Engines from Mercury, Yamaha, Volvo Penta and others that are mentioned in this month’s propulsion roundup are equipped with some form of technology that increases mid-range performance and acceleration. One of those technologies is variable valve timing. So what is VVT?
David Meeler, Yamaha’s marine product information manager, likens variable valve timing (Yamaha’s version is called variable camshaft timing, or VCT) to a weightlifter’s breathing technique. “A weightlifter takes a deep breath before hoisting the barbell to feed his muscles for maximum exertion,” Meeler says. “Variable camshaft timing works in the same way — it helps the engine breathe sooner and gets the fuel-and-air charge into the combustion chamber faster, based on the load and throttle demand on the engine. At least ours does — everybody has their own tweak on it.”
But the concept is the same: immediate on-demand combustion through faster and more efficient use of air and fuel, Meeler says. The engine has greater “grunt.”
It all starts when the operator hits the throttle, and the key is the quick syncing of two engine sensors — the throttle position and crank position sensors, Meeler says. “When you throw down the hammer, the electronic control module — the brains of the operation — takes note of the fully opened throttle plate and the slow rotation of the crank position sensor, which monitors engine rpm. It then tells the engine it needs to make a bunch of power fast to help the CPS catch up with its brother. And it does this in a nanosecond.”
The intake camshaft rotates, the valves open sooner, the exact amount of fuel and oxygen enter the combustion chamber faster, and “bang, away you go,” says Meeler.
You notice the technology most in the middle of the rpm range. “It’s that midrange punch from about 2,500 to 4,000 rpm,” he says. “If you are running at 3,000 rpm and punch the throttle, you will feel the engine pin you back in the seat.”
Mercury and Volvo Penta engines also pack that same kind of mid-range punch. I have felt it while operating Mercury Verado outboards, such as the 300-hp model, and sterndrives from MerCruiser and Volvo Penta. The first Yamaha engine with it was the 3.3-liter F250, which was released in 2006 and followed about a year later by the V8 F350. Now the technology can be found on Yamaha engines from 150 to 350 hp.
Can you actually see and touch components that make the technology work? You bet, Meeler says. Yamaha’s system comes on most dual-overhead-cam outboards, whether inline or in a V-type configuration. A special device on top of the intake cams manipulates them to open and close the valves for air and fuel intake.
Variable valve timing’s immediate throttle response boosts the fun factor in driving a powerboat, no doubt, but it also can help on the safety side. “Picture yourself in rough seas, climbing waves,” Meeler says. “That acceleration, that immediate throttle response can help provide better control of the boat.”
This article originally appeared in the June 2014 issue.
