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What is Variable Valve Timing?

For the sake of efficiency, car engines automatically retard and advance ignition timing according to acceleration and load. In the past, this was accomplished via vacuum controls, but now, it's done by engine computers. For many years, it's been known that controlling exhaust and intake valves in similar ways would reduce emissions, boost fuel mileage, and enhance power. Here from  Marshall Motors Auto Repair Service Center at Salina, KS you'll learn what variable valve timing is and how it helps your engine run more efficiently.

Variable Valve Timing Systems

Camshaft lobes are oblong and only touch the rocker arm or lifter for a certain duration, with each lobe lifting the valves a set amount. Because the engine's valves open twice on each intake, compression, power, and exhaust cycle, the camshaft only spins half as fast as the crankshaft. Cams designed for higher lift and longer duration perform well at higher RPMs, and that's why race-ready vehicles don't do so well on city streets. The perfect scenario is to find a valvetrain that can be adjusted for lift and duration according to load and engine RPMs. Engineers began to experiment with VVT or variable valve timing setups in the 1960s, but they didn't really make it to the market until the end of the 1980s. There are a few VVT types:

• Cam switching, which affects duration and lift with different cam profiles. It's much like having two camshafts for different engine RPMs.
• Three-dimensional cam lobes: Rather than being oblong, these are long and tapered. Here, the camshaft moves back and forth in the head so different parts of the lobes touch the rocker arms for changes in duration and lift.

VVT Controls

Even the best VVT system is useless without input from the engine computer, which uses readings from the cam position sensor and crankshaft position sensor to adjust load and RPMs. The VVT system's actuation is accomplished through oil pressure changes via switches, solenoids, and oil galleys. While we're on the subject of oil, it's important to change the oil at recommended intervals, as the VVT system's solenoids are easily damaged by poor lubrication.

More Accessible and Affordable

Variable valve timing systems are intricate and they increase the cost of engine construction and design, but like most new technologies, it's becoming more cost-effective and reliable with each generation. There's one thing for sure, though: VVT pays off in the form of increased power, better fuel economy, and improvements in emissions control.

 Marshall Motors Auto Repair Service Center, 3500 S 9th Street, Salina, KS 67401

Sources: Wikipedia and Popular Mechanics