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==