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What type of fuel do I need with a supercharged automotive or truck engine?

A supercharger kit can usually be tailored to your application to run the type of fuel you prefer. Recommended fuel types vary by fuel-injectors vs. carburetor, engine compression ratios, and whether or not you chose to intercool your supercharger system.

As a rule of thumb for Intercooled EFI/TPI applications with low compression ratios (less than 9.5:1), often high boost levels (14-17 psi) can be safely run with full timing on pump gas, and will produce horsepower gains of 75-100% (depending on boost level and the motor specs). For low compression EFI/TPI applications without an intercooler, boost levels above 5 psi will require the use of ignition/timing retard if you wish to run pump gas, and will produce lower horsepower gains (35-45%) than capable with an intercooler system. To decrease the risk of detonation, High boost levels (above 12 psi) should generally be avoided even with racing fuel on a low compression motor. As a general rule lower compression motors are capable of handling higher boost, and higher compression motors should run less boost. Most preassembled supercharger kits for street applications are designed for use with pump gas at full timing and will not negatively affect daily drivability.

For carbureted motors, the rules are slightly different. Carbureted motors can generally handle more boost than a comparable EFI/TPI motor because carburetors deliver most of the fuel to the engine in a liquid state. As this raw fuel atomizes from liquid to gas, an endothermic chemical state change actually occurs. This reaction draws heat and cools the incoming air. For low compression carbureted engines (9:1 or less) and average boost levels in the 8-14 psi range, pump gasoline works very well. Higher compression ratios (10:1 or greater) require lower boost levels, a higher octane fuel, intercooling, or some combination of these. Extremely low compression ratios (7or 8:1 range) can usually handle 12-20 psi on pump gasoline.

What is detonation? How can it be avoided? ►

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