Some superchargers list estimated gains on specific setups or kits. These dyno tested horsepower and torque results are an excellent baseline, but superchargers actually add horsepower as a percentage gain. On an engine with a compression ratio of around 9:1 running pump gas, if a supercharger gives your engine 14.7 psi of boost (1 additional atmosphere) the supercharger will basically double its output potential. Adjustments must then be made to this number for thermal and mechanical energy transfer. If an efficient supercharger is generating 7.5 psi (approx. 1/2 an atmosphere), you will see about 35-40% gain in horsepower and torque as compared to your non-supercharged maximum horsepower rpm. If detonation forces you to use an ignition/timing retard system, you will see less of a gain. Backing off several degrees of timing will greatly reduce an engine's power output. At higher boost levels, the heat generated by compressing air will diminishing the power return as the boost is increased. This may be reduced with the utilization of an intercooler system or upgrading from pump gas to racing fuel(increased octane rating). Adding an intercooler system allows you to run higher boost levels while maintaining reliability, 100% increases can generally be achieved at around 17 psi on an engine with 9:1 compression running pump gas. The gains in horsepower and torque delivered by each supercharger kit varies by application and can usually be altered or modified to best suit your performance needs and driving style.