Four-cycle engine

摘要

An engine induction system having a check valve upstream of the intake port for precluding reverse flow. A plenum device is communicated with the induction system downstream of the check valve for reducing inertial effects and improving charging efficiency. The plenum device may be the crankcase chamber of the engine. In that case crankcase ventilation may also be controlled and improved. Crankcase supercharging may also be generated. These features may be combined with variable valve timing to further improve engine performance.