Abstract: A two-stroke internal combustion engine has an inlet port in the cylinder wall covered and exposed by the piston during reciprocation thereof in the cylinder and to which fresh air is supplied under pressure by a supercharger. An exhaust valve is mounted centrally in the cylinder head for controlled operation independently of the position of the piston. Fresh air forced into the cylinder by the supercharger when the inlet port is exposed by the piston during the exhaust stroke enables any residual unburned gases to burn completely and expels the gasses from the cylinder completely enabling operation of the engine at high compression with relatively low pollution.