Suzuki DF350A | Boating Magazine

Suzuki DF350A

Suzuki’s new DF350A outboard sets a high standard.

Suzuki DF350A

In comparing test notes on a Dusky 33 Open Fisherman, twin Suzuki 350s boosted top speed by 7.1 mph over twin Suzuki 300 outboards.

Suzuki

More than three years ago, a Suzuki ­engineering and design team in Japan set out to create a 350 hp outboard that would break new ground in features, performance and efficiency. The team had a watchword for this project — Geki, ­Japanese for “parting the water.”

This became a driving force behind an endeavor to rethink how a big, powerful outboard should function, and then to strive to bring it to life. Based on my time running the engine in several configurations and getting the tech scoop from ­Suzuki’s engineering team, I believe that all that creativity, risk and toil paid off.

The new DF350A offers a number of innovations, including a lower unit unlike that of any other outboard today. A pair of contra-rotating three-blade propellers deliver power to the water. Of course, the MerCruiser ­Bravo Three and Volvo Penta DuoProp sterndrives, as well as the now-discontinued VMax TRP 150 outboard from ­Yamaha, also feature twin props, boasting benefits we have come to appreciate: strong hole shot, minimal prop torque, better bite in turns, as well as great handling in forward or reverse.

The DF350A offers the same advantages, plus a few more. ­Contra-rotating twin props allow for distribution of torque across two smaller gears. This keeps the gear case as small as possible to increase efficiency and boost top speed yet still ­accommodate the torque.

To maintain a smaller lower unit, ­Suzuki engineers moved the shifting system above the gear case. They also refined the hydrodynamics using computer simulations to create a super-slippery shape and feed clean water to the props. The new design repositions the ­primary cooling water pickup to the front of the bullet, with a secondary pickup on the ­underside, just forward of the skeg.

Suzuki DF350A

Contra-rotating props help keep the gear case small and hydrodynamic.

Suzuki

Yamaha boosts outboard horsepower to the 350 range by utilizing greater ­displacement, as with its 5.3-liter V-8 F350 outboard. Mercury boosts the pressure of the intake system with its supercharged 350 Verado. Suzuki took a different course.

At 4.4 liters, the DF350A’s displacement is indeed slightly higher than Suzuki’s DF300AP’s 4 liters. Yet its 12-to-1 compression ratio — the highest so far for an outboard — is what makes the difference.

While higher compression ratio results in greater horsepower per cubic inch, it also holds the potential to induce ­detonation (aka “knock”) that can hurt performance and damage an engine.

A key to preventing knock is to keep the intake as cool as possible. To do this, the DF350A features an intake in the hood that feeds air directly to the engine. A series of small louvers wick away moisture as air accelerates through the slots, so the air is dry and no more than 10 degrees above the ambient temperature.

Suzuki also engineered the DF350A with two fuel injectors per cylinder. These not only simultaneously deliver a finely atomized charge of fuel but also cool the intake air more effectively than a single injector.

A number of features carry over from the DF300A, including electronic throttle and shift for smoother control, Lean Burn to maximize fuel efficiency, an offset drive shaft that shifts the center of gravity forward, two-gear reduction to help keep the gear case compact, variable valve timing for optimal low- and midspeed power and efficiency, and a self-adjusting timing chain that requires no maintenance.

Like many other Suzuki outboards, these engines are exceedingly ­quiet, ­especially at idle. But even underway, the emanated noise is relatively low. On our runs, the DF350A vaulted out of the hole with head-snapping velocity and held its bite in tight turns with remarkable tenacity.

This 350 will find application on a wide range of boats, but Suzuki is focusing much of its attention on the growing number of big center consoles sporting triple and quadruple outboards. A popular horsepower in this category, only two other brands — Mercury and Yamaha — ­currently offer 350 models.

There’s another advantage here to having contra-rotating props: It eliminates the need to mix right- and left-hand rotating motors in multiple-outboard installations. With 27-inch centers, the DF350A fits the same transom bolt pattern as the DF300A, making for a relatively simple retrofit, be it single or multiple outboards.

XL (25-inch shaft) and XXL (30-inch shaft) models are available, weighing 727 and 747 pounds, respectively. These are about 35 pounds lighter than the Yamaha F350 but around 60 pounds heavier than the Mercury 350 Verado. Suzuki offers the DF350A in two colors: pearl nebular black and cool white. Pricing was unavailable at press time.

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