Yamaha Unveils 425-hp V8 XTO Offshore Outboard
By Tom Richardson on November 11, 2020
Yamaha’s new four-stroke V8 XTO Offshore promises to be a game-changer in the world of big-boat outboard power.
The 425-hp, 5.6-liter V8 XTO Offshore delivers the thrust needed to push today’s big outboard boats and yachts. Boasting the first four-stroke powerhead in the outboard industry to use direct injection, the XTO Offshore sprays fuel at high pressure directly into the combustion chamber, rather than the intake track, just before the intake valve. This results in better fuel atomization and increases the effectiveness of the fuel burn for maximum power and efficiency.
The DI system employs five fuel pumps and raises injection pressure to 2900 PSI. The three-stage fuel-pressure system is aided by two independent fuel pumps within the Vapor Separator Tank (VST) that activate at specific RPM points. This ensures proper fuel flow and delivery, even at very high RPM.
The In-Bank Exhaust system features intake tracks that enter the cylinder head from both sides of the powerhead, allowing space for exhaust gases to have a more direct route to the lower unit and through the propeller hub.
Dual overhead camshafts on each cylinder bank are connected via a self-tensioning chain immersed in an oil bath for quiet, accurate valve timing and durability.
Carbon-coated shimless bucket-type valve lifters also increase durability, while the dual-chamber oil pump ensures proper oil flow and delivery at every engine speed.
Plasma fusion replaces conventional steel cylinder liners. The micro-textured surface is 60-percent harder than steel and significantly lighter, contributing to increased displacement without increasing the size of the powerhead. The resulting surface also increases fuel economy by decreasing internal friction.
The V8 XTO Offshore also features quad thermostats, two thermostats per cylinder bank, for improved flow and better regulation of engine and oil temperature.
The engine’s two-stage water pump features a massive rubber impeller for high pressure and flow, and a steel impeller that helps provide sufficient water volume even under the most extreme offshore conditions.
Extreme System Integration
The V8 XTO Offshore has integrated electric steering, the first of its kind in any outboard. The integrated steering system has no hydraulic lines or linkages, and delivers faster response over conventional systems.
The outboard also features an Integral Electronic Steering Control Unit that receives signals from the steering cylinder position sensor to carry out joystick and steering operation. Functions integrated into the electric steering system on Yamaha V8 XTO Offshore outboards include: joystick calibration, lever sensor, toe-in/out adjust, joystick thrust, lock to lock, and steering friction set.
Convenience & Control
Thanks to an ingenious new exhaust-gas relief system, V8 XTO Offshore propellers bite clean water in reverse, which helps yield reverse thrust up to 300 percent of that developed by Yamaha’s F350. That means easy maneuvering and more control when docking, particularly when the V8 XTO Offshore is matched with Yamaha’s Fully Integrated Boat Control System, Helm Master.
Boats powered by the V8 XTO Offshore need go no further than the dock for a lower-unit service, thanks to a unique gearcase lubricant exchange system that allows fluid changes while the boat is in the water. In addition, the V8 XTO Offshore also produces up to 90 amps of gross power, and reaches peak net output around 1500 RPM, where it is needed most.
Yamaha V8 XTO Offshore Highlights
- First four-stroke powerhead in the outboard industry to use direct injection
- Injectors spray fuel at high pressure directly into the combustion chamber
- Provides improved atomization and increased effectiveness of the fuel burn for maximum power and fuel efficiency
Unique Fuel System
- Five fuel pumps (3 electrical, 2 mechanical) keep fuel moving throughout the RPM band
- ECU-controlled variable fuel pressure—adjusted according to RPM and load—up to 2900 psi for outstanding atomization
- No-float Vapor Separator Tank (VST) with integral fuel cooler
3-Stage Fuel Pump System
- One lift pump and two independent fuel pumps within the Vapor Separator Tank (VST) activate at specific, individual RPM to feed two mechanical high-pressure fuel pumps
- Delivers proper fuel flow and delivery, even at extreme engine RPM
- 2:1 compression ratio (enabled, in part, by the piston cooling effects of direct injection)
- More “bang” from every spark
- Higher compression means better efficiency, more power and better throttle response
XTO OS Propellers
- XTO OS propellers are made to complement the torque potential of the Yamaha V8 XTO Offshore
- They work as part of a system to produce massive thrust in both forward and reverse, using diameters from 16 to 171⁄8 inches
- Increased blade surface area is designed for moving big boats and yachts
- Intake tracks enter the cylinder head from both sides of the powerhead
- Allows space for exhaust gases to have a direct route to the lower unit and out the propeller hub, improving flow
- Dual overhead camshafts on each cylinder bank are connected via a self-tensioning chain immersed in an oil bath for accurate valve timing and long life
- System provides quiet and precise connection for proper and consistent valve timing
- One-sprocket belt engagement means narrower, more compact overall profile with quiet operation
- Shimless, bucket-type valve lifters feature a tough carbon coating, reducing friction and increasing durability
Dual-Chamber Oil Pump
- Delivers proper oil flow and delivery at every engine speed
Plasma-Fused Sleeveless Cylinders
- Plasma-fusion is used in place of conventional steel cylinder liners
- Micro-textured surface is 60 percent harder than steel and significantly lighter and thinner
- Increases displacement without increasing size of the powerhead
- Also results in less friction, faster heat transfer, and increased fuel economy
Two-Stage Water Pump
- Massive rubber impeller produces high pressure and flow
- Steel impeller helps provide ample water volume under extreme conditions
- Proper cooling water flow at all RPM
- Improved temperature control
Integrated Electric Steering
- First of its kind in an outboard
- Electric motor directly moves and secures the outboard
- Fast, precise, responsive and leak-free
- Results in reduced power consumption, clean rigging, and a very orderly bilge area
In-Water Gear Lube Change System
- Allows draining and replacement of lower unit lubricant without having to remove boat from the water
- Easier maintenance at dramatically lower cost for large, in-water boats
Multi-part Cowling System
- Cowling and engine covers are integrated using captive fasteners and a special one-piece seal
- Allows easier access to specific parts of the powerhead and midsection, and further prevents water intrusion and the potential for corrosion
Engine Weight (Per Shaft-Length)