The wraps are off the new Yamaha XTO Offshore outboard platform. The all-new outboard, rated at 425 HP, features a 5.6-liter V8 powerhead with direct fuel injection. The XTO sets a new benchmark for displacement and power from Yamaha.

The XTO Offshore, which in Yamaha-speak is called the XF425, will be available beginning in August, and will be sold alongside the Yamaha F350C outboard model, which will remain in production. Note, however, that according to Yamaha the XTO Offshore 425 produces 150 percent more thrust than the F350. This is a new level of performance from Yamaha.

Searching for big outboard power for a hardcore offshore fishing boat? Yamaha has delivered with the XTO platform.

The XTO Offshore is designed with an eye to growing demand for outboard power for the heaviest offshore fishing boats, dayboats and even pontoons—“massive power for 50-foot plus boats,” according to Yamaha. The new XTO platform is designed first and foremost to deliver a mountain of torque that reportedly peaks at 400 ft. lbs. at 4500 rpm. Everything about this motor is robust and heavy-duty to the point of appearing to be over-engineered for current applications. But that’s just Yamaha anticipating the future duty this big outboard could see.

“The F350 outboard taught us that outboard-powered boats could grow a lot bigger,” said Yamaha Marine President Ben Speciale. “To push a bigger boat we need to start with a bigger propeller. And to turn that propeller, a lot more torque.”

Yamaha really started designing the XTO at the prop, specifying the blade area required to push and lift heavy boats and also to function well with its Helm Master joystick system. The new line of three-blade stainless XTO OS props range from 16 inches to 17.125 inches in diameter with a 15- to 25-inch pitch range in two-inch increments. All XTO OS props feature the Yamaha SDS (Shift Damping System) hub. On average, the XTO OS props offer 14 percent more blade area than the Saltwater Series XL props designed for the F350, and 28 percent more area than the Saltwater Series II props designed for the F300 model motor. Yamaha told us that four-blade XTO props will be available in the future.

yamaha XTO offshore outboard

Yamaha's new XTO outboards are surprisingly heavy, but are designed to seamlessly integrate with Helm Master and other boat systems.

The powerhead design starts with the generous 5.6-liter displacement from a perfectly square 96 x 96mm bore x stroke, a combination skewed toward torque rather than high-rpm horsepower. Double overhead cams control four valves per cylinder. The intake cams feature variable timing to broaden the powerband. The 60-degree engine does not require a balance shaft. The elevated 12:1 compression ratio should further boost torque output. The WOT rpm range is a modest 5000-6000.

The XTO will be the first mass-production four-stroke marine engine to feature direct fuel injection. DFI is of course the technology behind low-emissions two-stroke outboards offered by Mercury Marine, Evinrude and Yamaha. In a DFI system fuel under very high pressure is injected directly into the combustion chamber rather than into the airflow along the intake tract. Yamaha says the fuel system on its XTO V8 requires five separate fuel pumps and reaches 2,900 psi at the injector nozzle. The high pressure is required to both atomize the fuel into particles small enough to burn efficiently and to complete the injection process in the fraction of a second available at 6000 rpm. DFI for four-stroke engines has been widely adopted by the automotive industry. Its benefits include lower exhaust emissions, improved fuel economy especially at low speeds, and the ability to perfectly match fuel delivery to engine load. The mixture can be rich on hole shot to improve torque production, leaned out at cruising speed for better economy, and rich at wide-open throttle for maximum power and to keep the pistons cool—which is how Yamaha controls detonation with a 12:1 compression ratio. Yamaha does spec 89 octane fuel for the new XTO. Yamaha says DFI helps the new XTO outboard deliver 5 percent to 10 percent better cruise-speed fuel economy than the F350, and up to 12 percent better economy at wide-open throttle, while producing more power.

The XTO cowl comes off in pieces, but only the top is not secured with fasteners. Removing the top provides access for oil check/fill and basic inspection.

Electrical charging power is almost as important as torque on big angling boats. The XTO alternator is rated at 90 peak amps, with 58 amps net available at idle and 72 amps net at just 1500 rpm. On a boat with quad XTO outboards, that adds up to 288 amps of charging power at trolling speed. You could almost weld. Or at least run a boat-load of accessories for hours while trolling without the need for a generator to keep the batteries charged. Because heat diminishes charging output, the lighting coil on top of the engine is cooled with forced air from a dedicated fan and a vent—which looks like a scoop on the top of the cowl—that directs the heat away from the powerhead.

The gearcase is all new, with a shape Yamaha says is its most hydrodynamic design ever. The case has four large cooling water intake ports that feed a two-stage water pump. The first water pump has an automotive-style metal impeller, while the second has a rubber impeller. To hold bigger, stronger gears the case diameter is 6 inches, compared to 5.25 inches for the F350 and 4.75 inches for the F300. The gear ratio is 1.79:1. Propshaft diameter is 1.5 inches at the bearing and 1.2 inches at the splines. The gearcase lube can be drained with the boat in the water, using a vacuum pump connected to a fitting on a line alongside the powerhead. So in theory these motors can be serviced with an oil and lube change at the dock.

