The super-modified Ecotec was able to achieve a reliable 750 hp on 24 psi of boost at 9000 rpm with 10:1 compression and an unspecified fuel with extremely high octane and excellent heat of vaporization characteristics. But as Bothwell's team pushed power beyond the 750-plus range, GM Racing began to encounter such extreme cylinder pressures and thermal expansion that the thin-wall stock cylinder sleeves and support structure began to warp and go out of round, split. Cylinder-piston scuffing became a problem.
As of this writing, the team has developed a promising new "Super-Turbo" Ecotec, built in a process where a GMR machinist entirely removes the stock sleeves and aluminum cylinder support structure/core, pressing thick, custom-built bottom-flanged steel sleeves into receiver bores machined directly into the floor of the water jacket. GMR reinforces the new extra-thick full-floating sleeves with a pool of epoxy that effectively raises the floor of the water jacket to surround the base of the cylinders. As an anti-scuff countermeasure, GM Racing increased the cylinder bore clearance in the Super-Turbo engine by 0.001-inch, and shot-peened the piston skirts to help retain oil.
It's amazing that any components whatsoever designed for a stock 140-hp 2.2-liter Ecotec would survive on an extreme powerplant making more than six times the power. However, the stock Ecotec block and main/girdle structure did survive to 750 hp, as did the stock sleeves. The stock main bearings survived. The stock stamped roller finger-followers were effective to at least 9700 rpm, as were the hydraulic lifters. The oil delivery passages remained stock to 800 hp. The stock chains, guides, tensioners and water pump worked well all the way to heaven. The stock head survived with minor strengthening and massive breathing modifications. Many other components were good for two to four times stock power (see chart). GM Powertrain engineers designed a base engine with many stock components that were above and beyond what was needed for stock performance. "The crank support structure of the Ecotec is unbelievably strong," says Bothwell. "We detected no core shifting under the most extreme conditions."
The engine-fuel combination turned out to be extremely knock-resistant. The Ecotec combustion chamber is efficient, with excellent tumble and high flame speed, and the engine was able to run 10:1 compression without knock at boost pressures as high as 36 psi at 21 degrees spark advance. In a vehicle, the on-board computer is aware of which gear is in use and varies maximum boost accordingly to avoid detonation and traction problems.
From the excellent power-boost ratio of 750 hp at 24 psi, one can infer that careful turbo selection, camshaft selection and timing, good intercooling and carefully considered turbo system geometry result in a happy situation in which inlet manifold pressure exceeds backpressure in a happy phenomenon called crossover, where horsepower really skyrockets.
Turbo configuration and size would change three times during the tuning process. The highest-flow turbo is currently capable of delivering 40 psi boost at very high power levels. The largest Innovative wastegate is unable to divert enough exhaust to keep boost from creeping to a minimum of 15 psi when heavily loaded on the dyno, though this is not a problem on the track.