A system that provides adjustable actuation timing of one or more valve(s) (16) in a piston engine includes a position sensor (12) and a variable valve actuation assembly (10). The valve(s) (16) can be intake and/or exhaust valves in an internal combustion engine of an automobile. The position sensor (12) takes position readings of the valve(s) (16) as the valve(s) (16) actuate in the piston engine. The variable valve actuation assembly (10) controls actuation timing of the valve(s) (16). Actuation timing of the valve(s) (16) is adjustable based, in part or more, upon one or more position reading(s) of the position sensor (12). The variable valve actuation assembly (10) can be a lost motion assembly (10).