Yamaha’s Biggest Outboard Yet — the 5.6L V8 425 XTO

New engine features 12.2-to-1 compression, direct injection, electric steering

Footage by Chris Woodward and courtesy Yamaha

Yamaha's all-new 5.6L V8 425 XTO, the most powerful outboard from this company since the F350 debuted in 2007, brings to market several firsts — from direct injection to electric power steering. Yamaha says its engineers rethought the outboard engine from the prop up to propel today's large center-consoles and expresses.

“This is an integrated outboard system, designed to push the heaviest offshore boats and yachts,” says Ben Speciale, Yamaha Marine Group President. “The new Yamaha V8 XTO Offshore has 5.6 liters’ tremendous thrust and 425 horsepower.”

Yamaha 425 XTO Offshore Outboard Engine
The 425 hp XTO is available for single, dual, triple and quad configurations.Courtesy of Yamaha

Here are some of the highlights Yamaha related to boating media about the new XTO during its debut in late May:

• First fourstroke powerhead in the outboard industry to use direct injection. Fuel is sprayed at high pressure directly into the combustion chamber rather than the intake track. This improves atomization and increases the effectiveness of the fuel burn.
• The direct-injection system features five fuel pumps and injection pressure up to 2,900 psi. The three-stage fuel-pressure system is, in part, composed of two independent fuel pumps within the Vapor Separator Tank (VST) that activate at specific, individual rpm. This ensures proper fuel flow and delivery, even at very high engine rpm.
• Highest compression ratio in an outboard at 12.2-to-1. That means more bang from every spark as well as better efficiency and power (enabled in part by the piston-cooling effects of direct injection).

Yamaha 425 XTO Offshore Outboard Engine White
The V8 425 comes in white, gray or unpainted. The electric steering unit resides in the cylinder just below the front of the powerhead.Courtesy of Yamaha

• The XTO comes with integrated electric steering. So, there are no hydraulic lines or linkages. Yamaha says this system responds more quickly than conventional systems to steering inputs.
• XTO OS propellers range in diameter from 16 to 17 1/8 inches, offering increased blade surface area for moving big boats and yachts.
• In addition to an oversized gear case, hardened gears, and a robust, offshore bracket and motor mounts, the V8 XTO Offshore outboard also has a two-stage water pump and dual-chamber oil pump, each designed to respond to heavy loads.
• Spark plugs are made from the rare element iridium, to improve throttle response and economy, increase service life and improve power.
• The XTO comes with quad thermostats, two per cylinder bank. One pair helps regulate engine temperature; the other helps regulate oil temperature.

Yamaha 425 XTO Cowling
The 425's cowling was designed in parts to facilitate maintenance.Courtesy of Yamaha

Yamaha credits its new exhaust-gas relief system for energizing the XTO in reverse, generating up to 300 percent more thrust than the company’s F350. Shift into reverse, throttle back and the boat accelerates quickly as water crests the top of the transom bulkhead. Exhaust is diverted away from the XTO’s big props below 2,500 rpm, meaning the blades bite clean water.

Yamaha designed the new cowling for the outboard in several parts to make it easier to access to specific areas of the powerhead. A unique gearcase-lubricant exchange system allows fluid changes while the boat remains in the water.

Engineers also increased the engine tilt range up to 73 degrees. The outboard extends 5.6 inches higher out of the water than the F350; the entire motor and lower unit can be raised completely out of the water.

Yamaha 425 XTO Offshore Outboard Engine Gray
Yamaha's new V8 was designed from the prop up to push big center-console and express boats.Courtesy of Yamaha

The XTO will be available in gray, white, or unpainted (for color customization by a boat builder), and in 25-, 30- and 35-inch shafts. Retail pricing will start at $44,000. Yamaha also upgraded its Helm Master features and its CL7 display for the XTO.

SPECIFICATIONS:
ENGINE
Type............................................................ 4-Stroke, DOHC V8 - 32 valves Displacement............................................... 5559 cm3
Bore x Stroke............................................... 96.0 x 96.0 mm
Full Throttle RPM Range.............................. 5000 – 6000
Variable Trolling RPM Range......................... 600 – 1000 RPM
HP Rating at Propshaft................... 425hp @ 5500 RPM
Compression Ratio....................................... 12.2:1
Fuel Induction/Scavenging...........................DOHC, DI, 4 Valves per Cylinder
Alternator Output......................................... 90 Amps Gross, Max
Starting Method........................................... Electric w/ PTT
Ignition........................................................ TCI Microcomputer
Lubrication..................................................Wet Sump
Degree of Trim............................................. -4° through +16°
Degree of Tilt............................................... -4° through +73°
Exhaust....................................................... Through Propeller (Except in Reverse Under 2500 RPM)
Cooling........................................................Water, Thermostatic Control
Steering....................................................... Integrated, Electric Actuation

DRIVE
Gear Ratio.................................................... (25/14) 1.79
Control Method............................................ Digital Electronic Control

SHAFT LENGTH
See Model Code........................................... X = 25", U = 30", E = 35"

FUEL AND LUBRICATION
Recommended Fuel...................................... Regular Unleaded (Minimum Pump Octane 89)
Recommended Oil........................................ Yamalube Marine Lower Unit Gear Lube HD
Engine Oil Capacity...................................... 7.8L / 8.2 U.S. Quarts (with filter) 7.5L / 7.9 U.S. Quarts (without filter)

LIMITED WARRANTY
Pleasure...................................................... Five Years Government................................................. Three Years Commercial................................................. One Year

WEIGHT
XTO 25" = 432 kg / 952 lbs, XTO 30" = 443 kg / 977 lbs, XTO 35" = 453 kg / 999 lbs

*Weight estimated at time of publishing. Weight is measured without motor oil, gearcase oil and propeller.