6 level so the idle quality wouldn't be degraded.
"There was no downside from a power perspective and the torque really wasn't hurt either. We made up for it in the additional lift area."
Another major difference between 385-horse and 405-horse cams is the base circle radius. The base circle for the '01 LS6 is smaller than that of the LS1 and the truck cams, and for MY02, it's smaller yet. Most Gen III cams have a 19.7-mm. base circle but the '01 LS6's is 19.3mm and the '02's is 19mm. Both reductions were to accommodate increases in valve lift.
We asked Jim Hicks why the base circle had to get smaller when lift increased. "All of our cams (prior to LS6) had the same base circle radius. We had a problem with that base circle if we wanted to go to higher lifts: the nose of the cam would approach the same diameter as the cam bearing journals or even above them.
"Obviously, that means you can't install the cam in the engine-little bit of a problem. Your only alternatives are to increase rocker arm ratio, which we weren't going to do, or reduce the base circle radius."