There are a surprising number of boat models on the Finnish market for which a 150-HP outboard motor is just the ticket, including the Buster Magnum that we used in our tests. The comparison test showed that it is possible to travel economically using a large outboard motor, but it is becoming harder to choose between two- and four-stroke engines, as the differences in performance and costs are quite small.This year’s list of boats on the market, compiled by Vene magazine, reveals that there are some 30 outboard engine boat models where the manufacturer’s engine power recommendation can exceed 150 HP. The average power of outboard motors sold in Finland has taken some time to increase to the present 20 HP, but the rate of increase has become faster during the last few years. Both engine technology and boats have developed, and increasingly, a more powerful engine is chosen for a boat now, than would have been normal a few years ago. A good example of this is the increasing popularity of 60-HP motors when compared to 50-HP models. Internationally, the 150-HP class is among the hottest.

There is a similar trend with regard to engines over 100 HP, which are considered quite large in the Finnish market. More and more boats can take a heavy engine weighing over 200 kg, and they can be run at ever-higher speeds. Whether or not this is a healthy development is another matter, but according to the accident statistics, it is not an area of concern, and the responsibility remains with the boaters themselves. The developments, however, have caused some people to start wondering whether boating is becoming an extreme sport.

During the last 10 years, four-stroke outboard motors have made a strong breakthrough. On the two-stroke front, the models with modern direct injection are also gaining ground. Half of the manufacturers of 150-HP outboards offer both two- and four-stroke engines. Yamaha already does so and Mercury intends to do so soon. In contrast, Bombardier only has a two-stroke model (plus the 140-HP four-stroke that Suzuki is about to introduce), and Honda only has a four-stroke engine. The situation is interesting.

The Finnish market for 150-HP outboard motors is small at present but on the increase. We are talking about a few hundred engines annually which in itself is a huge increase when compared to the situation 10 years ago. It is difficult to accurately estimate market shares because the sale of Yamaha and Honda four-strokes has only just begun, and Mercury’s four-stroke is yet to arrive. The two-stroke models with direct injection, the Evinrude DI (formerly called Ficht and Ficht RAM), the Mercury Optimax and the Yamaha HPDI (model Z150) have been on the market for some time.


Vene magazine was the first in the world to test all four-stroke and new two-stroke 150-HP outboard motors in the cold weather of last autumn. The conditions were not the optimum for engines that have had their settings optimized for an ambient temperature of 20°C, but at least they were the same for all. The outside air temperature varied from 0.4 to 9.6°C, luckily there was no wind – the calmer the weather, the more accurate the measurements. Water temperature varied from 4.8 to 7ºC. Because of the cold weather, the engines were all run until warm before starting the measurements. Cold weather does not reduce the power of engines as such; on the contrary, it increases the amount of air-fuel mixture in the cylinder, and the cold water under the boat slightly increases the speed. But the cold cooling water may in some cases prevent the engine from warming up to its normal running temperature. The motors (+ Suzuki DF 140) were test run and measured using the same Buster Magnum boat. After each test run, the boat was hoisted up and Jukka Laitinen of Jack Marine changed the engine. The importers’ representatives were also available to assist when required.

The tests were run with two persons and the measuring instruments aboard. The fuel tanks contained an average of 100 litres. The fuel amounts varied by about 20 to 30 litres, which dos not significantly affect the results, given that the total weight was some 1,300 kg. Our dynamometer test bench cannot handle these horsepower ratings, so power comparisons are only based on the measured performance figures.

Fuel consumption was measured using a Micro Oval II flow-through meter which was checked to be accurate to <1%. Speeds were measured using a Stalker ATS radar and a Garmin GPS 76 navigator. The noise levels were measured using a Brüel & Kjaer 2226 dB meter. One of the critical factors when measuring fuel consumption is the engine rpm. For this, we relied on the digital displays supplied with the motors, when available, but we also took inductive measurements using a Fluke 88 Multimeter, and even used a conventional vibration-resonance device.

The accuracy of engine speeds was at least ±50 rpm; it is difficult to keep the revs constant with any greater accuracy, but in most measurements the accuracy was ±20 rpm, however.

