Suzuki unveils new 350-hp outboard

Posted on Written by Eric Colby
Twin Suzuki 350-hp DF350A engines are shown on an Avalon pontoon boat.

Twin Suzuki 350-hp DF350A engines are shown on an Avalon pontoon boat.

Suzuki today introduced its largest outboard motor to date at the Boca Raton Resort and Spa in Florida.

The DF350A is a 350-hp fuel-injected V-6 with innovative features that include twin counter-rotating stainless-steel propellers. By spreading the load over those propellers, Suzuki achieved two goals. The second propeller improved the motor’s grip and overall performance.

The torque per propeller was also decreased, which allowed for smaller-diameter gears. That, in turn, resulted in the design of a smaller, more hydrodynamic gear case.

Previously the biggest outboard Suzuki made was a 300-hp 4.0-liter (244.1-cubic inch) V-6. The new model is a 4.4-liter (268.4-cid) 55-degree V-6 with a maximum operating range of 5,700 rpm to 6,300 rpm and a bore and stroke of 3.86 inches (98mm) x 3.82 inches (97mm).

This is the biggest displacement V-6 on the market, and Suzuki did not want to lose too much ground in the weight department. Weighing in at 727 pounds for the 25-inch shaft length and 747 pounds for the 30-inch model, the DF350A is about 87 pounds heavier than the DF300. All of the available propellers for the motor are 15½ inches in diameter and pitch ranges from 19½ inches to 31½ inches.

The DF350A features twin counter-rotating stainless-steel propellers and other innovations.

The DF350A features twin counter-rotating stainless-steel propellers and other innovations.

Suzuki’s goal with the DF350A was to develop 80 hp per liter, but a block with too much displacement would have meant more weight and the designers did not want to use a supercharger or turbocharger to boost the power.

The solution was to increase the compression ratio to 12.0:1, the highest of any outboard motor. A high-compression ratio can often make an engine prone to knocking, so Suzuki developed new fuel-injection and air-intake systems to work with the high-compression ratio.

A key to preventing knocking is keeping the air-fuel mixture cool and finely atomized when it’s injected into the cylinder. To help accomplish this, Suzuki engineers developed a dual louver system on the DF350A’s cowling, designing blades with a dogleg design to capture and deflect water particles away from the air in the intake flow. The intake air is free of moisture and never gets hotter than 10 degrees above ambient temperature.

Using two props made sense, so for fuel delivery Suzuki used a dual-injector system with two smaller injectors per cylinder. They provide more precise atomization of the fuel at the most efficient angle before it’s injected into the combustion chamber. Higher compression means more violent combustion, so the pistons were redesigned with shot-peened surfaces and beefed-up connecting rods and bearings.

Some Suzuki technology that has been proven on previous models is still in use on the DF350A. Suzuki Selective Rotation lets any model be programmed to rotate in either direction. The manufacturer’s two-stage gear reduction results in a large reduction-gear ratio (2.29:1) that gives Suzuki the ability to simultaneously prop the boat for quick acceleration and a higher top end.

The offset driveshaft design places the crankshaft in front of the driveshaft, moving the engine’s center of gravity forward. This results in better weight distribution and balance, more directional stability and less vibration.

The DF350A runs on 90-octane fuel, the same as its competition. The DF350A can still fit on 27-inch centers, and it takes conventional hydraulic steering, which makes the motor a good candidate for repower projects.

Suzuki offers it with a joystick system from SeaStar Solutions and can add SeaStation position keeping. Suzuki pairs the DF350A with its C10 helm display, and it can cross-reference with virtually any instrument that is NMEA 2000-compliant. Retail price for the DF350AX is $31,565 for the 25-inch version in black. The motor is also available in white.

Suzuki expects to have a limited amount of the new motors available to manufacturers this summer so they can have them for late-season dealer meetings. The DF350A should be at dealerships by the end of the 2017 season.

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