GM Racing designed the turbo system around an advanced Innovative Turbo turbocharger with plenty of parts available to upgrade and tweak performance as required, plus a huge wastegate and pulse-modulated electronic controller. The GM team fabricated a gigantic custom air-water intercooler that could be cooled continuously on the dyno with tap water or with a dry-ice heat-sink at the track.
GM Racing subcontractor Shaver Specialties dramatically upgraded the Ecotec head with significant porting and maximum size lightweight stainless-steel valves. Current SS flow-bench data shows the ported head capable of flowing 272 cfm intake air at 0.450 lift and 175-207 cfm exhaust.
With valve seals removed to prevent high-lift collisions with the retainers, Crower cams provide total intake lift and duration of .46482 inches and 221.4 degrees duration, total exhaust lift and duration of .46737 inches and 221.3 degrees. Shaver employed a proprietary GM Racing solution to forestall valve float problems at high-rpm and boost (with an eventual goal of 10,000 rpm redline, GM Racing decided to delete the Ecotec balance shafts).
By this time, the Turbo Ecotec powerplant had grown significantly in width. The GM Team decided to rotate it forward by 33 degrees. This would help deal with multi-G effects on oil drain-back and dramatically reduce the difficulty of packing it in a racecar.
GM Racing converted the turbo Ecotec to a multi-stage dry-sump oil system designed to reduce crankcase windage and thus increase power by scavenging oil and crankcase gases directly from the cylinder head and oil pan into a high-volume external tank. From the tank, a separate pump stage would provide superior low-temperate, high-pressure lubrication with reduced aeration directly to the short block, head and turbocharger.
The GM team built a narrow, low-volume, forward-biased V-shaped oil pan that funneled return oil to dual dry-sump scavenge pickups. They opened up windows in the girdle of the "Slant-Four" to prevent oil from puddling at a relocated low point and killing horsepower by interfering with the crank at high rpm.
Quest for Failure: Boost
The new turbo Ecotec immediately cranked out 350 hp at 7000 rpm on 2 psi boost, and rapidly closed in on 450 hp with zero failures. "Our tuning strategy," says Bothwell. "Was to start rich with a computer-generated air-fuel map and sneak up on rich-best torque."
The new turbo Ecotec was definitely responsive: GM Racing set idle at 1800 rpm, and if you punched it quick, the unloaded engine would blow completely through the 10K rev-limiter in less than a tenth of a second. The team expected an Ecotec-powered drag car to launch at 8000 rpm and run all the way through the gears in the quarter mile, so they cared mainly about the 5-10K rpm range. In this range, GM Racing wanted the turbocharger to achieve any specified level of "full boost" nearly 100-percent of the time.
As testing continued, GM Racing monitored EGT and exhaust gas oxygen on all four cylinders. Full-power target EGT was 1,230-degrees F, and would never exceed 1,350-degrees. The team continuously logged all sensor and actuator data throughout the power quest. The routine was, run the dyno manually at an array of "breakpoints" of speed, loading and boost, holding the engine steady at each point to tweak various parameters that define optimal rich/best torque-using EGT and wide-range O2 data, fuel-rail pressure, torque and power read-outs, a remote-control electronic boost controller and a laptop computer to recalibrate injection pulsewidth and spark advance.