Abstract: A valved conversion element for connection to a source of compressed fluid such as air or vapor and to a cylinder in an internal combustion engine. A sensor is provided which communicates with the pressure conditions in the cylinder served so that repetitive power impulses drive the piston in the cylinder as in normal operation of the internal combustion engine. The disclosure contemplates one valved element per cylinder in the engine and that the conversion be achieved by the manifolding of gas, vapor or fluid power to all cylinders through the conversion elements. Each of the conversion units is connected to the cylinders by means replacing the spark plugs of existing engines. Cyclic rate and power are adjustable by valve means controlling the quality and quantity of input fluid, such as air.