In the small displacement, high-speed, high-performance spark ignition engines being developed by Honda, the difficulties in reducing exhaust emissions without seriously impairing inherent engine characteristics are different from those encountered with the large displacement engines generally used in American cars.This paper reports on some of research in the following areas: 1. Development of a control device to minimize exhaust emissions during the frequent accelerations and decelerations in normal driving conditions. 2. Application of the air injection reactor system in small displacement engines. 3. The effect of “squish action” in a hemispherical combustion chamber on exhaust emissions.Through research and development, many of the difficulties were overcome and satisfactory results have been obtained in exhaust emission control under certain limited operating conditions. The fundamental data and knowledge gained through this research will serve as useful reference in future studies on exhaust emission control.