yamaha 4stroke meets challenge of 2stroke boat motor

Conventional wisdom says that to build a 4-stroke outboard engine in the 200-horsepower range, it must be heavier and larger in displacement than comparably powered 2-stroke marine motors. Not so, claim Yamaha engineers. But, yes, it does require changes in conventional thought.

Yamaha engineers feel that they have met the challenge of creating an environmentally more friendly performance outboard that can compete head-to-head with similarly powered two-stroke motors commonly seen on the transoms of bass boats and other high performance watercraft.

Yes, in general, a 4-stroke motor by its very nature has more moving parts than a two-stroke and traditionally requires greater displacement to achieve the same power of a comparable two-stroke. Still, Yamaha engineers took on the challenge of designing a 4-stroke outboard in the popular 225 horsepower class that would be comparable in size and weight to popular two-stroke engines already on the market.

First, the engineers retooled their thinking. This led them to reverse the conventional four-stroke layout for intake and exhaust systems by tucking the exhaust into the V-shape of the marine-specific design. The 60-degree V6 engine needs to be a high performer like a 2-stroke. The "in-bank exhaust system" design reduced exhaust resistance compared to conventional designs.

Electronic fuel injection with inside-track fuel injectors were positioned on the inside walls of the "pulse-tuned long intake tracks" running along the outside of the cylinder block. The electronic controls of the fuel injection system optimize combustion to boost torque and power. Bottom line: the Yamaha F225A has shown it can out-accelerate competitive 225-hp two-strokes from a standing start to the first 50 meters.

The advantages of the new 4-stroke include a 20 percent gain in fuel efficiency versus a two-stroke. Plus, the engine meets emission regulations for 2006. And, don't forget that the new motor is also a quieter runner than its comparably powered two-stroke competition.

So, if Yamaha can do this with a bass boat engine that must meet expectations of an owner's group that is similar to snowmobile owners, can the Yamaha engineering staff placate sledders, too? Just a thought and update on what's going on in other sports.