The project's magic is in the engine controller's instantaneous changeovers for the different tunes. For that, Martin developed three distinct engine calibration maps and relied on a FAST XFI controller to hold and administer them. (FAST also supplied its XIM ignition controller to drive a set of GM coil packs.) To switch fuels, Strayhorn simply selects a tune by turning a dash-mounted selector and, if necessary, manually changes the fuel tank source. A laptop is only required if fine-tuning of a particular fuel table is desired--but the calibrations are each tuned for street/strip performance.
The Chevy II even has separate fuel tanks for the gasoline and ethanol. Beneath the trunk floor is a modified original tank that features baffles to suit the requirements of the EFI's requisite high-pressure fuel system, while inside the trunk is a 5-gallon fuel cell for the alternate fuel--and it doesn't matter which tanks holds which type of fuel.
A pair of hand-operated valves in the trunk directs the fuel delivery from one tank or the other. A power-operated setup was considered, but Strayhorn felt the manual option was the safest way to go, especially at the dragstrip.
E85 Surprise
The basics of the engine's rotating assembly and cylinder heads comprise nothing exotic. It's an easily duplicated formula that includes: 4.130-inch x 4.000-inch stroke (428.6 ci), an all-forged rotating assembly, Profiler cylinder heads, a 9.5:1 compression ratio, and a Comp Cams custom blower grind with 0.651/0.646-inch lift, 239/248 degrees of duration at 0.050, and a 114-degree centerline.
The engine is built using GM Performance Parts' LSX cylinder block. Because it's cast in iron, it can be bored--unlike the aluminum production blocks--and it's designed to support big-boost combinations (see "LSXasaurus," HOT ROD, Nov. '08). In addition to the assembly work at Martin, Engine Systems in Tucker, Georgia, also contributed to the short-block buildup.
The engine combo, combined with the trio of fuel setups, was proven on Martin Motorsports' engine dynamometer--with surprising results. The relatively high octane rating of E85 enables more aggressive timing than premium pump gas, so nobody was surprised when the dyno pulls on the E85 tune produced greater results: about 805 hp and 670 lb-ft versus 750 hp and 640 lb-ft on 93-octane pump gas--although 750 streetable horses on pump gas are certainly nothing to apologize for.
The eyebrow raiser was the E85's trumping of the 108-octane C12 racing fuel's performance. It delivered approximately the same peak numbers as the premium pump gas but with a stouter power curve. It should be noted that the charge cooler was not activated during the dyno tests. Harold Martin suggests the natural cooling attributes of the alcohol-based E85 contributed to its significant performance boost over the higher-octane C12.
"That's one of the benefits of running alcohol at the dragstrip," he says. "The engine runs cooler, so you get a denser charge, even without an intercooler."
There is power to extract from the engine with more tuning time. Martin suggests there is perhaps 15 to 20 percent more power to be had from the gasoline tunes when their charges are blown through the functioning cooler--and more from the E85 tune, too.
By the way, boost pressure for this combination was about 8 to 10 psi for all three fuel types.
Strayhorn plans to put this triple-threat LSX to the test on the dragstrip as soon as the car's assembly is completed. He'll also hit the streets in his alternative fuel-powered Chevy II, undoubtedly blow-ing minds and turning heads when he does.
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