Abstract: A variable displacement valve seat that consists of an annular ring which is affixed concentrically around a standard valve seat. The annular ring is affixed loosely to allow linear coaxial movement along the valve seat center-axis line. The movement is restricted to a small fraction of the valves actual displacement, approximately 12% or less, in the preferred embodiment. The annular ring is affixed to the valve seat insert installed in the cylinder head when used on the exhaust side. The annular ring is affixed to the head portion of the poppet valve itself when used on the intake side. The concept can provide an effective range of early closing times for the valves to control reversion. In addition, the actuation of the moveable seat is variable and automatic, and controlled by cycle exchange functions.