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Yamaha Marine VMAX SHO 150 Horse

Brute Strength and Exemplary Fuel Efficiency

Back in the day when 4-stroke outboards first hit the water, compared to competing 2-strokes, they were heavier and mildly anemic at lower rpm. That's changed to the point where today' 4-stroke outboards perform as well and in some cases even surpass 2-stroke outboard performance. A good example is Yamaha Marine's V MAX SHO 150 hp. outboard.

Yamaha VMAX SHO 150

With its HO (High Output) moniker you already know Yamaha's Max SHO 150 scorches the water. Good to know, beyond brute strength the powerhouse 4-stroke outboard also runs clean, quietly and with boasts exemplary fuel efficiency. And thanks to a flat torque curve, acceleration is strong enough to send a delightful shiver up and down your spine. How do we know this? In the relentless pursuit of truth we caught a flight to Yamaha Marine' test facility on the banks of the Tennessee river where we test drove a number of boats rigged with the new engine. Then after lunch we sat in on a technical briefing outlining exactly how the engineers made this engine come to life. So what did we learn on the water and in the class room?

Let's start at the beginning. V MAX SHO 150's 2.8-liter four-cylinder powerhead swings double overhead camshafts that open and close four-valves per cylinder. Four small valves as opposed to two bigger valves keeps intake and exhaust velocity high at the same time it flows a big volume of CFM in and out of the combustion chamber. High port velocity improves low end response.

But what really works the magic is Yamaha's Variable Camshaft Timing System. Without bogging down into details suffice it to say VCT changes relative to Crankshaft Top Dead Center when the camshaft begins to open the intake valves. Advancing or retarding pays big dividends in throttle response in the low- and mid-rpm ranges, significantly speeding acceleration. And once again, compared to two-strokes, fuel economy is 30- to 40-percent better.

Curious to learn VCT mechanical details? The camshaft sprocket has two oil-filled chambers. The ECM sends oil to one or the other depending on load and engine rpm, causing the sprocket to traverse either clockwise or counter-clockwise (within a 20 degree range). Opening the intake valves early improves low end torque while retarding improves high rpm power. Some experts claim VCT is like having both a torque cam and a racing cam all in one.

Beyond raw bloody performance V MAX SHO 150 is light weight, tipping the scales at 480 pounds, or just about the same curb weight as a comparable 2-stroke. Now add on the 2-stroke oil tank and the weights are about equal, plus you can take advantage of the space given up by the oil tank. Another amenity is the 50-amp alternator good for powering a boat's many electronic gizmos.

You're probably wondering about rigging a new boat or re-powering with this engine. V MAX SHO 150 is designed to be rigged with mechanical controls for easy use with most bass, bay and flats boats. As for instrumentation, the Yamaha engine talks to analog, 6Y5 digital or Command Link gauges and can easily be rigged to external NMEA 2000 compatible displays. More good news, Yamaha's V MAX SHO Series of propellers are graduated in single-inch pitches for more precise finely-tuned performance. One must have option is the Y-COPA theft deterrent system.

And finally, normally we don't talk about curb appeal in outboard motor evaluations. But the V MAX SHO 150 merits special notice. She looks fast even at idle. She sure is good looking. At the dealer showroom take notice of the special paint scheme and flashy decals. If you have even an ounce of motor oil coursing through your veins your heart will begin to go pitter patter. Then, out on the water, running the engine, feeling the WOT vibration massaging the soles of your feet and hearing the reciprocating mass singing its siren's song, surely you will be hooked.

Author Timothy Banse has published articles in Popular Mechanics, All Chevy, Pickup Van & -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.

Yamaha Marine VMAX SHO 150
Cylinder Block Configuration InLine-4
Displacement 163 CID
2.8 Liters
Bore x Stroke 3.78" x 3.79"
Horsepower 150 @ 5500 rpm
Operating range 5000-6000 rpm
Compression ratio 10.3 to One
Gear ratio 1.86 - one
Weight 480 pounds

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