At this point, the team began to pump up the volume in a rigorous series of tests while a crew stood by with fire extinguishers. Testing at a given power level concluded when the engine could survive a series of 8-10 full-power dyno "Sprints" from peak torque through maximum power in 50 rpm steps, concluding with at least six seconds at full power, for a total of at least 20 very hard seconds. GM Racing successively verified that the Ecotec survived happily at 200, 225 and 250 hp over numerous dyno pulls.
However, as the Ecotec pushed through 283 hp at 4400 rpm, all four connecting rods simultaneously failed catastrophically and smashed through the side of the block. Laboratory analysis subsequently revealed a mid-beam compression fracture on all four stock powder-metal rods. All other components checked out fine. GM Racing installed a package of components you'd certainly install if you were taking the trouble to open an engine to upgrade the connecting rods: Super-duty forged Crower X-beam rods-plus 10:1 JE forged pistons with thicker top ring lands and Hastings moly ring packs. The GM Racing team installed larger fuel injectors, and continued to lean on the engine. Power advanced quickly to 350 hp, at which point the engine ran out of breathing room on the exhaust side. The ratio of Reactants (exhaust) to Products (inlet charge) is very high on a nitrous motor. GM Racing found the stock Ecotec exhaust manifold became sufficiently restrictive above 350-hp that injudiciously adding more nitrous could actually make less horsepower-due to dramatically decreased efficiencies in scavenging exhaust gases from the combustion chamber clearance volume. "We finally made 370-375 hp on nitrous," says Bothwell, "but the engine was really pissed off."
Building the Turbo Ecotec
At this point, GM Racing abandoned nitrous, built an efficient turbo Ecotec, and pushed on with the business of making power. The strategy was, make it efficient from Day One, then turn up the revs and boost. Bothwell's goal: 10,000 rpm and 800 hp.
"We knew the stock crank would need replacing by 500 hp," says Bothwell. "Since we were going to need the rev capability, breathing and rod-stroke ratio of a square bore-stroke engine, we had Crower build a de-stroked forged billet 2.0-liter crankshaft and used it immediately from 350-hp." New, larger 4143 7/16-inch main studs replaced the head bolts to hold the new crank firmly in place.
The GM Team designed a tube-type stainless header fabricated to optimize the collection of exhaust pulses in the correct order to minimize collisions. With plenty of boost, the GM team knew the stock scroll-type plastic intake manifold could flow sufficient air for 500 hp. Since the goal was way beyond 500 hp, they fabricated an aluminum, straight-port dry intake manifold with high-volume plenum for the turbo Ecotec. To regulate big air flow, GM Racing pilfered the throttle body from an LS1 V8.