Nov 04, 2010 Re: 2 stroke vs. 4 stroke for a 9.9 yamaha When it comes to portaging, that means weight and 11 pounds is not insignificant. Four strokes also need to be transported vertically or one one specific side and that side only to prevent engine oil from getting into places it doesn't belong. 2-Stroke vs 4-stroke Engine Preference Survey Hi, I am a student in college and I am conducting a research assignment for a technical reporting class about 2-stroke and 4-stroke engines. I would greatly appreciate if you could take a few minutes and answer these few questions.
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.
![Yamaha 9.9 4 stroke manual Yamaha 9.9 4 stroke manual](/uploads/1/2/5/8/125827035/691923421.jpg)
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.
Automotive engines have transformed over the years, but two main gasoline powered combustion engine designs remain: the 2-stroke and the 4-stroke. While we’re sure you’ve at least heard these terms before, do you really know the difference between them? How do they work, and which is better? Read on to learn the answers!
How Do Combustion Engines Work, and What Is A “Stroke” Anyways?
In order to understand how these two engines are different, you first need to become familiar with the basics.
During an engine’s combustion cycle, the piston moves up and down within the cylinder. The terms “top dead center” (TDC) and “bottom dead center” (BDC) refer to the piston’s position within the cylinder. TDC is its position nearest to the valves, and BDC is its position furthest from them. A stroke is when the piston moves from TDC to BDC, or vice versa. A combustion revolution or combustion cycle is the complete process of gas and air being sucked into the piston, igniting it, and expelling the exhaust:
- Intake: The piston moves down the cylinder allowing a mixture of furl and air into the combustion chamber
- Compression: The piston moves back up the cylinder; the intake valve is closed to compress the gasses within
- Combustion: A spark from the spark plug ignites the gas
- Exhaust: The piston goes back up the cylinder and the exhaust valve is opened
Difference Between A 2-Stroke & A 4-Stroke
The Difference between a 2-stroke and a 4-stroke engine is how quickly this combustion cycle process occurs, based on the number of times the piston moves up and down during each cycle.
4-Stroke:
In a 4-stroke engine, the piston completes 2-strokes during each revolution: one compression stroke and one exhaust stroke, each being followed by a return stroke. The spark plugs fire only once every other revolution, and power is produced every 4-strokes of the piston. These engines also do not require pre-mixing of fuel and oil, as they have a separate compartment for the oil.
Watch this quick video for a further description of how the 4-stroke engine works:
2-Stroke:
In a 2-stroke engine, the entire combustion cycle is completed with just one piston stroke: a compression stroke followed by the explosion of the compressed fuel. During the return stroke, the exhaust is let out and a fresh fuel mixture enters the cylinder. The spark plugs fire once every single revolution, and power is produced once every 2-strokes of the piston. Two-stroke engines also require the oil to be pre-mixed in with the fuel.
Watch this quick video for a further description of how the 2-stroke engine works:
Pro’s and Con’s:
So, which is ‘better’? Here are a few of the pro’s and con’s to both engine designs:
- As far as efficiency goes, the 4-stroke certainly wins. This is due to the fact that fuel is consumed once every 4 strokes.
- Four-stroke engines are heavier; they weigh upwards of 50% more than a comparable 2stroke engine.
- Typically, a 2-stroke engine creates more torque at a higher RPM, while a 4-stroke engine creates a higher torque at a lower RPM.
- The 4-stroke engine is also much quieter, a 2-stoke engine is significantly louder and has a distinctive, high-pitched “buzzing” sound.
- Because 2-stroke engines are designed to run at a higher RPM, they also tend to wear out faster; a 4-stroke engine is generally more durable. That being said, 2-stroke engines are more powerful.
- Two-stroke engines are a much simpler design, making them easier to fix. They do not have valves, but rather ports. Four-stroke engines have more parts, therefore they are more expensive and repairs cost more.
- Two-stroke engines require pre-mixing of oil and fuel, while the 4-strokes do not.
- Four-strokes are more environmentally friendly; in a 2-stroke engine, burnt oil is also released into the air with the exhaust.
Two-stroke engines are typically found in smaller applications such as remote-controlled cars, lawn tools, chainsaws, boat motors and dirt bikes. Four-stroke engines are found in anything from go-karts, lawnmowers and dirt bikes, right up to the typical internal combustion engine in your vehicle. It’s up to you to decide which engine you prefer, and for what purpose.
At Berryman Products, we are committed to providing prompt personal service and producing products that meet the highest quality standards of performance, reliability and environmental responsibility. Check out our website andFacebook page for accurate information and quality products you need to handle your most common vehicle issues.