Two stroke – against four (Test of Honda BF 90, Tohatsu 90 TLDi motors)

Both outboard motors came from Japan and both settled in the 90-strong class, but the similarities between Honda BF 90 and 90 Tohatsu TLDi ends on this.
Mid-December in Hamburg was held under the motto: “2-stroke outboard to 4-stroke.” What are the strengths and weaknesses of the representatives of the family of internal combustion engines?

Installed on board «Hellwig Marathon V485», both representatives of a class could come up against each other on equal terms.

Honda BF 90

Technique with a four-stroke engine BF 90 is widely known, however, Honda has led to “four-stroke” sensation in the world of boats with outboard motor.

The power unit BF 90 is borrowed from the famous car Honda Civic. Modified to work on the body of water the engine, the volume of 1590 cm 3, has a capacity of 66.2 kW (90 hp..).

The maximum speed for four-cylinder 12-valve engine is between 5000 and 6000 rev. / Min. The argument for the use of four-stroke engines is, above all, the absence of impurities in the fuel oil, so it is easier to comply with the increasingly stringent emission standard.

This four-stroke engines compare favorably with conventional two-stroke engines is obviously softer operation, less noise and economical consumption of expensive fuel.

The disadvantage, manifested in the equipment of small boats is quite a lot of weight, which in a dry state, ie, without oil, from Honda BF 90 in the extended version is 174 kg.

Tohatsu 90 TLDi

Represented in Germany by «Volvo Penta Central Europe» Tohatsu outboard motor 90 TLDi has a dry weight of 129 kg.

TLDi here means “low emissions, direct injection”. Those. is injected into the combustion chamber is not a mixture of gasoline and oil, known to us by classical fuel supply system of the two-stroke engine, and clean fuel, as in four-stroke engines.

The required quantity of oil accurately dosed and fed directly into the crankcase. If you are still used for this mechanical oil pump, the new line has been replaced by Tohatsu electric.

Another feature of the outboard motor Tohatsu is the compressor. It pumps the intake air to the injector, which, depending on the number of revolutions up to 100 times per second fuel mixture is created, and then was injected into the cylinder.

Using this technology, outboard motors of Tohatsu TLDi satisfy both American standards of the US Environmental Protection Agency, which will come into force in 2006, and even more stringent California requirements of CARB.

Hellwig Marathon V 485

This 6-bedded dinghy from Erkelenz has a length of 5.08 m, a width of 1.99 m and its weight without engine 430 kg.

A detailed report about all the diversity of the German manufacturer of design you can read in the September issue of the magazine “Skipper” for 2001.

As additional equipment the boat, launched in Hamburg, was built in 80-liter fuel tank with an electric shut-off valve. A huge beach chair available has not received even the crew look at the temperature just above the freezing point.

Propellers

The test was attended by representatives of both companies outboard engines: Honda engine was equipped with a propeller made of stainless steel screw and regular screw Tohatsu was aluminum.

To equalize the chances, we conducted a series of different measurements, equipping engines propellers brand «Turning Point» American manufacturer of «Express».

The main feature of these screws – removable hub, which means that the hub is supplied for a particular engine and propeller can be selected separately.

In this case the screw assembly in comparison with screws made in the traditional way, it turns out significantly cheaper. The new hub is required only after a very strong impact on the bottom.

Turning Point of American producer program offers propellers for all common brands of motors, both for stationary and for hanging.

The testing of the selected boat motors is important that the driving force of the care one screw.

Practice

Overcast skies, drizzling rain at times, not ideal conditions for travel by motor boats. The boat was a crew of two, the tank was filled by a quarter, which corresponds to about 20 liters of gasoline.

With the necessary equipment on board Hellwig Marathon V 485 with engine Honda BF 90 I weighed about 825 kg, with motor Tohatsu 90 TLDi – about 780 kg.

With steel standard screws size 13 ¼ x 18” Honda reached the maximum speed of the day – 36.6 knots.

Tohatsu Marathon disbanded its regular aluminum screw size 13 ¾ x 17” up to 33.4 knots. After numerous rounds and adjustments, both outboard motors were equipped with Express screws made of stainless steel, size 13 ¼ x 17”.

There Tohatsu at all engine speeds was ahead, even at 3000 rpm. / Min. -on much as 8 knots more!

But at a maximum speed of both cars in what each other have not conceded.

Tohatsu steel screw reached 36.4 knots at 5400 rev / min, Honda -.. 36,3 knots at 6200 rev / min.. The difference of 0.1 unit in everyday use will not play a significant role.

Rather then have the exhaust noise!

If Honda produces at maximum speed in place of the steering hasteless sounding 85 dB (A), the Tohatsu buzzing in the ear steering, stated publicly 96 dB (A).

Then, test the engines proved themselves during acceleration from four to 18 knots: the multiple measurements stopwatch stopped at around 4 seconds.

What to choose?

Two stroke or four. In whose favor to make a choice?

Emission standard, which will be presented in the future easily fulfill both machines, the speed and acceleration of each other, they do not give way under the condition that the screw has been properly matched.

The level of noise Tohatsu showed himself a typical representative of two-stroke engines. A few dB would it hurt to remove it!

The title, by virtue of its design, it saves compared to Honda 45 kg and stands in Germany around 1280 euros cheaper than its rival four.

According to the materials of the test conducted by the experts of the German magazine «Skipper»