Abstract: Combustion induced motion of a piston in an internal combustion engine is augmented by the application of an intermittent or variable magnetic field reacting between the engine block and moving piston in a manner such that the piston is magnetically impelled along its path of movement. A permanent magnet is mounted on the piston with its axis of magnetic polarity aligned with the path of travel of the piston. An electromagnet mounted in the engine block is cyclically supplied with electric current to generate a magnetic field reacting with the magnet on the piston to cyclically magnetically attract or repel the piston in synchronism with the motion of the piston induced by fuel ignition. In the case of a reciprocatory piston, switching means are employed to reverse the polarity of the magnetic field in synchronism with the reversal of piston movement. Application of the magnetic field by the electromagnetic may be varied to occur over a selectively varied portion only of each piston stroke.