<P> VVTL - i (Variable Valve Timing and Lift intelligent system) (also sometimes denoted as VVT - iL or Variable Valve Timing and Intelligence with Lift) is an enhanced version of VVT - i that can alter valve lift (and duration) as well as valve timing . In the case of the 16 valve 2ZZ - GE, the engine head resembles a typical DOHC design, featuring separate cams for intake and exhaust and featuring two intake and two exhaust valves (four total) per cylinder . Unlike a conventional design, each camshaft has two lobes per cylinder, one optimized for lower rpm operation and one optimized for high rpm operation, with higher lift and longer duration . Each valve pair is controlled by one rocker arm, which is operated by the camshaft . Each rocker arm has a slipper follower mounted to the rocker arm with a spring, allowing the slipper - follower to freely move up and down with the high lobe without affecting the rocker arm . When the engine is operating below 6000 - 7000 rpm (dependent on year, car, and ECU installed), the lower lobe is operating the rocker arm and thus the valves, and the slipper - follower is freewheeling next to the rocker arm . When the engine is operating above the lift engagement point, the ECU activates an oil pressure switch which pushes a sliding pin under the slipper - follower on each rocker arm . The rocker arm is now locked into the slipper - follower's movements and thus follows the movement of the high rpm cam lobe and will operate with the high rpm cam profile until the pin is disengaged by the ECU . The lift system is similar in principle to Honda VTEC operation . </P> <P> The system was first used in 1999 Toyota Celica with 2ZZ - GE . Toyota has now ceased production of its VVTL - i engines for most markets, because the engine does not meet Euro IV specifications for emissions . As a result, this engine has been discontinued on some Toyota models, including that of the Corolla T - Sport (Europe), Corolla Sportivo (Australia), Celica, Corolla XRS, Toyota Matrix XRS, and the Pontiac Vibe GT, all of which had the 2ZZ - GE engine fitted . The Lotus Elise continues to offer the 2ZZ - GE and the 1ZZ - FE engine, while the Exige offers the engine with a supercharger . </P> <P> The Dual VVT - i system adjusts timing on both intake and exhaust camshafts . It was first introduced in 1998 on the RS200 Altezza's 3S - GE engine . </P> <P> Dual VVT - i is also found in Toyota's new generation V6 engine, the 3.5 - litre 2GR - FE first appearing on the 2005 Avalon . This engine can now be found on numerous Toyota and Lexus models . By adjusting the valve timing, engine start and stop occurs almost unnoticeably at minimum compression . Fast heating of the catalytic converter to its light - off temperature is possible, thereby reducing hydrocarbon emissions considerably . </P>

What is vvti and how does it work