The use is described of the coherent anti-Stokes Raman spectroscopy (CARS) technique in a single-cylinderresearch engine to measure end-gas temperature in the regime that leads to the onset of knock. The investigations, under nominally the same running conditions, covered a large cyclic dispersion of knock, with knock occurring in about 80% of the cycles. In-cylinder pressures were measured with a transducer, and an ion gap signified flame arrival towards the end of the flame travel and just before autoignition. In general, the temperature increased by over 100 K, both with and without knock, as a result of exothermic preflame reactions. This measured elevation was supported by computations with a simple five-step model of autoignition, calibrated against measured autoignition times in a rapid compression machine. The temperatures measured just prior to knock increased with the severity of the knock. The observed severe cyclic dispersion of knock, under the conditions of the study, is attributed primarily to the cyclic dispersion of flame speeds. An increase in flame speed is associated with an increase in temperature and greater propensity to knock.