VVT

Variable Valve Timing (VVT) refers to a family of engine technologies that adjust the timing of the opening and closing of the intake and/or exhaust valves in internal combustion engines. By changing when valves open relative to piston position, VVT aims to optimize airflow throughout the engine’s operating range, improving power, fuel efficiency, and emissions.

Most VVT systems achieve this by varying the camshaft timing with respect to the crankshaft. This is typically done with a cam phaser and an oil- or electronically actuated mechanism that can advance or retard valve timing during operation. Some implementations also modify valve duration or lift, either in addition to timing changes or as part of a broader variable valve technology. In practice, VVT systems continuously or progressively adjust timing as engine speed, load, and temperature change.

Automakers have developed several proprietary implementations. Examples include Toyota’s VVT-i, Ford’s CVVT, Nissan’s VVEL, and Honda’s i-VTEC (which combines timing control with variable lift). The objective across these systems is to provide better low- and mid-range torque, enhanced high-end power, and reduced exhaust emissions, while maintaining drivability.

Benefits of VVT include improved efficiency, smoother idle, wider usable torque bands, and better response at various speeds. Limitations involve added mechanical complexity, potential oil quality sensitivity, and diminishing returns on certain architectures. Overall, VVT has become common in modern engines as a practical means to balance performance and efficiency.