Abstract: A two piece intake or exhaust valve for internal combustion engines comprising an inner and an outer valve which can be designed with orbicular heads. The inner valve including a stem of a smaller outside diameter than the outer valve. The outer valve including a hollow stem large enough to accept the inner valve, and also including a valve seat in the center of its bottom face to seat the inner valve. The head, or base, being equipped with one or more vents which communicate between the intake port and the combustion chamber and being releasably opened and sealed off by the inner valve. The vented valve unit incorporating an independent actuation means by way of pressure differentials created by the induction cycle, and/or directional inertia factors of the mechanically controlled valve element.