Exhaust valve system for two-cycle engines

An exhaust valve system for internal combustion engine. The engine includes a cylinder having an exhaust port with an axial extent along the axis of the cylinder structure. An exhaust port valve is mounted adjacent to the exhaust port and is adjustable between a full-flow position, in which the exhaust port valve exposes the exhaust port throughout its axial extent, and a restricting position, in which the exhaust port valve restricts the axial extent of the exhaust port. A valve control module is connected to the exhaust port valve and functions to adjust the exhaust port valve between the full-flow and restricting positions in response to the cylinder bore gas pressure. At low speeds and low output conditions, the valve is in its restricting position. As the cylinder develops higher pressures at higher speeds and under higher output conditions, the valve control module moves the valve to its full-flow position.