the engine has at least one cylinder each with at least one and preferably multiple air intake valves into the cylinder , and at least one exhaust port at a lower position above the bottom position of the piston . a blower is arranged to force air into each cylinder via each intake valve as the piston moves around the bottom position , the blower not supplying enough pressure to keep each intake valve open during upward motion of the piston , such that during upward motion of the piston , compression occurs within each cylinder , and such that during downward motion of the piston the blower forces air into each cylinder via each intake valve once each exhaust port is uncovered by the downward motion , and out of each cylinder via each exhaust port . the air intake valves are positively actuated by controlled air pressure differentials , for example by each intake valve having a valve disk to close against a valve seat , a valve shaft , and lower and upper guide disks . the lower and upper guide disks run in guide bores and act as actuating pneumatic pistons , the guide bores extending between an air supply chamber receiving air from the blower and a vacuum plenum . the guide disks thereby respond to a pressure differential between the vacuum plenum and the air supply chamber to actuate the valve .