Some of the engines from Mercury, Yamaha, Volvo Penta and others that are mentioned in this month’s propulsion roundup are equipped with technologies that boost midrange acceleration and performance. One of those technologies is variable valve timing.
David Meeler, Yamaha marine product information manager, compares variable valve timing — Yamaha’s is called variable camshaft timing, or VCT — to a weightlifter’s breathing. “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. Every [manufacturer] has their own tweak on it.”
VCT delivers 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. 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, an exact amount of fuel and oxygen enters the combustion chamber faster, and “bang, away you go,” says Meeler. “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.”
The first Yamaha engine with VCT was the 3.3-liter F250, which hit the market in 2006. The V-8 F350 followed about a year later. Now the technology can be found on Yamaha engines from 150 to 350 hp.
Mercury and Volvo Penta engines also pack a midrange punch. I’ve felt it while operating Mercury Verado outboards, such as the 300-hp model, and sterndrives from MerCruiser and Volvo Penta.
Verado engines don’t use variable valve timing. The outboards gets midrange performance from a supercharger with electronic boost control, says Mercury Marine senior category manager Steve Miller. A computer controls the amount of boost applied based on where the operator sets the throttle, he says. “If the operator is cruising along and suddenly punches it, the computer tells the boost bypass valve to close, instantly creating the additional boost to set you back in your seat,” says Miller.
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.
It’s fun to operate engines with such quick throttle response, 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.”
See related article –
New outobards, sterndrives and integrated systems
July 2019 issue
