Abstract: A system for controlling the timing of poppet-type intake and/or exhaust valves in internal combustion engines of the four-cycle spark or compression ignition and two-cycle compression ignition type that may be normally aspirated, supercharged or turbocharged, wherein the timing is adjusted automatically or manually in relation to the speed of the engine to obtain optimum efficiency at any given speed. Dual camshafts are utilized, one for opening the valves, and one for closing the valves. An adjustable timing mechanism between the crankshaft and the camshafts simultaneously adjusts the opening and closing cycles of the valves.