By Thomas P.

(June 9th, 2017)
Once again, Suzuki takes the lead in innovative technologies by announcing the new twin-prop DF 350 A outboard engine, a real revolution in the outboard engines’ history.

SUZUKI  Duoprop 350 hp

SUZUKI engineers never stop surprising us, by setting new rules on the market and a new course for the future of outboard engines.

Adding a second, contra-rotating propeller to the propshaft improves the performance and handling of each boat by providing:

  • greater acceleration
  • much better bite on the water
  • shorter time to plane and lower-rpm planning ability
  • significant reduction of slip percentage resulting in higher cruising speed and better fuel economy
  • elimination of the steering torque and less ventilation in tight turns
  • better control in reverse
  • improved performance on heavily loaded boats

Additionally, the second propeller decreases the torque per propeller and thus reduces the need for a large gear diameter, allowing a smaller and more hydrodynamic gear case. With the additional three blades it is possible to produce a greater thrust with smaller diameter propellers due to the increase in the total blade surface. Thus, propellers recommended are of smaller diameter despite the large gear ratio:
3 x 15 ½ X 19.5" - 31.5".

Suzuki's new, powerful six-cylinder 350hp outboard engine began to be designed on a blank sheet of paper and has been developing for more than three years, representing a milestone in both engineering and design.

With a particularly low weight for its 4.390 cc (the XL one reaches 330kg and the XXL 339 without engine’s oil and propellers) it’s combined with high revs per minute (5700-6300rpm) and a final gear ratio of 2.29: 1, making it the only 350hp engine with such a large (numerical) gear ratio.

Till now, all outboards manufacturers were used to reducing (numerically) the gear ratios as they were increasing the horsepower. It is the first time we see the gear ratio increased in parallel with the horsepower. Thus, while the DF 300hp had a gear ratio of 2.08: 1 and we would expect a 1.85: 1 one in the new DF 350hp, the Suzuki’s engineers applied a larger gear ratio due to the high torque requirements of the two propellers.

SUZUKI  Duoprop 350 hp

The twin propellers, the high horsepower and the large gear ratio in this horsepower are an explosive combination of torque and thrust, making the DF 350 A the most powerful engine on the market, in its class.
It is certain that the new engine will be ideally suited to heavy boats, to 10m light boats which till now required inboard engines or dual outboards so as to move dignified, and generally to large pleasure boats which have the need of great torque.

The innovative and high-tech features of the new Suzuki DF 350A include:

Suzuki Dual Prop System

While contra-rotating propellers are not a new technology, they have never been successfully used on outboard motors until now. The DF350A’s dual propellers provide three key benefits, compact size, increased stability and greater “traction.”

By distributing the power of the engine over six blades, instead of just three, the size of the gears and gearcase could be kept to a minimum, which in turn allowed for the design of sleeker, more hydrodynamic gearcase. Suzuki engineers spent many hours in computer simulation and on the water, knowing that reducing drag underwater would be essential to improving overall boat speed and performance.

SUZUKI  Duoprop 350 hp

Contra-rotating propellers also provide added surface area, for more stability and increased «traction» or grip underwater. (Think of the wide slicks on a drag racer as compared to typical tires.) This results in exceptional acceleration, or hole-shot, truer directional propulsion (eliminating steering torque), better than expected top speeds and incredible reverse thrust. Importantly, these benefits are apparent even on heavier boats with full loads of fuel, gear and people.

12.0:1 Compression ratio

Suzuki engineers achieved 350 horsepower while still designing a compact, lightweight powerhead. The robust engine displacement of 4.4 liters is matched by a high-performance 12.0:1 compression ratio, the highest ever for a production outboard engine.
A unique combination of cool air intake, dual fuel injectors and a strengthening of the pistons has virtually eliminated engine knock, a typical by-product of high compression engines.

SUZUKI  Duoprop 350 hp

Dual Injectors

Two, smaller fuel injectors allow for precise injection of fuel to the center of the combustion chamber, which avoids off-center combustion – a major cause of knocking.

In addition, because 100% of the fuel is injected into the cylinder at once, a degree of cooling is also obtained, providing up to 3% additional power without causing knocking.

SUZUKI  Duoprop 350 hp

Suzuki Dual Louver System, Direct Air Intake

Suzuki engineers have designed an air intake system that allows the engine to draw in ample fresh air, while separating out water, spray and moisture. Dual louvers under the hood trap larger water droplets and then moisture as it enters the engine cowling, resulting in zero water intake during testing.
In addition, intake air temperatures are, on average, 10º cooler than ambient, providing the combustion chamber with cooler, denser air for a more powerful cycle.

SUZUKI  Duoprop 350 hp

Advanced Piston Technology

To achieve 350 horsepower, the surface of the piston needs to withstand added forces. In order to assure both performance and long life, Suzuki engineers switched from a standard heat treatment to «shot peening». Shot peening, a more expensive process, creates fine dimples in the face of the piston that evenly distribute the pressure created during combustion. In addition, the connecting rods and hardware have been strengthened to handle the added loads.

SUZUKI  Duoprop 350 hp

In addition to the above high-tech features, the new DF 350 A includes all the well-known and remarkably innovative features of Suzuki’s previous models, such as:

  • Suzuki Precision Control
  • Suzuki’s offset driveshaft engine layout, which allows for a more compact outboard and two-stage gear reduction
  • Suzuki’s Lean Burn Control Technology, for improved fuel economy throughout the entire rpm range, and especially at cruising speed and like all Suzuki 4-stroke outboards, the DF350A is extraordinarily quiet at idle.

It’s worth noting that the technology of the DF 350A’s contra-rotating propeller eliminates the need of combination standard and counter-rotating engines when mounting multiple outboards on the transom.

As you can see, the development of this new outboard has been driven by Suzuki’s belief that it is important to provide the market with more than just horsepower. While power and speed are critical factors, the added dimensions of efficiency, reliability and stability make the DF350A the Ultimate 4-Stroke Outboard.

 

The DF350A will be manufactured in Suzuki’s Toyokawa plant in Japan and will be available in the US in July, 2017 and worldwide later in the summer.

For more information on Suzuki’s new DF350A or their full line of 4-stroke outboard motors from 2.5 to 350 horsepower, please visit www.globalsuzuki.com