Piston type air compressors are used to supply air under pressure for many purposes. Electric motors and internal combustion (I.C.) engines may drive the compressors. The air compressors have housings and cylinders formed with chambers for accommodating reciprocating pistons. The housings and cylinders are individually designed for use with heads and inlet and outlet structures for controlling the flow of air. Fins on the cylinders and heads are provided to dissipate heat to the surrounding air.