America's Definitive Marine Engine Magazine
Potent performers, this V-6 big block displacement builds lots of low end torque, in fact, more than enough acceleration to compete head to head with 2-stroke outboards.
Yamaha's VMAX SHOs are a family of four-stroke outboard motors available in 250, 225 and 200 horsepower. Yamaha VMAX SHO 's torque curve is as flat as the Kansas prairie which builds big power at low end and also all the way up and down the operating range, and especially in the mid range. Bump the throttle and there 's plenty of power in reserve. Popular on bass boats, these marine motors also find a happy home rigged on the transom of pontoon and deck boats.
VMAX SHO is founded upon all-new 4.2-liter V-6 powerhead that employs material component parts and manufacturing processes that make the outboard motor lighter, more efficient and powerful. A good example is the throttle valve: It measures 13-percent larger in diameter than the butterfly valve found on previous 3.3-liter four-stroke Yamaha V-6. The net result: Freer breathing that builds in turn more horsepower at Wide-Open Throttle. The cylinder head is populated by large diameter intake and exhaust valves actuated by Variable Camshaft Timing. VCT, depending on engine rpm and load, either retards or advances (relative to crankshaft Top Dead Center) when the valves being to open. Then to pump up low end torque intake air flows down through long, tuned intake tracks. On the exhaust side Yamaha's In Bank Exhaust system reduces back pressure and improves performance.
Instead of conventional steel cylinder sleeves the cylinder block is fitted with plasma-fused, sleeveless cylinders, a bearing surface that 's 60-percent stronger than mere steel. Some industry experts claim wear is half that of a conventional cylinder It gets even better. The plasma coated/micro textured cylinder walls dramatically lessen friction, reducing parasitic power losses and paying big dividends in sharper acceleration and improved fuel economy. Yamaha claims 12-percent better fuel economy when compared to competitive 2-stroke outboards.
And because the plasma coat process takes up less space in the engine block than a conventional steel sleeve there is more room for the pistons themselves. In other words they can be bigger. The wider bore calculates to a bigger Cubic Inch Displacement but in a small envelope. And because the sleeveless cylinders transfer combustion heat more efficiently between the cylinder walls and the coolant (because they are thinner),cooling is more efficient. VMAX SHO's high-performance lower unit water pickups are a jaw-dropping 81-percent larger than previous VMAX outboards.
Besides helping to build raw, bloody, horsepower the plasma-coat process reduces weight, this 4-stroke outboard is 34 pounds lighter than its two-stoke predecessor. The cowling is an advanced composite that 's 14.6-percent lighter than a fiberglass cowling. The transom mounting bracket was engineered to be lighter weight, yet sturdy. Designed for bass and flats boat applications, it 's 29-percent lighter than the bracket used on the its predecessor. The engine pan, fabricated of lightweight composite, is 59-percent lighter than an aluminum counterpart and provides greater protection against corrosion. Finally, the VMAX is protected by Yamaha's three-year limited warranty, for pleasure use.
|Yamaha VMAX SHO||VF250|
|Cylinder Block Configuration||V-6 (60 deg)|
|Bore x Stroke||3.78" x 3.78"|
|Horsepower||250 @ 5500 rpm|
|Operating range||5000-6000 rpm|
|Compression ratio||10.3 to One|
|Gear ratio||1.75 to One|
Author Timothy Banse has published articles in Popular Mechanics, All Chevy, Pickup Van and 4-Wheel Drive, Mecanica Popular, Motor Boating, Yachting, Mar y Vela and many other magazines and newspapers from around the world. He writes about cars, trucks and tow vehicles and marine-engine technology.