In the outboard motor market, it is difficult to make your product stand out from the competition. In the large BOOTE comparative tests, however, we always point out strengths and weaknesses in terms of consumption, noise and acceleration. The latter is measured in the time it takes to reach a certain speed, and the results can vary by a few seconds. However, outboards with the same performance are otherwise very similar. None is outstandingly more powerful than the others, and none is particularly weaker.
When developing the new engine series between 75 and 115 hp, the Japanese manufacturer Tohatsu set itself the major goal of setting itself apart from the market. But how? Should the new engines be even more economical or quieter than those of the competition? Economical and quiet too, of course. Above all, the new engines should have the highest torque in their class over the entire speed range, reach their top speed as quickly as possible and thus reach their maximum speed. The bottom line: to be the engines with the best acceleration.
Need more information? You can find the test of the Tohatsu MFS 115 with technical data and more pictures in BOOTE issue 03/2021 from 17 February 2021 at newsstands or online at Delius Klasing Shop.
However, the developers wanted to override the old rule that "there is no substitute for displacement" - because adding more displacement to the engine would mean making it significantly heavier, and weight is always a disadvantage. So they asked themselves how they could increase the performance of the engine without increasing the displacement and found another way: "Why not design an exhaust manifold that has never been used on an outboard engine before?"
The task of an exhaust manifold is to dissipate the exhaust gases as effectively as possible. If a manifold is well designed, it can significantly increase performance, especially in the lower engine speed range. Tohatsu calls the result of this lengthy development process "4-2-1 Performance Tuned Exhaust", a geometrically optimised exhaust system. Instead of merging all four exhaust manifolds into one exhaust pipe as usual according to the 4-1 concept, the exhaust ducts of cylinders 1 (top) and 4 (bottom) and those of cylinders 2 and 3 are first merged into two exhaust pipes. These two exhaust pipes then flow into a common pipe. This is a concept that has long been familiar in the tuning scene for older cars, but is very unusual in this form for outboards. However, Tohatsu has further developed and optimised the concept.
Merging using the 4-2-1 method with exhaust pipes of completely equal length creates a suction that intensifies the exhaust gas flow out of the engine. Put simply, the pistons do not have to struggle to push the exhaust gases through the valves to the outside; a vacuum supports them in the process. In practice, this simple but intelligent change creates impressive acceleration behaviour, and the engine actually reaches its final speed more quickly.
We test drove the new 115 hp model on the Elbe and were impressed by the power control, especially in the rev range between 3500 and 4500 rpm. The high torque is clearly noticeable there. The acceleration feels different to anything familiar from four-stroke engines of the same size: the boat pulls its nose up for a moment, then immediately drops back down and literally takes off. The test boat, a Valiant V-570 RIB, reaches a speed of 50 km/h after 6.7 seconds and continues to accelerate to a top speed of 72 km/h without any major reduction.
Need more information? You can find the test of the Tohatsu MFS 115 with technical data and more pictures in BOOTE issue 03/2021 from 17 February 2021 at newsstands or online at Delius Klasing Shop.
In fact, Tohatsu has succeeded in fulfilling all the specifications it set itself: The Tohatsu MFS115 AETL is well below or in the midfield between the Yamaha F115 (2.1 l, 163 kg), Yamaha F115B (1.8 l, 177 kg), Suzuki DF115A (2 l, 187 kg) and Honda BF115 (2.3 l, 220 kg) in terms of both displacement and weight (2 litres, 182.5 kg). It therefore offers the best torque-to-weight ratio. Due to its small cubic capacity, the engine is also extremely economical. In the speed range between 3000 and 3500 rpm, it consumes just 0.32 or 0.35 litres of petrol per kilometre, which gives it a theoretical range of 304 kilometres (tank filling: 100 litres) at a good gliding speed. At full throttle, the engine requires almost twice as much fuel (0.62 litres/kilometre), which is also perfectly acceptable in comparison. Tohatsu has also made improvements in the area of engine electronics: The new 4.3-inch LCD display is connected to the engine's CAN bus and communicates all engine data, error codes and alarms in a very clear and modern design.
