Abstract: A four-cycle internal combustion engine with external ignition, which is equipped with an intake or suction manifold and with a separate forced air supply to the exhaust channels; to that end an air supply channel is cast-in adjacent one of the exhaust channels provided in a cast cylinder head, whereby the air supply channel is in communication with a slot extending along one suction pipe side in the longitudinal direction of the engine block; the slot is covered off on its open side by a flange of the intake or suction manifold and is operatively connected with the individual exhaust channels by way of cross bores provided in the cylinder head.