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In an effort to help explain knock performance in a variety of engines, a semi-empirical knock model has been developed. Making use of a “lumped-parameter” autoignition model and simple cylinder-pressure-driven thermodynamics, the model mimics the knock results obtained in an engine with a central-ignition chamber remarkably well. While additional testing against other engines is necessary to determine the generality of the model, it has already proven useful in explaining experimentally observed trends. The current work indicates that while heavy knock may occur at temperatures above 1000 K, independent of “cool-flame” chemistry, threshold knock is a 700-950 K phenomenon which can be influenced by “cool-flame” chemical activity.