Two-Stroke Vs. Four-Stroke Outboards: Advantages & Disadvantages

One topic that keeps popping up concerning outboards is the comparison between Two Stroke Vs. Four Stroke Outboards.

So much is being said about both types of engines, that it is worthwhile to take a closer look at the more delicate points of these two different types of outboards to get a better understanding of each one.

Here, we bring out the advantages and disadvantages of two-stroke Vs. four-stroke outboards to see what each type has to offer.

People tend to make generalizations about these two types of outboards. A common belief is that a fourstroke outboard has more power than the two-stroke variety.

Hence a four-stroke outboard should be the preferred choice. To begin with, this is a misconception as the reverse is true. Secondly, several factors decide which of the two types of outboards will be suitable.

A lot depends on the specific needs of the user when choosing between two-stroke vs. four-stroke outboards.

However, to get a clearer idea of which of these two types of outboards would be more suitable, you need to understand the difference between the two. But let’s first take a quick look at how an internal combustion engine works:

The Internal Combustion Engine Explained

There are two categories of internal combustion engines, spark ignition (SI) and compression ignition (CI).

While the spark of the spark plug burns the fuel in an SI engine, CI engines work on the principle of fuel which burns due to high-pressure compression.

There are four stages to the functioning of an internal combustion engine – suction, compression, expansion, and exhaust. The injection of the fuel and the release of burnt gases is controlled by valves which open and closed through rotating camshafts.

When the fuel burns, it creates a high pressure in the cylinder head which pushes the piston and moves the crankshaft.

This process is a repetitive action, and as the crankshaft is attached to the other moving parts of the engine, it causes them to move.

With outboard engines, the fundamental principle of the engine remains the same. However, depending on how the fuel burns, we classify the engine as a two-stroke outboard or four-stroke outboard.

Two-Stroke Outboards

A two stroke engine produces the suction and compression strokes of the piston in a single action. In the same way, the expansion and exhaust strokes also occur.

The expansion stroke is the stage which produces the power that drives the engine. The suction, compression, expansion, and exhaust occur in two ‘strokes’ of the piston; thus, the engine gets dubbed as ‘two-stroke.’

Four-Stroke Outboards

A four stroke engine also creates the same four stages, suction, compression, expansion and exhaust. However, in a four-stroke outboard, these four stages are distributed in four strokes of the piston, thus making it a four-stroke engine.

With two-stroke and four-stroke outboards, there is no ‘good’ or ‘bad.’ Each type of outboard has its advantages and disadvantages and which one would be more suitable for you largely depends on your particular requirement.

So, let’s get deeper into the pros and cons of each category of outboard. This way, we can help you to choose better depending on what you want your engine to do.

Advantages of Two-stroke Outboards

Added Power: Two-stroke outboards fire for each revolution of the engine instead of every other revolution as in four-stroke engines. This makes two-stroke outboards more powerful than the four-stroke variety.

More Robust: A two-stroke engine works in different orientations. This factor makes it a more robust engine than the four-stroke engine.

Less Expensive: The construction of a two stroke engine is less-complex than a four-stroke engine, making it a cheaper option.

Lighter: Also, due to being less complicated in construction than a four-stroke outboard, the two-stroke outboard is comparatively lighter.

Simpler Construction: Two-stroke engines have ports instead of valves which makes them easier to construct than four-stroke engines.

Disadvantages of a Two-Stroke Engine

Less Fuel-Efficient: Older model two-stroke outboards produce uniform power, but the engine is not as fuel efficient as a four-stroke.

Increased Pollution: Due to the addition of oil to fuel, this type of engine is also more polluting in older 2-stroke models.

Added Expense: As you need to add oil regularly, it results in extra running costs but fewer maintenance costs with not requiring regular services and oil changes like a four-stroke

Advantages of Four-Stroke Outboards

Fuel Efficiency: As all four stages of combustion are distributed over four steps instead of two, the engine runs smoother. This results in better fuel efficiency.

Silent Operation: Due to the above reason, four stroke outboards generally produce less noise than two-stroke outboards.

