thumb|4B11 MIVEC engine
MIVEC (Mitsubishi Innovative Valve timing Electronic Control system) is the brand name of a variable valve timing (VVT) engine technology developed by Mitsubishi Motors. MIVEC, as with other similar systems, varies the timing of the intake and exhaust camshafts which increases the power and torque output over a broad engine speed range while also being able to help spool a turbocharger more quickly and accurately.
MIVEC was first introduced in 1992 in their 4G92 powerplant, a 1,597 cc naturally aspirated DOHC 16 valve straight-4. At the time, the first generation of the system was named Mitsubishi Innovative Valve timing and lift Electronic Control. the MIVEC-equipped engine could achieve at 7500 rpm. Similar improvements were seen when the technology was applied to the 1994 Mitsubishi FTO, whose top-spec GPX variant had a 6A12 1997 cc DOHC 24-valve V6 with peak power of at 7500 rpm. The GR model, whose otherwise identical powerplant was not MIVEC-equipped, produced at 7000 rpm by comparison.
Although initially designed to enhance performance, the system has subsequently been developed to improve economy and emissions, and has been introduced across Mitsubishi's range of vehicles, from the Mitsubishi i kei car to the high-performance Lancer Evolution sedan to the Mirage/Space Star global economy car.
Newest developments have led to MIVEC system being evolved into a continuous variable valve timing and also being the first VVT system to be used into a passenger car diesel engine.
Operation
Variable valve control systems optimize more power and torque by varying valve opening times and/or duration. Some of these valve control systems optimize performance at low and mid-range engine speeds, while others focus on enhancing only high-rpm power. The MIVEC system provides both of these benefits by controlling valve timing and lift. The basic operation of the MIVEC system is altering the cam profiles and thus tailoring engine performance in response to driver input.
In essence, MIVEC serves the same function as "swapping cams", something that car racers might do when modifying older-design engines to produce more power. However, such swaps come with a compromise - generally yielding either greater low-end torque or more high-end horsepower, but not both. MIVEC achieves both goals. With MIVEC, the "cam swap" occurs automatically at a fixed engine speed. The Cam Switch operation is transparent to the driver, who is simply rewarded with a smooth flow of power. Many older implementations only vary the valve timing (the amount of time per engine revolution that the intake port is open) and not the lift. Timing is continuously independently controlled to provide four optimized engine-operating modes:
MIVEC-MD
In the early years of developing its MIVEC technology, Mitsubishi also introduced a variant dubbed MIVEC-MD (Modulated Displacement), a form of variable displacement. Under a light throttle load, the intake and exhaust valves in two of the cylinders would remain closed, and the reduced pumping losses gave a claimed 10–20 percent improvement in fuel economy. Modulated Displacement was dropped around 1996.