Yamaha 350 V8

Yamaha Top Gun

The creep in available horsepower has been escalating in outboard manufacturing circles since that early year when Ole Evinrude first patented his outboard motor and one wonders when it will hit its ceiling. Perhaps it won't.

If we follow the US trend (and we normally do in this country) there will be a radical change in the style we power larger vessels. Particularly in the United States, the trend is to fit larger and more outboards to boats in order to do away with inboard installations that gobble up cockpit space and to alleviate the issues involved with transom leg setups. As you read this, the triple rig outboard configuration is evolving in Oz with talk already circulating around the traps of quad rig installations on vessels of 9 metres-plus for specialised purposes.

The most recent addition to the line-up of big guns is that from Yamaha with the first V8 outboard on offer anywhere in the world.

This power plant is aimed squarely at big boats such as those in the eight-metre-plus range including those used by the commercial industry such as oyster farmers who run high-speed barges many of which are twin-rigged with 115 to 250hp motors.

The low gearbox ratio in the new V8 of 1.73:1 will allow it to spin propellers to 25in providing plenty of torque and power for serious-work platforms.
One would think that the bulk of eight cylinders would make the powerhead and cowl over-width but Yamaha have retained the 60º vee of the 250hp models and added two cylinders to the height of it. They then installed the dual exhaust chambers in the vee of the block to keep it compact.

SUPER ENGINE
The super-engine has a displacement of 5.3lt which equates to power-plus in the 'grunt' department and the manufacturer is claiming 45 per cent more thrust than their 250hp models. That is a big call but they have catered for it in the strength of the build of this engine with forged engine mounts and oversized mounting brackets which provide the already stated but also help reduce noise and vibration. They have also designed the transom mount to have six bolts through the stern rather than the usual four.

With so much happening under the cowl a new-style water-cooling system has been brought into play. It features a dimpled surface on the outer sides of the cylinder sleeves which offers more surface area for cooling water to run over. The water intakes have been doubled from the standard one on each side of the upper gear case with another two on the front of the 'bullet' of the gear case. It will be interesting to see how the latter performs around shallow structures as it will take the brunt of any collisions with such things as mud banks and other materials that might tend to clog the system.

To harness all of this power output, Yamaha have designed a new range of propellers called Saltwater Series XL.

On the technical side, the V8 has four valves per cylinder and the running of the unit is via the information fed to the Engine Control Module (ECM) from seven different sensors.

Variable camshaft timing advances and retards the angle of the intake camshaft to increase valve lift, duration and overlap in the low to mid ranges, for greater torque between 2000 to 3500rpm when planing large boats.

The incoming air runs through a labyrinth of passages that trap water and send it to a pair of drains in the lower cowl. The air then enters the 81mm intake controlled by the ECM to ensure the precise amount is going into the engine, taking into account atmospheric conditions and information coming from the sensors. Each cylinder has its own tuned intake track, which exits the gathering point near the front of the block, running along the sides and entering the aft end of the block at its respective cylinder.

The above-water exhaust outlet is a dual labyrinth system that greatly reduces noise.

These engines will be fitted to some fairly cluttered work platforms and production boats, the manufacturers of which could not have taken into account the ever increasing size of the engines of the future.

BIG HEAD
The big issue then is the size of the power head and the room it might not have when the engine leg is tilted up. Yamaha has the ability to change the upper tilt-stop level by computer via the Diagnostic System. That should alleviate engine cowls breaking on baitboards and the like.

If slow trolling or wanting to hold the boat into an oncoming current, the rpm range may be adjusted in 50rpm increments between 600 and 1000rpm.

Each cylinder hosts its own Ionic Combustion Sensor which monitors for incomplete combustion of fuel and which messages the ECM to adjust spark timing to alleviate this problem when detected.

Also on the horizon is a 300hp version of this engine for those that want the thrust but not the horsepower of the 350. Well, a day on the water aboard three boats fitted with these new additions was interesting.

V8 PERFORMANCE
A pair of the V8s were fitted to a 31-foot Grady-White, itself an innovative boat. The Yamahas provided plenty of power to push the 5200kg hull with eight adults aboard onto the plane. With both engines synchronised and running at 5900 rpm, the Grady-White was clipping along at 42.8kts with a fuel consumption of 250lt/h for both engines.

A single V8 was fitted to a Stabi-Craft 809SC Super Cab. At full throttle it realised a top speed of 43kts using 119.4lt/h at 5800rpm.

Another V8 was fitted to an 8m Commodore which is a hardtop fibreglass boat out of WA. At 5900 rpm it achieved 79kmh or around 42.6kts at 5900rpm.

The noise levels in the cockpit of all boats were very acceptable by today's four-stroke standard. Seated at the rear lounge in front of the twin rig on the Grady-White, conversation was easily had and voices were barely raised among the occupants at cruising speed.

We were half expecting the throb of a V8 from the exhaust but not so. With the leg up and the exhaust hub near the surface, there was a slight hint of a burble but nothing like you would get out of a V8 with twin exhausts on the highway. Amazing! The size of this V8 is bigger than many fitted to sports cars.

Those looking for a twin rig will like the digital remote control for the engines which is as smooth as silk.

Yamaha offer a two-year warranty which may be extended to four if all servicing is carried out by an approved Yamaha service technician.

Depending on the length of the shaft, you can expect to pay between $38,000 and $43,000 for the pleasure of owning one of these awesome outboard engines.