Added Lubrication not Required: We need to add lube oil to the fuel for operating two-stroke engines. We do not need to add oil in the case of four-stroke engines. Due to this reason, four-stroke engines are less polluting than older model two-stroke engines.

Durability: Because the speed of four-stroke engines is lower than that of two-stroke engines, these outboards last longer than the latter.

Disadvantages of a Four-Stroke Outboard

Extra Maintenance: A four-stroke outboard needs more regular maintenance and checkups than a two-stroke outboard.

Starting Issues: There is a tendency for four-stroke engines to be reluctant starters, even in warm weather. This is the reverse in the case of two stroke engines.

Added Weight: Due to a more complicated construction, four-strokes tend to be heavier than the two-stroke variety.

Factors Influencing Choice of Outboard Motors

Many factors will decide which type of outboard to use, like budget, the age of the boat and category. You also need to factor in the frequency of use and location.

For instance, a tournament angler who needs to get to a particular location fast, before the competition gets there.

A zippy two-stroke engine would fit the bill. If you use your boat for deep-sea trawling, on the other hand, fuel-efficiency would be a priority. In this case, you would probably prefer a four-stroke outboard.

You also need to consider the total money you are spending. If you have an old boat and trailer, for instance, it may not make sense to throw additional money towards an expensive four-stroke outboard motor.

This will not only over-capitalize your rig but also put an undue load on an old boat and trailer.

Exceptions to the Rule

All the above information is based on generalizations about conventional two-stroke and 4-stroke engines. However, it is worthwhile to note that advanced technology has eliminated many of the disadvantages of four-stroke outboards.

To quote a case in point, Ryan Moody, owner of a thriving fishing charter business has been using advanced two-stroke outboards for his boats for quite some time. Moody has been in the fishing field for over 30 years.

He says that the perception that all two-stroke engines guzzle fuel, are smoky and noisy is a myth that he has busted. Some of the two-stroke outboards today he says, are quieter, less polluting and more fuel efficient even than many four-stroke engines.

Moody gives an example as follows: If he ran a four-stroke engine, servicing it every 100 hours, he would service it five times a year. Each service costs $800. He has a two-stroke engine which needs a spark plug change and gear oil change every 300 hours. This, he can do himself.

So, he’s not paying $4,000 a year to maintain his two-stroke outboard. And he says, it is smoother and more fuel efficient and quieter than any of the four-stroke outboards.

According to Moody, he gets more power and torque from his two-stroke outboard as compared to a four-stroke engine of equivalent rating.

Moody’s Observations on his Evinrude Two-Stroke Outboards

Cleaner Emission

The manufacturer of the outboard that he uses is the first one to receive a Clean Air Technology Excellence Award by the EPA.

Cheap Running Costs

Moody says that his Evinrude two-stroke outboard costs are at least 50% less to maintain that a four-stroke outboard of similar capacity.

Less Noisy

He also says that his two-stroke outboard is at least 50% quieter than the early generation two-stroke engines.

Increased Torque

Moody had his two-stroke engine tested and found that it generates up to 25% more torque than four-strokes of the same capacity.

Improved Fuel Efficiency

He also tested the fuel efficiency by running his boat powered by a two-stroke engine alongside one with a four-stroke engine as a control. For the test run, while Moody’s boat consumed 34 litres of fuel, the control boat used 36 litres.

Quick Easy Starting

Two-stroke engines start with a single touch of the key even during winter.

A Final Word

Whether you’re having boat problems or just thinking of upgrading or adding a Four-Stroke or Two-Stroke Outboard Engine to your boat, we hope that this article gives you a better understanding of 2-Stroke and 4-Stroke Engines.

Knowing how they work is half the battle to help you get the best outboard engine for you.

Westshore Marine is one of bigger marine dealerships in Canada with a vast selection of outboards options available. If you have any questions or would like some help even if its helping you determine if a used boat motor is safe we can help.

You can visit us at www.WestshshoreMarine.ca for more information and access to great free tools like Trade-In Appraisals and Live Interactive Chat.