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Putting Yamaha to the test

Two new Yamaha four-stroke outboard engines get a real-world workout during a press introduction in the Florida Keys

Where boating performance is concerned, weight is the enemy. Anything you can do to lighten your load—bring less gear, uninvite an annoying crew member, shed 20 pounds of fat—will help your boat run faster. In the world of outboard engines, where four-stroke power is becoming standard, shedding 20 or 40 pounds off an engine’s weight is a big deal. Flat-bottom fishing boats—such as bay, bass and flats boats—are weight sensitive yet can require up to 250 horsepower to perform at their best. Yamaha found a way to cut 34 pounds off its previous 250-horsepower four-stroke motor, and introduced the new 250-hp VMAX SHO in June during a press event at the Hawks Cay Marina on Duck Key. Yamaha also announced it is now shipping the new 70-hp F70 four-stroke engine introduced at the 2010 Miami International Boat Show.
Yamaha says the VMAX 250 SHO’s 505 pounds is lighter than any two- or four-stroke production V6 fishing outboard of equivalent horsepower.
“With the VMAX SHO, Yamaha has done what everyone said couldn’t be done,” said Ben Speciale, Yamaha Marine Group president. “We have a four-stroke that out-performs two-strokes in many ways and provi des best-in-class acceleration.”
Yamaha teamed with Pathfinder to create an ideal platform for the new 250-hp VMAX SHO (Super High Output) engine. Pathfinder’s new 2300 HPS (High Performance Step) fishing boat was built from scratch specifically around the new 250 VMAX SHO. “The 2300 HPS is purpose-built for the angler who wants to get to a spot before anyone else,” explained Skip Lyshon of Pathfinder. “It’s a fast boat out of the hole and at top end due to the bottom design (a high-performance step amidships) and the power of the new VMAX SHO.”
During testing Lyshon found the boat ran its best top-end speed of 65 mph spinning a four-bade Yamaha 21-inch pitch propeller—not the recommended propeller set up from Yamaha, but Lyshon said prop performance can vary depending on the trim and jackplate settings. Running at 35 mph, the engine burns just 4.2 gallons per hour.
Yamaha’s own testing shows the VMAX SHO is faster out of the hole and to plane than the Yamaha VMAX Series 2, and has a broader power curve for smoother acceleration and performance.
“One of the most impressive things about the VMAX SHO is its midrange punch,” said Speciale. “Whenever you push the throttle forward, there’s power to spare.”
An all-new four-stroke 4.2-liter V6 powerhead provides the best power-to-weight ratio in its class. With more displacement than its competitors, the 4.2-liter employs new materials and processes that help make it lighter, more efficient and powerful. The powerhead utilizes plasma fused sleeveless cylinders instead of steel sleeves to provide a durable surface for the piston rings. That reduces the overall powerhead weight and takes up less space in the engine block than a conventional steel sleeve, making more room for the pistons themselves and optimizing the displacement advantage.
The process has allowed Yamaha engineers to gain the greatest displacement from the least amount of mass in the engine block, which also reduces overall weight. At the same time, it yields a surface that is 60 percent stronger than a steel liner for greater durability. In addition, the sleeveless cylinders result in better heat transfer between the cylinder walls and the cooling system, meaning more efficient cooling.
Other weight-saving improvements include the VMAX SHO’s lightweight cowl. Made of an advanced composite, it is nearly 15 percent lighter than a cowl made of typical fiberglass.
The other big news from the press event: Yamaha Marine is shipping its new four-stroke F70 outboard, which can be used in applications formerly reserved for older technology carbureted two-stroke outboards. At the press event, two flats boats were powered by the F70: Maverick’s 17HPX Tunnel and Sundance’s FX17. During test drives both boats had plenty of power from a standing start, and good top-end speed.
The new F70 weighs 109 pounds less than Yamaha’s four-stoke F75, and Yamaha’s engineers found plenty of places to shave off weight. First is the unique four-cylinder, single overhead cam, four-valve-per-cylinder design. Most powerheads that employ four-valve-per-cylinder designs do so using two cams, one for each pair of valves on either side of the cylinder head. The F70 four-valve-per-cylinder powerhead uses a single cam design, saving weight and reducing parasitic losses associated with the friction of turning an extra cam. The four-cylinder design gives the powerhead 17 percent more intake valve area, which improves efficiency.
Combined with up to 10 percent lighter pistons and valves, compared to those in similar powerheads, and you get a higher rpm operating range (5,300 to 6,300) and greater power and speed.