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2 stroke vs 4 stroke outboard – Difference Between Two Stroke and Four Stroke Engine

With the anti-pollution standards applicable to outboards, engine manufacturers adopt new technologies. These powerful and ecological innovations are often unclear for the boater. To see more clearly, here are the elements that will help you choose your next engine.

How much has been traveled, the ancestor of the outboard, invented by Baron Gaston Trouché in 1908! Today, the term outboard is inseparable from those of injection, electronic management, low emissions, four and two times. It is the four-stroke technology that currently dominates the market in Europe and the United States, with nearly 80% of sales. This is a shift taken a few years ago by the industry, who felt that four times was the best way to meet environmental standards. The Evinrude E-Tec and Mercury OptiMax engines show the perfect viability of the two-stroke direct injection engine, and sobriety that has nothing to envy to his rival. choosing not only the 2 or 4 stroke engine is important but also buying the best outboard engine is also important.
The current trend in outboard is the resumption of the race to power. In 2000, we were ecstatic about the 225 hp four-stroke Honda, we arrived today, at Mercury and Yamaha, at 350 horsepower for pleasure engines. Indeed, outboard motors of 300+ horsepower had existed for a long time, but they were the preserve of competition and were not viable for recreational use. Three hundred horses became a critical threshold for speedboat manufacturers. There is a real market for this power, especially in the United States to equip, among others, fast fishing boats, open or fishing, as well as big day-cruisers. Three hundred and fifty horsepower is the modern Everest powerboat speedboat. To reach this threshold, Yamaha does has not hesitated to develop a V8 architecture in a block of more than 5 liters of displacement! An outboard V8, who would have bet on it even two years ago? To clear this affront, Mercury unveiled the hidden virtues of its 6-cylinder in-line compressor, the Verado, which also reaches this symbolic bar of power. This frantic quest for “always more” might seem absurd but, again, there is a real market across the Atlantic.

What’s more, with these big mills, the manufacturers clearly show their ambition to steal market shares with Z-drive inboard engines. The four-stroke works, as its name, suggests, in four phases: admission, compression, combustion and exhaust. The energy is produced during the motor time (relaxation), the other three times are energy consumers. It also takes two crankshaft revolutions to complete a cycle, with only one spark.

Direct injection

Which exists in the four-stroke petrol automobile, has not yet been developed on marine engines, whether it is outboard or inboard. Indirect injection type EFI today leaves enough room for engine manufacturers to meet the requirements of the EU, EPA and Carb standards on the environment.
Nobody will say the opposite: the four-time remains to this day the most silent of the two idling technologies. This is probably why it is acclaimed by trollers, who are driven to sail for a long time at low speed. Long considered to be unsuitable for trolling, the two-stroke is now more stable than before at idle, thanks to direct injection. Some two-stroke engines, particularly at Mercury, even offer idle speed control directly from the cockpit, thanks to the SmartCraft control panel, which makes it possible to fine-tune the drag speed, for example.

The four times:

It is known to be linear in their acceleration compared to the two beats, which release their torque on a smaller range. The progress made with electronic management, ignition mapping control and variable length intake and exhaust systems has made it possible to erase these overly strong character traits. What we are looking for on an outboard engine, and on a marine engine in general, is a significant torque at low speeds to plan quickly (except of course in the case of a semi-planing hull or to shifting). The two-stroke is marginalized, but it continues to evolve technologically with the E-Tec and OptiMax engines. We talk about two times, because the admission and compression times co-occur, like those of combustion and exhaust. As a result, a crankshaft revolution is enough to complete a complete cycle. This means that, in theory, the two-stroke has a much higher return. The arrival of injection, electronic management, V-Tec and VVT technologies (Honda and Suzuki) playing on valve opening times and cam profiles, as well as the compressor at Mercury, helped overcome the indolence of the four-stroke to achieve performances comparable to those of two-stroke, sometimes even higher.

Advantages of 4-stroke engines

  • Low pollution, complies with all standards.
  • Good power at high speed and good acceleration.
  • Low fuel consumption.
  • Quiet.
  • Engine management systems.
  • Electronic ignition systems.
  • Lubrication is done by the oil that is added to the engine rather than the gasoline and oil mixture. The four-stroke is, therefore, less polluting and more economical.

The two-stroke:

This engine still has an advantage, at least for transportable outboards: the absence of an oil pan allows the engine to be stored in any position, without the risk of spilling the lubricant, while the four-stroke engine time must be stored in a precise position. Although Selva has developed this year a small 2.5-stroke four-stroke oil lubricated; he escapes this constraint. 

Advantages of 2-stroke engines

  • Better acceleration at startup and high speed.
  • Excellent weight/power ratio.
  • The simple design of basic models.
  • Prices generally lower than four-stroke engines (two-stroke carburetor only).
  • No oil change.
  • Generally less than a four-stroke weight.
  • Better performance than the two-stroke carburetor (compare to four times).
  • Generally quieter than the two-stroke carburetor (compare to the four-stroke).

You also should know how to install an outboard motor on transom beacuse it will help you to run your engine properly.

Outboard and environment

Proponents of the four-stroke blame the two-stroke by saying that the engine lubricant is burned in the combustion process, resulting in the release of harmful particles into the environment. What the pro-two-time retort: “What happens to used oils four-stroke engines after emptying? According to US statistics for 2006 from the American Petroleum Institute and the EPA (Environmental Protection Agency), 17.5% of these oils are disposed of improperly. Still, strict standards have been in place to regulate pollutant emissions from outboard (and inboard) since 1990. Three standards are authoritative in environmental matters. They are called EU or RCD for Europe, Carb and EPA for the United States. They fix up to 2010 strict levels for unburned gas (HC), CO2, carbon monoxide and nitrogen oxides (NOx) releases. The so-called drastic Carb standard is specific to the state of California, but the EPA is a federal agency.

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