We shot some on-the-water video and let you know the moment the Suzuki DF350A twin propeller outboard engine was introduced, and now we’ve had time to dig deeper into the particulars of this powerhouse. Two details reveal the importance to Suzuki of the launch of its new DF350A outboard. First, the new motor has a pet name: Geki, which translates to “parting seas” and speaks to Suzuki’s intention to create a “force to match the power of nature and the sea.” There’s even a Geki kanji symbol Suzuki put on the media materials and a sticker. It’s not unusual for new engine products to get assigned an internal development name, but very unusual for that name to migrate to public-facing communication. The second eye-opener was the appearance at the Boca Raton media intro of Toshihiro Suzuki, president and CEO of Suzuki Motor Corporation, who flew in from Japan. I have never seen Mr. Suzuki at a marine-engine media launch. This was a big deal.
The new Suzuki DF350A is also a big deal, in more ways than one. The 4.4-liter V6 is the largest-displacement four-stroke outboard ever produced. In design, the new powerhead is very similar to the 4.0-liter V6 Suzuki created for its DF300/250 models. Both engines splay the cylinders at a narrow, 55-degree angle that mitigates the width of the double over-head camshaft heads. At 727 pounds (25-inch model) the DF350A weighs 88 pounds more than the Suzuki DF300. Much of that weight gain can be attributed to the new motor’s most-obvious new feature, its twin contra-rotating propellers.
Moving today’s heavy, outboard-powered offshore boats requires plenty of power and propeller blade area. Just as wide tires help a racing car connect to the pavement, more blade area helps to better transfer outboard power to the water, especially as the motor is straining to push the hull on plane. According to Suzuki the twin 15.25-inch diameter props of the DF350A offer 80 percent more total blade area than the single 16-inch prop it usually fits to its DF300AP model. Front and rear props are the same diameter and pitch. The twin props push the boat forward and – this is almost more important – provide extra lift at the transom to leverage the bow down as the boat comes on plane. The props are driven by concentric prop shafts and a pinion gear set in the lower gearcase, and both props function in forward and reverse. This highlights another advantage of the twin-prop design. The torque load is shared by the two driven gears, which can then be smaller than a single gear designed to handle 350 HP. This also allows Suzuki to keep the gearcase profile slimmer, and when combined with a new, more-efficient shape, counters the added drag of the second prop.
What about shifting? Forward and reverse are selected in the upper gearcase with dog clutches and gears on the drive shaft. The shift rod is located on the rear of the case, rather than the front, and is controlled by an actuator up near the powerhead. To keep the lower pinion and the upper drive shaft gears lubricated, the DF350A holds three quarts of gear lube, compared to about a quart for the Suzuki DF300AP model. Like other Suzuki outboards, the DF350A also has a two-stage drive shaft. There’s 1.25:1 gear reduction between the engine crankshaft and the driveshaft, combined with 1.83:1 reduction in the gearcase for a final drive ratio of 2.29:1, again achieved with more compact lower gears than would be possible with single reduction.
Other twin-prop benefits include better bite on the water in high-speed turns, better control at no-wake speeds and in reverse (especially on a single-engine boat), and a smoother steering feel;. And, of course, there’s no need to rig counter-rotating outboards on multi-engine boats. Mechanically the Suzuki twin-prop drive is similar to the Volvo Penta DuoProp and MerCruiser Bravo III sterndrives, which use concentric shafts and a pinion in the lower unit, with forward/reverse shifting accomplished on the drive shaft. Yamaha offers its TRP twin-prop gearcase as an accessory (TRP was initially offered with a 150 two-stroke powerhead as a complete engine in the late 1990s) but it’s a short gearcase designed for bass boats and some shallow-water skiffs.
I sent most of my demo time aboard a Dusky 33 Open fisherman, a 33-foot center console with a 10-foot 10-inch beam and a dry weight of 6,700 pounds. Rigged with a pair of Suzuki DF350A motors with 27-pitch props, the boat had a top speed of about 60 MPH and would run from zero to 30 in 6.5 seconds. Planing performance was simply outstanding. The boat powered forward with minimal bowrise and I really could feel the motors lifting the transom when I mashed the throttles. There’s so much lift, in fact, that on one occasion when I forgot to trim the motors back down before testing for hole-shot, the boat still planed effortlessly with no bowrise. Suzuki Product Planning Manager David Greenwood, who has been testing the DF350A for almost two years on a variety of boats, told me he’d made the same observation more than once. “You can almost just leave the motors trimmed for cruising speed,” said Greenwood, who added that the motors like to be mounted high on the transom, usually on the bracket’s top holes, which further reduces drag.
The Suzuki DF350A weighs 59 pounds more than the Mercury Verado 350, a supercharged 2.6-liter in-line six. The other competitor in this class is the 765-pound 5.3-liter V8 Yamaha F350C.
Each brand takes a different approach to produce the prodigious thrust required to push large, heavy boats, from big offshore fishing boats to the largest pontoons. Mercury boosts the performance of its smaller-displacement powerhead with a supercharger that delivers a very effective kick in the transom. Yamaha gets there with sheer displacement and a huge prop; the F350C is more locomotive than sports car.
To squeeze 350 HP from 4.4 liters (80 HP per liter) Suzuki started with a new cowl design that features dual intake louvers and passages lined with rows of small vanes or fins designed to convert water vapor to heavier particles that are then drained away. The result, according to Suzuki, is a flow of dry air to the engine that is never more than 10 degrees warmer than ambient. Cooler air makes more power, of course. Intake and exhaust ports are re-shaped, and the engine features dual 10-hole fuel injectors for each cylinder that deliver a fine mist of highly atomized fuel and eliminate fuel puddling before the intake valves. The range of the variable intake camshaft timing is increased to 30 degrees from 20 degrees, and the engine is fitted with shot-peened slipper pistons that are very strong and very light weight. WOT operating range is 5700-6300 RPM. The compression ratio is a very high 12:1 and to extract maximum power the motor should get 91 octane fuel.
The DF350A is also equipped with the full suite of features Suzuki has introduced on previous V6 outboards, including Lean Burn Control that leans out the fuel/air ratio for better economy at cruising speed, Suzuki Precision Control drive-by-wire throttle and shift, troll mode that permits engine speed adjustment in 50 rpm increments from idle to 1200 RPM, a self-adjusting timing chain that runs in an oil bath, a fuel cooler, and a dual-circuit charging system. Alternator output is 54 amps with 40 amps available at 1000 RPM. Finally, there’s an improved attenuator that tunes out intake noise; on our Dusky test boat I could not hear the Suzuki outboards at idle from the helm. Which is why I turned the key when they were already running… oops!
That’s a lot of bells and whistles and they all come at a price. Suzuki will release official pricing later this summer but expects the DF350A to carry an MSRP a little more than $30,000. Boat builders will of course determine the price of factory-rigged motors. Good geki never comes cheap.
For more information, visit Suzuki Marine.