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Single-cylinder engine tests, with computerized data aquisition, of several nitroparaffin and methanol fuel blends were conducted to identify engine operating conditions or fuel compositions which reduced combustion knock with no penalty to engine power. The effect of variation in equivalence ratio, nitromethane percentage in selected co-solvents, ignition timing and compression ratio was investigated at fixed engine speed and steady-state temperatures. Electronic filters were used to isolate the portion of the cylinder pressure signal containing combustion knock and a Fast Fourier Transform computer subroutine was used to characterize combustion severity in the frequency domain. The results verified the empirical racing engine practice that for a nitromethane/methanol mixture operating fuel-rich from stoichiometric, power is increased and knock is decreased.