A reduction of engine knock intensity is demonstrated by incorporation of a stepped piston top to provide an abrupt increase in flame front area in an ASTM-CFR octane rating engine. The conclusions are based on several different types of knock measurements. Three different piston designs were tested.Decreases in the knock intensity, the magnitude of the pressure oscillations following knock, of up to 40% were realized. The statistical nature of knock is shown to be somewhat different from a normal distribution. The data have more scatter, particularly toward the high side of the mean value.