A new exhaust relief system is designed to improve prop thrust performance in reverse. At idle exhaust exits through a familiar relief port on the midsection. At greater throttle settings, up to about 2500 rpm, exhaust exits through a set of vents located above the anti-ventilation plate. With no exhaust exiting at the prop hub, the prop bites clean water for significantly improved thrust in reverse. When engine speed exceeds 2500 rpm, exhaust overcomes water pressure and exits through the prop hub. Yamaha says the XTO 425 produces 300 percent more reverse thrust than its F350C model. This is a benefit with or without a joystick control, but the advantage is huge with multi engines and a joystick, as thrust is better balanced between motors operating in forward and reverse gear.

This XTO cutaway shows stout drivetrain components and exhaust routing. Under moderate throttle, exhaust exits through six ports about the anti-ventilation place and does not foul the prop in reverse gear.

I felt torque and thrust in abundance during two short test drives of the XTO 425 at the Yamaha testing center on the Tennessee River in Alabama. The most impressive performance was a quad rig on the new Grady White Canyon 456, a 45-foot, 35,000-pound boat that popped on plane like a lightweight bay skiff with 1,700 HP and what felt like an acre of blade area on the transom. Top speed was 58 mph at 5900 rpm. I also ran a twin-engine rig Grady White Canyon 336 (33 feet 6 inches and about 13,000 pounds as tested), which also planed off effortlessly. After running up to a top speed of 55 mph, I throttled back to 4500 rpm and with the motors still set at about three-quarter trim, put the boat into a moderately aggressive 180-degree turn. I didn’t need to touch the throttle to keep the boat on plane and there was not a hint of prop slip. The big XTO props stayed hooked up. Impressive. Hard hole-shot acceleration is likely not a priority for most owners of wide-beam off-shore boats, but the combination of abundant torque in the middle of the rpm range and the grip of big props will be ideal when climbing and cresting ocean swells, or holding plane in rough seas at lower speeds.

Quad Yamaha XTO Offshore 425 outboards pushed the 35,000-pound Grady-White Canyon 456 to 58 mph and made it handle like a dream.

I was surprised by the sound level produced by this new motor. Aboard any recent Yamaha-powered boat the sound level of the motors is so low as to be hardly discernible at cruising speed. The XTO seems to be a little loud at 4000 rpm, but the sound level picks up at 4500 and becomes really distracting at 5000 rpm, with a raspy tone. Granted, I was on multi-engine boats and one has an enclosed house at the helm that could reflect back noise. But I was not the only one at this preview for the media who commented on engine noise. Yamaha didn’t have much to say when I asked about the sound level, except that this is a powerful engine that needs to flow a lot of air. So there you go.

The Yamaha XTO is designed to integrate seamlessly with Helm Master and other boat systems. The electric power steering system is truly “drive by wire” and integrated into the engine; there’s only a wire from the electronic helm to the engine and no hydraulics in the boat or on the motor. The steering system is contained in a tube-shaped device on the front of the outboard and uses a ball-and-screw system similar to that used on many autos and trucks. Yamaha says the electric system weighs 38 pounds less than its electro-hydraulic systems and saves a lot of space in the transom. The steering ratio and friction are both adjustable. Like other large Yamaha outboards the XTO 425 rigs on 28.5-inch centers for multi-engine installations, and the mounting bolt pattern is the same as that of the F350. The XTO has 73 degrees of tilt range and should tilt completely out of the water in most installations.

Electric power steering system is contained in the large cylinder on top of the mounting bracket.

The XTO will be available in 25-, 30- and 35-inch lengths. That 35-inch length is new and I believe a first in the outboard market. Yamaha says it will allow bigger boats to maintain a flat (rather than cut-down) transom and get the center engine prop in the water. Published dry weight ranges from 952 pounds to 999 pounds. These are surprisingly heavy outboards. The new Mercury 4.6-liter V8, rated up to 300 HP, weighs 600 pounds in Verado trim, and a Mercury Racing Verado 400R that likely makes an honest 440 HP, weighs less than 700 pounds. The 5.3-liter V8 Yamaha F350 weighs 763 pounds in its 25-inch size. It should be noted that the weight of the electric steering system is included with the overall weight of XTO. Separate steering components are not included in the weight of other outboards. Yamaha does not seem to be concerned at all about the weight of the XTO, pointing out that as a percentage of total boat weight it’s not that significant. Which I guess is true. Think about it this way – does a farmer care about how much his new John Deere tractor weighs? No. He cares about its power and technology. The Yamaha XTO is a tractor for the water.

The Yamaha XTO can be ordered with no paint for owners who want to apply a custom finish. Graphics are shipped with the motor.

There will be a XTO Offshore 375 model for some markets but it will not be offered in the United States. The new motor will be available in white or gray colors, or unpainted and ready for custom paint jobs. The standard warranty is five years. The MSRP pricing rages from $44,750 to $46,120 for a grey or unpainted motor. White paint is about $500 extra, and left-hand rotation adds about $935.

Written by: Charles Plueddeman
Charles Plueddeman is's outboard, trailer, and PWC expert. He is a former editor at Boating Magazine and contributor to many national publications since 1986.