Suzuki is renowned for being at the forefront of four stroke technology and creating outboard motors that boast a variety of innovative features. Their latest generation of outboards are no different — not only are they lightweight, compact and powerful but they deliver class-leading fuel efficiency, courtesy of Suzuki’s Lean Burn Control System.

With the rising cost of fuel becoming an increasingly important factor for customers deciding what outboard to buy, Suzuki’s engineers set out to develop a system that enabled their outboards to get even more out of every drop of fuel.

Suzuki's new Lean Burn DF300 - Photo Credit Suzuki Marine Europe

The project team that took on this task was headed up by Chief R&D Engineer Hitoshi Matsumura and involved a group of Suzuki’s most talented engineers who looked at every single aspect of outboard operation, from electronics through to engine and body design.

Based at Suzuki’s Research and Development Centre in Hamamatsu, this project became the focus for Suzuki’s marine engineers and after months of development and hundreds of hours testing the new outboards on a variety of boats to achieve optimum results, the new Lean Burn Control System was ready to bring to market.

Mr Matsumura said, “Our brief was to create an intelligent fuel management system to make our outboard motors even more fuel-efficient and allow the end users to spend more time out on the water and less time at the fuel dock.”

He continued, “The new system needed to be compatible with existing technologies to enable us to roll it out to current models as we have done with the new Lean Burn DF300. However, the Lean Burn project was also combined with re-designing each and every component part for new generation models such as the new DF60 to make them as lightweight and mechanically efficient as possible.”

First introduced on the DF70/80/90 in August 2008, subsequently added to the new DF60 and soon to be introduced on the new DF40A, DF50A and flagship DF300, which are available this summer, Suzuki’s Lean Burn Control System predicts fuel needs according to operating conditions.

This allows the engine to run on a more efficient fuel mixture through the use of a lean air-fuel ratio. A normal petrol engine will run with an air fuel ratio of 14.7:1, whereas a Lean Burn system can increase this as high as 19:1, which is a significant increase in efficiency. The Lean Burn process requires fuel to be injected into the cylinder at a precisely controlled rate and volume with a richer air-fuel mixture at the start of the injection cycle, assisting ignition, to a weaker one at the end.

This creates a longer burn time and a more controlled explosion of the fuel, over the full downward stroke of the piston. This in turn means that there is power over the whole combustion stroke and subsequently a more efficient and complete burning of all the fuel available; leading to more power for less fuel and less emissions.

However, the development of this innovative system was not without its problems. Controlling the changes to the air-fuel ratio was not very difficult but this in turn affected the engine’s output and could have potentially made the RPM unstable. To combat this, the team set to work on creating a new design for the shape of the combustion chamber on the new DF70/80/90, DF60 and DF40/50 in order to make the Lean Burn process smooth and stable.

Suzuki engineers have developed the computer control and fuel injection technology to achieve this and Electronics Design Engineer, Tomohiko Miyaki said, “When you are using an outboard motor you are out on the water and not only do you want power and fuel efficiency, you also want complete reliability. All our new technologies are designed, developed and tested to withstand the harsh marine environment.”

Unlike other manufacturers the Suzuki Lean Burn Control System has been developed so that it delivers these benefits over a wide operating range, providing significant improvements in fuel economy from low speed operation into the cruising range.

For example, initial tests have shown that the new generation DF40A and DF50A outboards, which will be available this summer, use 23% less fuel than the current 40hp and 50hp models, mainly in the cruising range, which is where the engine is used for the majority of the time.

Experiment and Evaluation Engineer, Ryuuji Hamada said, “I was in charge of bringing Lean Burn to the new DF40A and DF50A. The engine displacement of the new engine is larger than its predecessor. While a larger displacement would usually be disadvantageous in fuel costs, the Lean Burn system provides the new DF40A and DF50A with fuel economy that is better than the existing models.”

Engine Design Engineer, Hiromichi Takewaki added, “Fuel economy was an important focal point in developing the new DF40A and DF50A. In order to gain the improvements that we sought, we focused on optimising volumetric efficiency by using fluid analysis to optimise flow through the passageway. Combustion efficiency was improved using our most advanced fuel injection system and decreasing atomisation by 50% compared to the original DF40/50. These outboards are designed to be compact and lightweight so by optimising the weight of each part, we managed to reduce the outboard’s overall weight by 6kg (DF40ATL and DF50ATL) while increasing displacement compared to the original DF40/50.”

Suzuki’s unique Lean Burn Control System gives these new outboards a superior selling point over its competitors by providing a wide range of lean burn which enables the outboard to run on less fuel right up into the high speed range.

When combined with technologies that Suzuki already employs, such as multi-point sequential electronic fuel injection, variable valve timing, long track intake manifold and multi-stage induction, its range of mid to large horsepower outboards become a very attractive power option for leisure and commercial users alike as a more fuel-efficient outboard means reduced running costs.

Suzuki’s new generation DF70/80/90 and DF60 have been extremely well received by boat owners and the marine media alike. This has been reflected in sales and helped Suzuki to be the fastest-growing outboard brand in Europe. There is no reason to doubt that market reaction to the new DF40/50 and DF300 will be any different thus helping Suzuki gun for the top spot as market leader.

Chief Engineer, Hitoshi Matsumura said, “We are very proud of our achievements. It is very pleasing to see sales of the new generation outboards going so well with customers getting complete satisfaction and enjoyment from our products.”

Masahiro Yamamoto, Group Leader, Europe Marketing Group, Marine & Power Products said, “The development of the Lean Burn Control System demonstrates our commitment to constant improvement and innovation to deliver what the market wants in terms of exciting performance together with outstanding fuel efficiency. I must pay tribute to our team of engineers who continue to provide us with class-leading products to bring to the market place.”