It’s no secret that there is a growing demand for more powerful outboard motors.

These new outboards have, in turn, fueled a move to newer, larger boat designs that previously may have been powered by stern drive or inboard power.

So, as more powerful outboards are introduced, the boats get bigger and as the boats get bigger, outboards are getting more muscular. Suzuki embarked on a major engineering expedition to build the Ultimate 4-Stroke outboard.

Is The Sky The Limit?

Making more horsepower is no mystery. Increasing displacement, or the use of a turbocharger or supercharger, makes more horsepower. However, larger displacement engines typically burn more fuel, adding weight creates a wide range of problems for boats, and more complex mechanical components create reliability concerns.

On top of all this, boat speed is ultimately limited by hull design, the hydrodynamics of the lower unit and propellers, and how the outboards are mounted.

In developing our new DF350A, we started with a blank sheet of paper, and considered all these factors in our design and engineering.

First, we looked at the traditional single propeller design. A single propeller creates forward thrust, to be sure, but also produces a significant amount of rotational energy as a byproduct. Was there a way we could convert this wasted energy into productive power and improve propeller efficiency?

Secondly, the leading edge of the gear case disrupts the flow of water over the propeller. More power and torque require stronger, larger gears to transfer power from the driveshaft to the propeller shaft.

This typically results in a larger gear case – and consequently, more disruption of the flow of water to the propeller. Could we design a lower unit that could house stronger gears and yet minimize the disruption of the flow of water to the propellers?

Suzuki engineers labored mightily through years of computer simulations, trial and error, and on-water testing, to significantly improve the way an outboard converts engine power into underwater thrust.

They have succeeded in this quest – and the result is a revolution in innovation.

We call it Parting Seas (Geki kanji symbol..)


A Force to Match the Power of Nature and the Sea
Representing Suzuki’s Identity and Heritage
A Symbol of Our Passion and Commitment
to the Ultimate in Marine Innovation




Katsuhiro FUKUDA

Chief Engineer

Since the development of the world’s first 300 horsepower 4-stroke outboard in 2006, DF300 has been brought up and trained by our customers to evolve into DF300AP, which is equipped with the Suzuki Lean Burn Control and Suzuki Selective Rotation systems.
DF300 has been praised by customers for the reliability and durability, but meanwhile, there were many customers who demanded more power. 

In the development of DF350A, the scene I imagined first is our customers using DF300AP and shouting “Wow!”
Suzuki’s V6 engines have a narrow 55-degree bank angle, so the minimum interval is 27 inches when rigging two outboards.
“Can you mount this engine on my boat?” “No. The engine got bigger as the horsepower increased. So, please buy a new boat.” Such a response will let our fans down.

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The concept is a 350 horsepower engine that DF300AP users can rig easily on their boat.
Then, V6 with a narrow 55-degree bank angle becomes our unavoidable condition. We planned to keep the bore pitch 108 mm to be the same as our reliable and durable DF300AP. This was the starting point of development.
There were many challenges to overcome.

First priority is power output. For that purpose, it is common to increase the displacement, but it decreases fuel economy and makes it difficult to realize the bore pitch of 108 mm. After repeated development test, we found that with displacement of up to 4.4 L, we can keep the engine as small as DF300AP.

The layout was made possible, but to output 350 horsepower, the engine must produce 80 horsepower per liter. DF300AP has already achieved 75 horsepower per liter, but 80 horsepower per liter was uncharted territory for us. To achieve this, in any case, we must improve the combustion inside cylinders.

Mr. Saiga lowered the intake temperature by means of a direct intake system with a dual louver to fulfill the requirement for more power. Mr. Achiwa optimized the shape of the combustion chamber to achieve the compression ratio of 12.0 with an outboard for the first time.
I’m sure you will be excited at the sound of Suzuki from the dual louver.

What about performance? Ordinary small displacement engines take longer time to start planing than large displacement engines. They also cannot accelerate sharply on demand.
Mr. Sugiyama solved this problem by optimizing the shape of the gear case and using a contra-rotating propeller. You shall experience powerful acceleration you wouldn’t expect from a small displacement engines.

Meanwhile, we achieved the fuel economy comparable to DF300AP thanks to the small displacement and lean burn control.
Although using the same 55-degree bank, DF350A reflects 10 years of evolution in every detail.
Even a single head bolt is newly designed.
Suzuki outboards have been brought up by customers and continue to evolve at this time as well.

We have kept you waiting for a very long time.

We’re proud to say it’s finally here. Please experience Suzuki’s flagship model, which is worthy of being called the ultimate 4-stroke outboard.

Atsushi OHTANI

 Product Designer

Innovative, aggressive, and sporty design.
Dynamic design that you can recognize as a Suzuki outboard at a glance. Quality design that is suitable for the flagship model and gives you the joy of possession. These were the most important factors in developing DF350A.

As for the details of its design, we expressed the characteristics of Suzuki outboards with the dynamic silhouette of a slant shape with an obliquely scraped forehead and raised rear end. And as a characteristic feature, we designed the side openings to show the vertical fins of Suzuki Dual Louver System, our original air-water separator.

Taking each character line and part parting line as an organic and emotional character, we have succeeded in expressing the elegance with these long-stroke lines flowing beautifully and three-dimensionally. We also created a joyful atmosphere with two-tone color painting of nebular black (or white) and silver.

The overall shape is designed to make users imagine speed even with the outboard alone while considering the sense of harmony with the boat. DF350A is designed with the goal of being chosen also for its beauty, featuring outstanding design beyond that of a mere power unit.

