New Generation Yamaha offshore Outboards: Faster than a 2-Stroke?
 

Are Yamaha Outboard's new generation V6 motors stronger, lighter, quicker and smarter  than other outboards in their class?

Yamaha Outboard's new family of V6 offshore outboard motors are 246 pounds lighter than the V8 F300 it replaces and they weigh 51 pounds less than the previous generation V6 F250. That means the all new  4.2-liter F300 qualifies as the lightest outboard in its class paying big dividends in performance and vastly improved fuel  economy.  So how did Yamaha Outboards do it?
 

The horsepower boost was easy. The big-bore 4.2-liter  breathes  deeper than its predecessor thanks to a new  throttle valve that measure a 13-percent wider bore (75 mm) than the previous 3.3-liter four-stroke Yamaha. Intake valves measure 14-percent wider, while exhaust valves are  10-percent bigger. Air flow is voluminous. Camshaft timing is variable (electro-mechanical). Intake tracks have been lengthened for substantially stronger low-end torque.  Yamaha’s proprietary In Bank™ Exhaust system is renowned for the way it minimizes  back pressure to pump up  performance.

Beyond raw, bloody horsepower, the real question is exactly how did the engineers trim so many pounds from the savage beast? The answer is  new materials and processes. The build specs include plasma-fused sleeveless cylinders instead of conventional steel  liners set in an aluminum block. Plasma fused simply means an alloy dust, comprised of chrome, nickel, manganese and other elements, is super-heated in a plasma process and fused to the cylinder wall. Plasma fusion cuts 6.2 pounds of weight off the cylinder block and makes room for 2 mm wider cylinder bore (Bore and stroke build cubic inch displacement).

A real eyebrow raiser: This plasma fusion coating is 60 percent harder than mere steel and  very wear resistant. To the naked eye the plasma surface looks as smooth as glass, but it's  micro-dimpled. Its micro-texture surface (like the dimples on a golf ball)  better holds oil, reducing both wear and friction, which pays big dividends by way of a horsepower boost and better fuel economy. According to Yamaha Outboards, because the pistons pump up and down more freely, fuel economy measures 17-percent better than the nearest competitor.

Also important to note, plasma fusion shrinks  powerhead weight because the cylinder walls take up less space in the engine block than a conventional steel sleeve. Naturally it follows, that  frees-up room for wider-diameter pistons. In other words, there's more displacement shoehorned into the same space. Another plus, with plasma fusion, waste heat transfers more efficiently  between the  cylinder walls and the cooling system.

Weight saving measures include a  lightweight composite oil pan that's 61 percent lighter than its  aluminum counterpart. Being composite, a sheet molded compound, it doesn't corrode.

 Alternator output registers a whopping 70 amps, versus the previous Yamaha outboard's still ample  45 amps. And depending on whose numbers you crunch, that's 22 percent higher net amperage than the competitors. In spite of greater electrical output, the new alternator weighs six pounds less.  

I really like the new shift-dampener propeller hub  system that reduces the loud “clunk” often heard on larger outboards when shifting into gear. Finally, the new generation Yamaha outboards are  available in  25” and 30” shaft lengths  as well as left and right-hand configurations.  © Copyright 2009 by Tim Banse

The new Yamaha outboards weigh 246 pounds less than the previous model Offshore F300 founded upon a 5.3-liter V8 powerhead.

Yamaha offshore outboards boast a three-star rating for ultra-low emissions  from the California Air Resources board (C.A.R.B.) and meet,  or exceed, all Federal exhaust emissions requirements.