Throughout turbo Ecotec dyno testing, GM Racing chilled the air-water intercooler with fresh tap water. At high levels of boost, pressurized air would enter the cooler at 200 degrees, leave at 105-110 degrees, with some creep due to packaging compromises and negligible pressure-drop. At the track, a dry ice heat-sink would reduce intake air exiting the cooler to 60-70 degrees.
At 450 hp and 8 psi boost, the GM team began blowing head gaskets. One theory was that core-shifting in the block was causing the gasket to fail (because some Honda motors have this problem). "I didn't buy it," says Bothwell. "But we tried converting the Ecotec block to a solid deck. This, unfortunately, just wasted time and destroyed some blocks, probably due to thermal-expansion issues."
The GM team decided the head was flexing. Returning to a stock-deck Ecotec block, they switched to high-strength H11 head studs. This restricted the head gasket leakage and failure exclusively to outboard sections of the fire ring at either end of the head on cylinders one and four. The GM team solved this problem by reinforcing the two problem areas with twin studs that threaded through bores machined into the upper structure of the head and jammed against the outboard fire-ring areas of the head next to cylinders one and four.
The engine now happily made 500 hp-and ran smack into the outer limits of stock coil-on-plug performance. Integral microprocessors will not allow the stock coils to energize and fire in the presence of excessive voltage. Short-term solution: GMR converted to a cam-driven distributor ignition with industrial-strength super coil.
Unfortunately, as power climbed toward 600, the entire block-head interface began leaking from the extreme combustion pressures. The GM team pressed stainless O-rings into machined grooves in the head, machined receiver grooves in the block and installed a soft copper head gasket. Problem solved.
At 600 hp, the extreme power and high engine speeds began distorting and flexing the aftermarket super-duty 4350 wrist pins. Left unattended, this would eventually tear out the pin towers below the wrist pins. In this same power range, the Ecotec's ring packs began failing. GM Racing opened the wrist-pin bores in the pistons by .003-inch and installed thicker H11 wrist pins with thicker walls. The team simultaneously migrated from the 1.0- x 1.0- x 3.0-inch aftermarket rings to Total Seal 1.5- x 1.5- x 4.0-inch ring packs.
The Ecotec was now finally reliable to 650 hp at 19 psi of boost-a relatively low level of boost, indicating outstanding volumetric efficiency. The GM team verified acceptable stress on all parts and lowered oil pressure to 85 psi after concluding that higher pump settings simply robbed horsepower and excessively aerated the oil.
The Push for 800 Horsepower
Consider this: 800 hp is a lot. On a 122 cubic-inch motor with 750 hp-three-quarters of a thousand-you're basically dealing with 6.14 hp per cubic inch. Pressures and stresses of all kinds-thermal and mechanical loading across the board-escalate to extreme levels. A Chevrolet 5.7-liter LS1 V8 with this much specific power (horsepower per cubic inch) would be making 2,137 hp.
GM Racing encountered a whole new world of problems between 650 and 800 hp on the Ecotec. Ring packs that worked fine at 650 hp failed to seal with acceptable blow-by as power approached 700. Pistons scuffed on cylinders, rod bearings began to go away. The ability to fire plugs through a 6 hp-per-cube mixture density required a radically powerful spark. Anti-detonation countermeasures of the highest order became crucial. GM Racing milled down the Ecotec plug bosses to accommodate a range of plug heat ranges.