Abstract: A mixture-compressing spark-ignited four-stroke internal combustion engine having a combustion chamber bounded by the piston and the cylinder head, and inlet and exhaust valves, the valve openings of which are offset in plan view in the longitudinal direction of the engine with respect to a transverse plane of the cylinder and the valve stems of which form an acute angle when projected onto the transverse plane of the cylinder, and a squish area opposite a spark plug and parts of the inlet valve opening being masked and supplied with a mixture by a swirl inlet passage, the swirl inlet passage supplying a mixture to the inlet valve opening tangentially, a spark plug being disposed close to the center of the cylinder on the side facing the inlet valve opening, a squish area being provided opposite the spark plug amounting to between 5% and 15% of the cylinder cross-sectional area, and the inlet valve opening being masked on its flow downstream area toward the outer periphery of the cylinder by a downward projec