Abstract: Disclosed herein is apparatus including all of the components present in a conventional internal combustion engine such as body forming cylinder walls that define a primary combustion chamber, a piston reciprocable in the cylinder between compression and power strokes, intake means for introducing fuel charges into the primary combustion chamber, ignition means for igniting fuel charges and exhaust means for removing residual gases from the primary chamber after ignition of each fuel charge. Added to these conventional engine components is a housing that defines an auxiliary combustion chamber and an orifice that provides communication between the primary and auxiliary combustion chambers.