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The first functional variable valve timing system, including variable lift, was developed at Fiat. Developed by Giovanni Torazza in the 1970s, the system used hydraulic pressure to vary the fulcrum of the cam followers. The hydraulic pressure changed according to engine speed and intake pressure. The typical opening variation was 37%. The next big step was taken by Honda in the late 1980s and 90s, where Honda began by experimenting with variable valve lift. Pleased with the results, engineers took the knowledge and applied it to the B16A engine, fitted to the 1989 EF9 Honda Civic. From there it has been used in a variety of applications, from sport to utility, by many different auto makers. In the year 1992, BMW introduced VANOS, their version of a variable valve timing system, on the BMW M50 engine used in the 3 Series. VANOS significantly enhances emission management, increases output and torque, and offers better idling quality and fuel economy. The latest version of VANOS is double-VANOS, used in the new M3. Double-VANOS adds an adjustment of the intake and outlet camshafts. One thing that separates the BMW variable timing from what Honda developed is that VANOS provides stepless adjustments to the valve timing throughout a rpm regime to provide optimum timing at all engine speeds within that regime. Honda's VTEC triggers a single step change at in the timing when the engine speed reaches a preset rpm (this rpm occurs near high rpm ranges). Variable valve timing was the sole domain of overhead cam engines until 2005, when General Motors began offering the LZE and LZ4, pushrod V6 engines with VVT. For the 2006 model year, General Motors will introduce the Vortec 6200, the first mass-produced pushrod engine with variable valve timing. VVT Implementations • BMW VANOS - Varies intake and exhaust timing by moving the fulcrum of the camshaft • Ford Variable Cam Timing - Varies valve timing by rotating the camshaft • GM DCVCP (Double Continuous Variable Cam Phasing) - Varies timing with hydraulic vane type phaser (see also Ecotec LE5). • Honda VTEC - Varies intake, duration, and lift by using two different sets of cam lobes • Honda i-VTEC - Adds cam phasing (timing) to traditional VTEC • Hyundai/Kia CVTT • Mazda S-VT - Varies timing by rotating the camshaft • Mitsubishi MIVEC - Varies valve lift • Nissan N-VCT - Varies the rotation of the cam(s) only, does not alter lift or duration of the valves. • Nissan VVL - Varies intake, duration, and lift by using two different sets of cam lobes • Porsche VarioCam - Varies intake timing by adjusting tension of a cam chain • Porsche VarioCam Plus - Varies intake timing by adjusting tension of a cam chain as well as valve lift by different cam profiles • Rover VVC - Varies timing with an eccentric disc • Suzuki VVT • Subaru AVCS - Varies timing (phase) with hydraulic pressure • Toyota VVT-i - Varies intake timing by advancing the cam chain • Toyota VVTL-i - Varies timing by advancing the cam chain and switching between two sets of cam lobes" http://en.wikipedia.org/wiki/Variable_valve_timing
