Abstract: An improved internal combustion piston engine that utilizes, in combination at least one poppet valve 52 of known type and a sleeve valve 5 to affect the functions of intake and exhaust gas flow. The resulting gross increase in valve area and volumetric efficiency enables the engine to produce high specific power without large valve opening durations or valve overlap and the resultant undesirable increase in low speed pollution and torque reduction. One embodiment of this invention will use the at least one poppet valve 52 as an intake valve, and the sleeve valve 5 as an exhaust valve. Another embodiment of this invention will use the at least one poppet valve 52 as an exhaust valve, with the sleeve valve 5 performing the intake valve function. Additionally, the sleeve valve may be either constantly or intermittently or incrementally moved to open or close a port through described methods.