We have succeeded in achieving both the ultimate compactness and superior design without unnecessarily increasing the volume.

Tetsushi Achiwa

Design Group, in charge of Engine

At the first trial production of DF350A after obtaining some prospects through repeated preliminary tests using DF300AP as the base, the output performance was far from that we had expected.

As a result of aiming at the high compression ratio of 12.0, knocking inevitably occurred, and therefore we could not achieve the ideal high output.

To achieve 350 horsepower with a small displacement, the compression ratio of 12.0 is indispensable, and also there was a concept of a compact engine. So, we could not change the layout largely.

Then, we returned to the starting point and thought of reconsidering the design of the combustion chamber.

We repeated CAE in order to increase the amount of air agitated in the chamber while increasing the air flow for combustion, and finally reached the current shape in which the piston top protrudes to the head side.

Since the shape was unlike any Suzuki had experienced before, we had no experience about the manufacturing and quality control methods, and therefore we faced disapproval from the relevant parties. So, we explained over and over and eventually convinced them that the shape was necessary for achieving the “ultimate” performance, and had them devise the manufacturing process so that it can be adopted to mass production.

Even if the propulsion efficiency gets better with a contra-rotating propeller, the target performance cannot be achieved if the engine output is low.

Moreover, unless the engine outputs the target output, we cannot even start the evaluation tests of propulsion functions and operability using actual outboards.

We made improvements day by day while feeling heavy pressure on engine improvement from the designers of other parts as well as the persons in charge of experiment.

This high performance engine is the result of squeezing wisdom to meet the expectations from the surroundings.

Shuichi Sugiyama

Design Group, in charge of Lower Unit

“Form follows function.”
This is one of my favorite words.
The lower unit of the DF350A is a realization of these words. A gentle, elegant periphery of the shell, an outstandingly tough and strong material surface, and a contra-rotating propeller that helps them harmonize with each other.
Each of them has its own function and gives it shape.

The DF350A is our next step for specification without counter-rotation after the Suzuki Selective Rotation, which was developed in 2011. It was a very valuable experience for lower unit designers to be able to challenge the contra-rotating propeller specification as the next step following Suzuki Selective Rotation. Development of a new technology is always a series of failures, and we cannot overcome failures with only conventional design methods.
Why does new technology fail? How can we adopt new technology? We noticed one thing while repeating failures.
It was that we cannot adopt new technology without complete understanding of conventional technology.
And to have complete understanding of conventional technology, we must keep asking ourselves, “How should it really be?”.
The “form” mentioned at the beginning is the result of repeatedly asking “How should it really be?” for each function.
The DF350A is packed with new technologies in addition to conventional technologies that have come back to join.

Who will be the customers feeling the DF350A?
As an engineer, I cannot help but be excited.

Jiro Saiga

Design Group, in charge of Cowling

We want more horsepower. To increase horsepower with the cover, it is necessary to supply the outside air to the engine while maintaining the temperature. For that purpose, we adopted the direct intake system.
We knew how one of our competitors had been evaluated after adopting a direct intake system. We were prepared for difficulty.
We must never allow a single drop of water into the engine. In order to achieve absolute water separation, we adopted the dual louver system consisting of inner and outer louvers arranged parallel to each other with dog-leg shaped louver blades.
The outer louver removes water drops sprayed by the hull, and the inner louver removes the finer mist. The dog-leg shaped louver blades increase the intake flow rate as much as possible to hit against blades the water drops and mist contained in the intake air and thoroughly remove them.

The shape of the outer louver, which has never existed before, has a strong influence on the appearance of DF350A.
In order to satisfy the horsepower and absolute water separation while making the appearance of DF350A more impressive, we modified the design model over and over again. By making and examining various prototypes of different angles and intervals of the blades, we successfully achieved a satisfactory shape. In order to ensure stable louver performance, we had decided to make each louver with a single part. We created a digital 3D model considering the requirements for manufacturing.

We’ve never seen such a part. Can we really mass-produce it?
We had a meeting with a molder and mold manufacturer feeling anxious. Sure enough, they asked us, “Please show me the reference parts”. Our answer was, “We have never seen one.” The mold manufacturer got serious. We covered everything from designing the actual part to designing the mold. We are satisfied that we were able to design a truly genuine piece.


IBEX Innovation Awards are the best awards in the marine technology, which are given to those new products in the marine industry that demonstrate distinctive technological innovations and deliver outstanding consumer benefits.

The following features of the DF350A were valued for the receipt of the award:
– The largest V6 engine displacement, at 4.4 liters
– Suzuki Dual Prop System (for exceptional grip and acceleration)
– Direct Air Intake & Dual Injector (for achieving high compression ratio and efficient combustion)
– Dual Louver System (for efficiently separating air and water)
– Low Fuel Consumption

This is the ninth Innovation Award won by Suzuki outboards, which accredits our sophisticated technology.
Eight of these awards have been for four-stroke outboard motors, which is the largest number of awards in the engine category of this industry.

This outboard motor is worthy of being called a flagship. It has a unified and sophisticated form, enwrapped in organic curves from the air intake to the propeller.
The color and logo give a serene feel worthy of a flagship model that will grab attention.

As for performance, stability is improved with the implementation of the rare dual propeller system.

In terms of both design and engineering, this product represents a dynamic jump for Suzuki’s outboard motors.

About Good Design Award

The Good Design Award is a comprehensive design-promotion system that picks good design out of a variety of unfolding phenomena, and aims to enrich our lives, industries, and society as a whole by highlighting and celebrating these works. It is hosted by the Japan Institute for Design Promotion, a public interest incorporated foundation.