Additional Changes in the Intake and Exhaust Tracts
A unique item of Gen IIIs is the composite ("plastic") intake manifold. They offer low mass, low cost, and cheap manufacturing, but have expensive tooling costs as compared with aluminum or iron manifolds. Cost is why the performance aftermarket has, to date, not offered intake manifolds for the Gen III. GM knew when the LS1 went to production more performance would come from a revised intake manifold. The biggest change in the LS6 intake was an increase in plenum volume. This was accomplished by dropping the plenum floor down as low as allowed by the engine block valley cover. Additionally, sharp edges at the junction of the intake runners and the plenum were smoothed. Some dead air pockets (areas of no flow) were eliminated. The result was the new manifold being worth 10 horsepower, just by itself.
The other changes for the LS6 are the higher-capacity mass air flow (MAF) sensor from the 366-cubic-inch Gen III truck engine. It's worth 2-3 hp and its integral intake air temperature (IAT) sensor simplifies the engine controls and reduces cost. The LS6 also uses a different air filter assembly capable of slightly better flow.
The exhaust manifolds on the LS6 and 2001 LS1s are new cast-iron items. Previously, the LS1 used a double-wall, fabricated, stainless-steel manifold. Most '97-00 LS1s had cats downstream in the exhaust under the floor. Double-walls, available only with a fabricated manifold, were required to retain exhaust heat in the interest of quicker light-off of the catalytic converters. The addition of pup cats immediately below the exhaust manifolds on '00 California cars and all '01s eliminated the need for the stainless manifolds.
Closing Out The LS6 Story
The last major change made during the development was in the positive crankcase ventilation (PCV) system. In the fall of 1998, LS6 in-vehicle testing was underway at road race facilities in the north-central U.S. Once Z06 prototypes neared production, engineers noticed excessive oil consumption at high-rpm and high, lateral acceleration.
Further testing proved oil was being trapped in the valve covers, then sucked into the engine through the PCV system. The solution was new PCV hardware. Taking a page out of the LT5 book, LS6 uses a valley-mounted oil separator assembly rather than the rocker-cover units of the LS1. This significantly reduces oil aeration and oil consumption and simplifies the system.
The engine controls calibration for the LS6 differ mainly in larger capacity injectors and in fuel and spark schedules. The LS6 injectors flow 28.5 lbs-hr whereas the LS1 units flowed 25 lbs-hr The LS6's fuel cut-off is at 6,600 rpm. Of course, the first question enthusiasts are going to ask is, "What happens if I change the rev limit so I can run harder on the dragstrip?" We asked Juriga what keeps the LS6 from revving to 6,800 or so and he told us it was essentially the fuel cut-off. But he went on to point out that the total combination of components would be stressed if the engine was run any faster than that. Parts like rod bolts, pistons and bearings would be pushed to their maximum limits at those levels.
In 2003, Chevrolet will celebrate the 50th anniversary of the Corvette. It's a marketing guy's dream and a likely time for GM to introduce the next version of the Gen III. This writer's guess back in 1997 was the future "high-performance" iteration of the LS1 would come in a few years and be a "375hp class" engine. I was about a year off on when, but I was close on the power. My next fearless forecast? GM might call an even higher performance Gen III the LS7. I think it will be about the same displacement but will have a supercharger and about 425 hp.
Let's see if I'm right.