Knock control algorithms were developed for a spark-ignition engine. Spark timing was controlled using cylinder block vibration signal. The vibration signal of a 1.5 L four cylinder spark-ignition engine was measured using an accelerometer which was attached to the cylinder block. The maximum amplitude of the bandpass-filtered accelerometer signals was used as the knock intensity.Three different spark-ignition engine knock control algorithms were tested experimentally. Two algorithms were conventional algorithms in which knock threshold values were predetermined for each engine condition. Spark timing was retarded and advanced depending on the knock intensity in one algorithm and the knock occurrence interval in the other algorithm.The third algorithm was a new algorithm in which knock threshold values were automatically corrected by monitoring knock condition. Knock condition was determined by the nondimensional variance of the 10 cycles' cylinder block vibration data which were sampled continuousely for each cylinder. It was confirmed that the value of nondimensional variance could be used as a tool of knock threshold value determination.