As with tests in general and boat tests in particular, the results are very much affected by ambient conditions. The results of this test will only apply to the Magnum Buster under these conditions. Different results might be obtained in the summer using a different boat, but the test does, nevertheless, demonstrate those relative differences between the engines that are likely to remain the same even under different conditions.

The starting point for the test was one of the familiar direct injection engines versus the new four-strokes. Modern two-strokes have very little relationship with the older-technology two-stroke used on boats in the past. Nowadays, although it’s all direct injection, and carburettors are history, a very interesting aspect of this test is the fact that all the tested two-strokes use a different fuel injection technology.

The number of strokes does not, however, determine the order of merit with respect to fuel consumption, speed or noise.

The results for all these parameters varied with regard to the number of strokes. Further, one engine might have a lower fuel consumption than the next on low revs, but the situation might be reversed at the ‘magic’ speed of 30 knots. Indeed, 30 knots proved to be a 'magic point' in this test. When plotting the consumption in litres per nautical mile versus speed for all five engines, the graphs coincide at this speed. The fuel economy graphs run separate at speeds both below and above the 30-knot mark, but at that speed all engines had a consumption of approximately 0.9 litres per nautical mile.

We endeavoured to have the top revs of all engines within the recommended range, but did not quite succeed.

The Yamaha F150 was running at 5,000 rpm, which is the lower end of its specified range of 5,000 to 6,000 rpm, while the Honda was running at 6,150 rpm, above its similarly specified range of 5,000 to 6,000 rpm. The Yamaha’s propeller had too large a pitch, 21 inches, which increases speed and reduces fuel consumption but is sensitive to boat weight. Honda’s situation with a propeller of too small a pitch and a gear ration of 2.15 was the opposite — it had lower speed and higher consumption but handled the boat weight very well. The two-strokes had more suitable propellers, and they have in principle better torque ratings anyway.

The Yamaha Z150 was the fastest outboard motor. It reached a top speed of 44.1 knots, 0.3 knots more than the Yamaha F150. One of the secrets behind the high top speeds of both Yamahas is the excellent 21-inch propeller. The others had a 19-inch propeller. Raising the engine by two holes as specified by the importer also increased the speed. The other engines were only raised by one hole, once again as specified by the importers. Raising the engine usually slightly increases the speed but may have adverse effects on other properties, such as behaviour in tight turns and overall handling. In this test, we did not investigate whether the propellers would cavitate in tight turns.

Both Yamahas needed the lowest revs for the speed, which in itself is proof of the advantageous propellers and gear ratios. The gear ratio of the Z150 (1.86:1) is no different from the other two-strokes (Evinrude 1.86:1 and Mercury 1.87:1), but the difference with the four-stroke models of Yamaha (2.0:1) and Honda (as much as 2.17:1) is quite clear. Therefore, the Honda would need the highest revs for a given speed if all were using the same propeller.

At full throttle, the Evinrude ran at 41.7 knots and the Mercury at 41.1. Due to its propeller, the Honda was the slowest at 40.5 knots. A propeller with a slightly larger pitch would have dropped the revs by 200 to 300 while increasing the top speed.

Magnum started planing at around 10 knots with all engines — this is a typical property of this particular boat model. Acceleration was very good with all these engines. The Yamaha Z150 achieved the fastest unofficial acceleration figures with the Mercury not far behind, but the actual differences between the engines were based more on gut feeling than fact, and were in any event a few seconds at most.

The noise measurements produced two distinct groups: at idling speeds and slightly above, the four-stroke engines were significantly less noisy than the two-strokes. When speed was increased, the Yamaha Z150 joined the four-strokes while the other two-strokes were in a category of their own.

While the noise level of the Yamaha F150 and the Honda BF150 below the planing threshold, at 8 to 9 knots, is only some 71 dB(A), the reading for the Yamaha Z150 is 73 dB(A) while both the Evinrude and the Mercury can be as much as 76–78 dB(A).

At 20 knots, the Yamaha F150 produces a level around 75 dB(A) while the reading for the Z150 and the Honda is 76 dB(A). At 30 knots, all of the engines, with the Honda last, reached the 80-dB mark. The critical 85-dB reading is first reached by the Mercury at just 20 knots.

