ventillift

Ventillift, commonly referred to as valve lift in English, is the maximum linear displacement of a valve stem from its closed position to the fully open position in a valve-controlled mechanism, most often in internal combustion engines. It determines the effective opening of the intake or exhaust port and, together with valve duration and timing, influences the engine’s air–fuel flow and overall breathing characteristics.

Valve lift is produced by the engine’s valve train, typically driven by a camshaft. In simple terms, valve lift equals the cam lobe lift multiplied by the valve train ratio. With a direct-drive cam and a 1:1 ratio, valve lift equals cam lift. In configurations using a rocker arm with a mechanical ratio, valve lift can be greater or lesser than the cam lift (for example, 1.5:1).

Common values vary by engine design but typically range from about 5 to 12 millimeters for many automotive engines, with intake valves often slightly larger than exhaust valves. High-performance engines may use larger lifts, while engines designed for efficiency may employ smaller lifts. The choice of lift is interconnected with valve duration, port geometry, compression, and the desired power and torque characteristics.

Measurement and testing are usually performed with a dial indicator during valve-train setup or inferred from the cam profile and rocker ratio. Valve lift is part of the broader topic of valve timing, which also includes the timing of opening and closing events and the overlap between intake and exhaust phases.

Some modern engines employ variable valve lift systems to adjust lift during operation, enabling different breathing profiles at different RPM ranges.