How do Variable Valve Timing (VVT) systems work and what benefits do they provide?

VVT systems adjust the timing of intake and/or exhaust valve opening relative to crankshaft position, typically using oil-actuated cam phasers. Advancing intake timing improves low-end torque by allowing more air at low RPM, while retarding improves high-RPM power and enables internal EGR for emissions. Benefits include broader power band, improved fuel efficiency (2-5%), reduced emissions, and better engine response. Advanced systems like BMW VANOS and Honda VTEC also vary valve lift and duration.