At the most economical speed, the Yamaha F150 is the quietest of the motors, followed by the Honda and the Yamaha Z150, while the Mercury is the noisiest. The Yamaha F150 was also one of the two engines that produced the loudest noise of 90 dB(A) at full throttle. The Yamaha Z150 was slightly quieter at 89 dB(A), while the Honda and the Evinrude were clearly so at 86 dB(A).

Below are listed the speeds at which each engine reached the highest permissible continuous noise level (over 20 minutes) of 85 dB(A), measured at the ear level of the Magnum pilot.
Evinrude 150 DI Honda BF150 Mercury 150 Optimax Yamaha Z150 Yamaha F150	38 knots 34 knots 20 knots 41 knots 42 knots

150-HP outboard motors consume fair but not outrageous amounts of fuel. At full throttle, all burn over 50 l/h, but only the Mercury reached the 60 l/h mark, albeit only just (60.6). However, the gap to the Evinrude (51.8 l/h) was considerable. The Yamaha Z150, the third engine with direct injection, consumed 54.9 l/h, i.e. it was the second least thirsty.

A peculiar exception in fuel consumption figures at idle speeds was produced by the Yamaha Z150, which needed twice as much fuel as the next engine, 3.3 l/h. This was not a measurement error, because this exceptional figure was obtained several times. The Evinrude, Honda and Mercury engines all stayed near 1 litre at their idling speeds of 550 to 650 rpm. The four-stroke Yamaha needed 1.6 litres.

The economical running speed of 150-HP outboard motors was in the 3,000 to 3,500 rpm range. The typical boat speeds at these revs were 20 to 30 knots, which are pleasant cruising speeds. At 3,000 rpm, there were considerable differences in fuel consumption figures between the different motors, even disregarding the Honda which needed higher revs than the others. The highest consumption at 3,000 rpm was measured for the Evinrude, 21.8 l/h, and the lowest for the Mercury, 14.5 l/h. The Honda’s reading was 8.8 l/h. When increasing the revs to 3,500, the differences remained the same, except that the consumption of the Yamaha Z150 was the highest.

The consumption figures expressed as litres/hour are relevant when boating with the intention of just spending time on the boat, as is often the case in the open coasts of the south. The situation is different when one has a fixed destination, as we often do. Then fuel economy, expressed as litres per nautical mile, becomes the key issue. The order of these engines changes when speed is also taken into account in the consumption figures, and the economy of the boat-engine combination calculated. That is often a more meaningful figure than fuel consumption per hour as it tells you the amount of fuel required for travelling one nautical mile.

The Honda BF150 was the most economical when moving the Buster Magnum; it was the only engine to clock a figure of less that 0.7 litres/nautical mile (0.68, actually). The four-stroke Yamaha (0.72 l/n. mile) and the two-stroke Mercury (0.71 l/n. mile) also came close. The differences between these boats are only in the second decimal place, i.e. in centilitres. The Evinrude had the highest consumption per nautical mile (0.9 l/n. mile). Hence, the engine that has the lowest consumption at full throttle actually consumes the most per nautical mile. The Yamaha Z150 was in the middle ground with a figure of 0.82 l/n. mile.

When running at idling speed, the motors were quite economical, with the exception of the two-stroke Yamaha (1.2 l/n. mile). The Evinrude travels a nautical mile with the least amount of fuel, 0.4 litres. The Honda and Mercury engines also come close to 0.4 litres, while the Yamaha’s four-stroke needs 0.55 l/n. mile. At engine idling speeds, the Buster travels at speeds ranging from 2.3 knots (Honda) to 3.2 knots (Yamaha Z150), a most suitable speed range for troll fishing.

If you have 100 litres of fuel, one of the engines will take you and your Buster a distance of 147 nautical miles while another will only travel 111 nautical miles. With one of the engines, the trip takes 7.5 hours while another takes less than 5 hours.

The slowest takes 3 minutes and 27 seconds to travel 1 nautical mile and the fastest takes 2 minutes and 21 seconds. Therefore, there are significant differences in economy, and they do not follow the two-four stroke divide.

