An internal combustion engine that is comprised of a combustion chamber formed by a cylinder bore closed at one end by a cylinder head and by a piston reciprocating in the cylinder bore. At least one intake passage serves the combustion chamber through an intake port valved by an intake valve. A throttle valve is provided in the intake passage upstream of the intake port and is movable between an opened, full throttle position and a closed, idle position for controlling the flow through the intake passage into the combustion chamber. At least one exhaust passage serves the combustion chamber through an exhaust port. An exhaust valve controls the flow through the exhaust port. Valve actuating means are provided for operating the intake valve and the exhaust valve between their open and closed positions. The portion of the intake passage between the throttle valve and the intake port (intake passage volume) and the maximum volume of the combustion chamber when the piston is at its bottom dead center position (exhaust gas volume) are set to a predetermined ratio. The described constructions permit a very compact construction that permits the intake passage volume to be kept small to achieve the desired ratio.