Abstract: A system for controlling the opening and closing, as well as the lift, of the intake and exhaust valves of an internal combustion engine as a function of the speed of the engine. In one form of the invention, the system includes a variable length tappet assembly which, in cooperation with a push rod and rocker assembly, functions to open and close the valves of the engine in direct relation to engine speed. The variable length tappet assembly is operably coupled with the oil pump of the engine, the output pressure of which varies as a function of engine speed with the result that the overall length of the tappet assembly also varies as a function of engine speed.