Using one hundred litres of fuel: n. miles time (h:min)

Evinrude 111 6:23

Honda 147 7:30

Mercury 141 6:54

Yamaha Z150 122 4:47

Yamaha F150 139 6:00

When calculating fuel economy, one has to bear in mind that two-strokes also consume oil when running. Four-strokes only need oil added during maintenance. The cost of oil (oil + filter) for a four-stroke is 60 to 70 euro/100 hours or season. In contrast, two-strokes consume oil as you run them. The oil consumption of two-strokes varies with many factors, but for example, the oil consumption of the Mercury Optimax varies between 0.4 and 2.5%. Calculating its average oil consumption, we arrive at a figure of 1.7% of the amount of fuel. This figure is between 1 and 2% for all these two-strokes. Therefore, it takes approximately 1.5 litres of oil to burn 100 litres of fuel at cruising speeds, and this oil costs between 6 and 10 euro/litre, depending on the brand.

Each model has its own strengths Rated consumption ICOMIA (the International Council of Marine Industry Associations) has quite an important role as a counterpart for the EU directive bureaucrats, providing expert opinions to assist in the work for creating official norms for the industry. ICOMIA has surveyed the usage of boats in different countries and used the results to create a sort of average boater's 'typical driving pattern' that is used for calculating the rated consumption. Equally, it could be used for calculating rated noise levels and rated economy.

The rated consumption is a weighted average of consumption figures, weighted using the typical driving pattern, and the measurements are taken at five different speeds, ranging from full throttle (100%) down in 20% increments to 20% of full throttle engine speed. The survey suggests that full throttle is used 6% of the time, while the subsequent lower measurement revs are used 14, 15, 25 and 20% of the time, respectively. In other words, ICOMIA assumes that the average boater uses the throttle lever rather conservatively, which is why the small consumption figures at low revs are more important.

Nobody is exactly an average boater, but the said distribution of running speeds is not unrealistic in our conditions, particularly if one observes the speed limits in harbours and sheltered waterways. Trolling and other fishing types also use low revs a lot.



Rated consumption figures

Evinrude 150 DI 18.8 l/h

Honda BF150 15.7 l/h

Mercury 150 Optimax 17.3 l/h

Yamaha Z150 20.0 l/h

Yamaha F150 18.5 l/h

Economy ranges Less than 0.7 l/n. mile knots

Honda BF150 13-23

Less than 0.8 l/n. mile

Honda BF150 11-27

Mercury 150 Optimax 14-26

Yamaha F150 16-25

Less than 0.9 l/n. mile

Evinrude 150 DI 17-18

Honda BF150 9-29

Mercury 150 Optimax 11-29

Yamaha F150 14-28

Yamaha Z150 17-27

Less than 1.0 l/n. mile

Evinrude 150 DI 15-33

Honda BF150 0-30

Mercury 150 Optimax 0-31

Yamaha F150 12-30

Yamaha Z150 14-31

All these engines use state-of-the-art technology. The oldest motor is the Evinrude, which was initially introduced in the mid-nineties. A lot has happened since. The first Ficht generation was replaced by the new Ficht RAM, and now the new owners of the company have considerably extended the development work and the motor functions without problems.

The Yamaha Z150 is a few years old, as is the Mercury Optimax, whereas both of the four-strokes are brand new models. The Yamaha was introduced last spring, and the Honda in the autumn. Their sales have only recently started, but one can confidently forecast success for both.

This comparison test did not focus on the technical differences of these engines as they have already been presented in other contexts. This test was about performance, and indeed there were some clear differences. The engines’ properties are to a degree contradictory, but if you know your own boating pattern and are honest with yourself about which factors are really important, these differences will actually make choice that much easier, at least as far as the significant differences are concerned. In some cases, though, the differences only appear in the second decimal place in which case they offer very little to go by.

Regarding the issue of two-strokes versus four, the four-strokes did a little better as a whole, unless we count in Honda which would have been faster when fitted with a more suitable propeller.

The four-strokes were economical and quiet. As evidenced by the comparison of winter maintenance costs published in the 12/03 issue of Vene magazine (p. 34), four-strokes are more economical than two-strokes. The said comparison was between Mariner and Mercury, but the general result is the same with other brands also.

It is impossible to give a simple verdict regarding whether one should buy a four- or a two-stroke. The differences can more easily be found between different brands. Price is a major factor. The least expensive motors in the test (Evinrude and Yamaha Z150) cost 14,900 euro, and the most expensive (Honda) costs 16,900 euro. The 2,000-euro price difference will buy you approximately 1,500 litres of petrol and 20 litres of two-stroke oil in a marine service station. The Yamaha F150 is in the middle of the field with a price tag of 15,900 euro. All these prices include remote controls, meters and a propeller.

