The engine builder launches 350hp outboard with dual propellers
Suzuki’s new 350hp outboard goes under the microscope plus, Lowrance HDS-16 Carbon; Dinghy Rings; Yamaha F2.5 outboard; Gill 7014 Blackwater Level Sensor; Esthec luminous decking
Suzuki has unveiled its most powerful outboard ever – a 350hp V6 4-stroke with some very unique features. Only two other mainstream engine manufacturers, Mercury and Yamaha, can match this power output and neither of them can offer the Suzuki’s dual-prop setup.
In fact, everything about this new engine has been designed to offer a different boating experience to its key rivals. That starts with the way it has gone about creating the extra grunt; rather than relying on a supercharger (Mercury) or a larger-capacity engine block (Yamaha), it has taken the altogether trickier route of squeezing more power out of its existing 4.4-litre naturally aspirated V6. The payoff is a light, compact engine with plenty of power, rapid throttle response and low fuel consumption.
The most significant enhancement is an unusually high compression ratio of 12.0:1 – the highest ever for a production outboard engine. This enables it to develop more power from the same size block without the need for forced induction from either a mechanically driven supercharger or an exhaust driven turbocharger, both of which add weight, sap power and increase fuel consumption. The difficulty with high compression ratios is ensuring the engine still runs smoothly and reliably without the engine knock that often afflicts this type of highly tuned motor. Suzuki claims to have resolved this through a combination of cool air intake, twin fuel injectors per cylinder and a special hardening and finishing process for the pistons and conrods.
One of the key innovations is a new dual-louvre system that feeds air into the cylinders. These specially shaped air intakes, comprising two rows of fin-like louvres, not only filter out every last drop of water and moisture before it enters the combustion chamber but also helps to cool the air as it passes. Suzuki claims the average intake air temperatures are 10° cooler than ambient, supplying the combustion chamber with cooler, denser air for a more powerful combustion cycle. In effect, this acts as a mild form of forced air induction.
The use of two fuel injectors per cylinder also helps to reduce knocking by ensuring a greater density of atomised fuel is injected into the centre of the combustion chamber rather than around the edges, as is the case with the cone-shaped spray from a single injector. This reduces the amount of off-centre combustion, one of the causes of knocking. Because the same amount of fuel can be injected faster, it also aids cooling, delivering an additional 3% power boost.
The surface of the pistons have been treated with a shot-peening process that leaves microscopic dimples on the piston face. These help distribute the high pressures created during combustion more evenly for reduced wear and a more consistent power stroke. The connecting rods and other moving parts have also been strengthened to cope with the increased loads.
TWO PROPS BETTER THAN ONE
Putting this much power into the water is always going to be a challenge from the point of view of both grip and mechanical strength. A single propeller typically uses three big blades to transmit power into the water, while the gears need to be strong enough to withstand the torque of the engine as the blades come up to speed. This in turn requires a larger gearcase which generates increased drag through the water. Suzuki’s answer is to adopt twin contra-rotating propellers that use six smaller blades to give better acceleration while simultaneously reducing the loading and size of the gears. This has allowed it to design a sleeker leg without the torque steer associated with a powerful single engine spinning a big prop in one direction only. It claims this is particularly noticeable on larger boats carrying heavy loads of fuel and people.
Last but not least, the new engine tips the scales at a relatively modest 330kg (midway between the 346kg Yamaha F350 and the 303kg Mercury Verado 350), while the slender design of its narrow-angle V6 engine makes it easier to fit multiple installations on transoms with limited space. Suzuki’s usual lean burn technology and electronic throttle control should ensure impressive fuel economy and easy handling for such a powerful unit, although no comparisons with rivals are currently available.
The new engine will be launched at the Southampton Boat Show in September with the first deliveries expected in December. Pricing will be announced at the show.
KEEPING A COOL HEAD
The slender design of the cowling is well suited for multiple engine applications
MY TAKE I’m intrigued to see how well this engine works. I like the fact that it doesn’t rely on forced induction to generate more power, but will it match the low-rev torque of the Yamaha and Mercury? Hugo
NAVIGATION Mel Bartlett
Nick Burnham PRODUCTS