Abstract: A fuel conserving engine improvement for a four-stroke cycle internal combustion engine of the type which includes at least a pair of complemental cylinders whose pistons reciprocate in unison, but on different strokes. The improvement includes a conduit providing communication between the combustion chambers of the cylinders through openings which are uncovered by the pistons at the bottom of their strokes whereby exhaust gases flow from the cylinder whose piston is completing its power stroke to the cylinder whose piston is about to begin its compression stroke. A blower operating through a check valve pulls gases from the crankcase and circulates such gases through the conduit for discharge into the crankcase when the conduit openings are uncovered after upward movement of the pistons.