Here, the Mercury differs from the others. It also costs 14,900 euro, but the price only includes the propeller. Remote controls and meters have to be bought separately. The basic meters and remote controls will set you back 400 euro. The reason for this practice is the increasingly popular approach where boat builders install their preferred makes of meters and remote controls during manufacture, with the result that the boat will be restricted to using a certain make of engine, but it can be installed by the dealer quickly and without problems.

Alongside four-strokes, the two-stroke engines have also developed rapidly during the past few years. In particular, the American regulations for reducing exhaust emissions have forced outboard motor manufacturers to start using new technologies. For two-strokes, this in practice means direct fuel injection.

Back in the old days, the technology was altogether different two-stroke engines had carburettors. Fuel was combusted inconsistently, and plenty of unburned hydrocarbons, i.e. fuel and oil, used to escape into the water and the air.

But times have changed in boating too. People have become aware of environmental pollution, primarily in California, USA; pleasure boating is quite popular in the US, even in waterways that act as the source of drinking water for millions, and, naturally, people concerned about environmental and health issues prefer to drink clean water. When matters are stirred up in the US, the consequences are first felt in Japan and some time later in Europe.

Now we have four- and two-stroke outboard motors with direct injection. Even though conventional two-strokes are still being manufactured, they are sold to developing countries and other markets that are less concerned with environmental protection than Europe and the US.

Nearly 70% of new outboard motors sold in Finland are four-strokes. Some old-style two-strokes are still being sold while it is still legal, but these are being replaced by the new two-strokes. Today, the smallest direct injection engines have 70 HP, but smaller models are on the horizon. Rumour has it that Bombardier has been continuing the development work, initially started by OMC, for a 2-HP direct injection engine.

There are three brands offering direct-injected two-stroke outboard motors on the market. Each of them uses a different technology for fuel injection: the Mercury Optimax uses the original Australian Orbital system, Yamaha has its proprietary HPDI, and Bombardier relies on the original German Ficht technology, albeit preferring not to call it Ficht any more. After the acquisition of Ficht and OMC by Bombardier, the name is now DI.

In all direct injection technologies, fuel is injected into the combustion chamber as a pressurized, atomized spray.

The methods differ with respect to the pressure used: the Yamaha uses a pressure of nearly 5 MPa, while others require a much lower pressure. The Orbital requires 621 kPa and the Evinrude DI 201 kPa. The Evinrude pressurizes the fuel in the injection nozzle, so there is no need for a separate compressor. Intake air is not pressurized; it enters the cylinder in the conventional manner through the crankcase. Fuel is injected directly in the combustion chamber when the intake and exhaust channels are closed. The nozzle injects fuel up to one hundred times a second.

Optimax differs from the others in that a pressurized mixture of fuel and air is injected in the combustion chamber with the exhaust channel closed. The fuel is pressurized using a fuel pump and the air using a separate compressor. They are combined in the computer-controlled pump nozzle. Oil is not mixed with fuel but injected directly to where lubrication is required.

In Yamaha's HPDI (High Pressure Direct Injection) system, fuel is pressurized using a separate compressor and then channelled to the electronically controlled pump nozzles. Fuel is injected into the combustion chamber a fraction of a second before the exhaust channel is closed. Air enters the cylinder via the crankcase. As the piston compresses the mixture of air and injected fuel, it causes a vortex in the semi-spherical combustion chamber.

All direct injection systems are computer controlled. The computer regulates the amount of fuel and the timing of injection by monitoring several parameters, such as throttle lever position, ambient air temperature, engine running temperature, etc. The HPDI system also has a Lambda sensor for monitoring the oxygen content of air.

The test runs were conducted using a Buster Magnum which was hoisted up between runs, and the engine was removed and replaced with the next one. In all, we hoisted and launched the boat 15 times.

When the air temperature is near zero, things are tougher on the testers than on the engines. Adequate clothes help!

Fuel consumption was measured using a flow-through meter, which in most measurement ranges is accurate to less than 0.5%.