Abstract: My invention relates to means for and methods of increasing the compression ratio of the cylinders of an overhead valve engine. The means comprises a small plate of metal which is attached to the top face of the piston head. The plates are provided in various sizes so that one size may be selected to increase the compression ratio a predetermined amount.The method comprises removal of the engine head with the overhead valves carried thereby, and the rotation of the crankshaft to bring the pistons in any desired order to substantially top dead center, and to attach the compression-increasing plate to the top face of a piston while it is at top dead center.