Recently, motocross racetrack configurations have been changing from speed-oriented layouts to rider's talented performance-oriented layouts. This has created a demand for engines that can provide both power at high speeds and torque at low speeds as well as having quick response at all speeds. The most efficient way to achieve all round power range in the 2-stroke-racing engine was to increase the area of exhaust port and to vary the exhaust chamber volume at the same rate as the increased engine revolution. The authors developed an automatic exhaust control valve device called “KIPS”. In this paper we will describe how KIPS was developed, its output characteristics, and operation. Figure I shows a 1992 model KX250 motocross racing bike equipped with the newest KIPS device (3-Way KIPS).