Variable valve timing (VVT) is a system which optimises an engine's valve timing at all engine speeds, improving power throughout the rev range.

Engines without variable valve timing have a fixed relationship between the opening and closing of the valves and the motion of the piston. This relationship can only be optimal for one engine speed, because of inertia effects in the flow of gas past the valves and into the combustion chamber.

Variable valve timing systems allow the valve timing to be altered so that it is closer to optimal at all engine speed and load conditions. This allows the engine to produce more power at most engine speeds.