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. 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. 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. Each valve pair is controlled by one rocker arm, which is operated by the camshaft. 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. 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. 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. The 2ZZ-GE engine, the first and only engine to feature VVTL-i Variants of the system, including VVTL-i, Dual VVT-i, VVT-iE, VVT-iW and Valvematic, have followed. Adjustments in the overlap time between the exhaust valve closing and intake valve opening result in improved engine efficiency. Engine oil pressure is applied to an actuator to adjust the camshaft position. VVT-i varies the timing of the intake valves by adjusting the relationship between the camshaft drive (belt or chain) and intake camshaft. The VVT system is a 2-stage hydraulically controlled cam phasing system. The VVT-i system replaces the previous Toyota VVT system first introduced in 1991 with the five-valve per cylinder 4A-GE "Silver Top" engine found in the AE101 Corolla Levin and Sprinter Trueno. It was first introduced in 1995 with the 2JZ-GE engine found in the JZS155 Toyota Crown and Crown Majesta. VVT-i, or Variable Valve Timing with intelligence, is an automobile variable valve timing technology developed by Toyota. Cutaway view of Variable Valve Timing with intelligence on a ZR engine in Techniquest Glyndŵr
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