valvelift

Valvelift is the distance a valve travels from a fully closed position to a fully open position in a valve-train or valve-actuated mechanism. The term is most commonly used in the context of internal combustion engines, but it also applies to industrial valves where stem movement controls flow.

In engines, valve lift is determined by the camshaft lobe profile, the geometry of the valve train (such as rocker arms or pushrods), and the valve’s actuating components. Lift is usually specified as the vertical displacement of the valve at maximum opening, measured in millimeters or inches. Alongside valve duration and timing, lift governs the effective cross-sectional area through which air and exhaust gases can flow, thereby influencing engine breathing, power, and efficiency.

The choice of lift involves trade-offs. Higher lift can improve high-RPM airflow and peak power but may require stiffer valve springs, stronger components, and more careful sealing to avoid leakage or valve crash at high speed. Lower lift tends to favor fuel economy and low-end torque but can limit peak power. Valve float and mechanical interference become concerns at high engine speeds if lift is not properly matched to other valvetrain parameters.

Variations and innovations exist to modify valvelift during operation. Some engines employ variable lift or continuous variable valve-timing systems that alter lift (and sometimes duration) to improve low- and high-end performance, drivability, and emissions.

In broader contexts, valve lift can also describe the vertical movement of a valve stem in industrial valves, where the travel distance affects the valve’s flow capacity and control characteristics.