Suzuki DF350A

Compression Ratio

Our solution to developing 80 horsepower per liter in a V6 350 horsepower engine was to increase the compression ratio to 12.0:1, the highest compression ratio ever for a production outboard engine. In order to make this work without knocking (a typical problem at this ratio), we developed systems to mix cooler air with well-atomized fuel to provide optimal conditions for complete, and controlled combustion.

Direct Intake System and Dual Louver System

Increased intake flow converts water vapor to particles. Designing blades capture and deflect those particles away from the intake flow. The dual louver system removes the spray from the boat, captures and drains the remaining mist resulting in the intake air temperature being free of moisture and no higher than 10 degrees above ambient.

Dual Injectors

Injecting fuel does two things, it atomizes the fuel and, it cools the cylinder to minimize knock. To achieve the power we wanted, we needed to inject 100% of the fuel into the cylinder all at once, at a precise time, and at a precise angle to both cool the cylinder and to allow combustion to take place in the center of the combustion chamber. The new Dual Injector System using two smaller injectors provided the required precision as well as improved atomization , increasing output by 3% without knocking.

Contra-Rotating Propeller

The contra-rotating propeller provides more “grip” underwater, and because contra-rotating props distribute the engine torque evenly over two propellers, the torque per propeller decreases and gear diameter can be reduced. This leads to the design of a smaller, more hydrodynamic gear case.

Propeller Blade Design

A new three-blade front/three- blade back propeller set-up was developed and provided improved performance on the water. This new set-up provided not only the highest recorded speeds for the DF350A, but also delivered incredible acceleration, even under heavy load and at high rotation speeds.

Dual Water Intakes

On the DF350A, the best results were achieved when the main intake was positioned at the front of the gear case, with the secondary intake located just above the skeg. This was out ultimate solution to arranging the main and sub intakes as far apart from each other as possible, and designing them to ensure a reliable amount of cooling, especially at high speeds.

Stronger Reverse Thrust Design

The gear material was changed and heat treatment was added to endure the added thrust and inertial mass from the reverse thrust, which was stronger on a contra-rotating propeller. In addition, the reverse gear was moved above the cavitation plate and the position of the lower engine mounts was modified from parallel to V-shape to fit the reverse gear above the cavitation plate.

Better Steering in All Directions

Normally, when using multiple outboards a combination of standard and counter-rotating engines are mounted. The Suzuki Selective Rotation is available on our AP series outboards, eliminates the need for different models, as any model can be easily programmed to run in either direction. The DF350A’s contra-rotating propeller technology takes this process one step further by eliminating steering torque and maximizing true and straight propulsion forces.