Measures to improve specific fuel consumption of a spark-ignition engine have been taken by improving indicated thermal efficiency and reducing engine friction loss. In this work higher compression ratios have been used as a means of improving thermal efficiency and so improve specific fuel consumption. Higher compression ratios result in the phenomenon of knocking under full load and is studied in the article. The studies described evaluated the mechanism of knocking, and its relationship with combustion pattern, using a knocking-prediction mathematical model. The purpose of the study involved a need to control the knocking caused by a higher compression ratio, by means of modifying the pressure rise during combustion. (TRRL)