Abstract: An exhaust system control apparatus for the exhaust of an internal combustion engine which is particularly useful on two-cycle engines. The exhaust system includes a subsidiary chamber connected to the normal engine exhaust passage with a valve for opening and closing communication between the chamber and exhaust passage to change the pressure wave at the engine cylinder exhaust port to provide optimum performance at high and low speeds. The chamber valve is operated rapidly by a pneumatic actuator supplied with compressed air from one or more of the sources disclosed, namely, a belt driven or electric air compressor and piston and cylinder devices extending between or forming the suspension components of a two wheeled vehicle. A pneumatic valve is operated by engine speed sensing means to supply or release the pressurized air to the actuator at a predetermined engine speed.

Abstract: Exhaust system control apparatus for internal combustion engine having an exhaust line and a branch line thereon, and an opening and closing valve on said branch line adapted to open when the engine operates at low speed and to close when the engine operates at high speed. The ratio between the cross-sectional areas of the branch line and the exhaust line is about 0.6 to 0.8.