Abstract: An ignition timing control system for an automobile internal combustion engine comprises knocking detecting circuitry, ignition timing control circuitry and inhibiting circuitry. The inhibiting circuitry is operable to interrupt the supply of an output signal from the detecting circuitry to the control circuitry only when the engine, which has been operated under a particular operating condition wherein the engine speed is lower than a predetermined speed value while the actual load imposed on the engine is larger than a predetermined load value, is operated under any one of operating conditions other than such particular operating conditions.

Abstract: A rotary piston internal combustion engine of the Wankel type for reducing unburned detrimental components such as NOx, HC, CO, etc. in exhaust gas without decrease of engine performance which comprises a first combustion chamber communicating by means of a passage means with a second combustion chamber formed between a trochoidal inner peripheral surface of a housing and a side surface of a rotary piston, said first combustion chamber being formed radially outside of said trochoidal inner peripheral surface, the volume of said first combustion chamber being 35 to 65% of the sum of both said combustion chambers at the top dead center (T.D.C.) of the engine, a fuel injection nozzle and an ignition plug provided in said first combustion chamber, said passage means opening onto said trochoidal inner peripheral surface in the range of 15.degree. before the junction of the two arcuate portions of said trochoidal inner surface to 30.degree.