2-Stroke Or 4-Stroke?

2-Stroke Or 4-Stroke?

If you’re in the market for a 50cc, 80cc or even a 125cc scooter, the question of whether to get a 2-stroke or 4-stroke scooter may be on your mind. The 50cc market is loaded with models from both camps, whereas the 80cc, 110cc and 125cc markets are quite a bit more limited in this regard. Vintage Vespa’s / Lambretta’s aside, the only 2-stroke 80cc-125cc scooters sold were Honda’s Aero 80Aero 125, Yamaha’s Riva 80 and the Genuine Rattler 110. Vespa has sold small numbers of their vintage 2-stroke PX125 in recent years.

To understand this question, it’s helpful to have a basic idea of how these engines work. If you really hate technical content then feel free to skip the next two paragraphs. A 2-stroke engine is a relatively simple concept. A 2-stroke motor jams all the steps in running an engine into two ‘strokes’. A ‘stroke’ is just the piston moving up or down. So in a 2-stroke engine, the motor breathes in fresh air/gas, squishes that, ignites the mix and then expels the exhaust all in just two strokes. So this means that every time the piston is moving downward the air/fuel mix is “exploding” and the engine is making power.

A four-stroke engine takes twice as long to accomplish the same thing. The engine sucks in the fresh air/fuel mix when the piston descends, then on the next stroke it rises and compresses the mix, on the third stroke the mix is ignited and it expands and pushes the piston down. Lastly, on stroke number four the piston rises back up and pushes out the exhaust.

The reason two stroke engines are a dying breed is because they are fundamentally less efficient. A 2-stroke engine crams all the steps into a quicker process, so it can’t do as good of a job breathing in the fresh mix and exhaling the burnt gases. However, two stroke engines generally make quite a bit more power because they have twice as many power strokes. A 2-stroke engine at 8000 RPM will be “exploding” the air/fuel mix twice as often as a 4-stroke that is also at 8000 RPM. Accordingly, if a 2-stroke engine was as efficient as a 4-stroke, it would make twice the power. In reality, 2-strokes make about 50% more power than a 4-stroke of the same engine size because they are less efficient and because the design requires less stress on the motor (ie. lower compression ratios).

The other key difference is that 4-stroke engines use engine oil and require oil changes, whereas 2-strokes do not have a load of oil inside but instead they mix in a little special 2-stroke oil in with the gas which then lubricates the engine as the air/fuel mix flows through the engine.

So what advantages do 4-strokes have? They are more fuel efficient by about 25%. They also have radically better emissions, last longer and they don’t foul spark plugs nearly as much.

The advantages of 2-stroke are more power and simpler maintenance. You don’t need to adjust the valves or change the oil with a 2-stroke. All you have to do is keep oil in the oil tank and change the spark plug when your scooter starts slowing down. Normally, 4-stroke engines are better because they are more efficient and last longer. That is why all cars and virtually all motorcycles are 4-strokes. Really the only reason we still have 50cc scooters that are 2-strokes is because of legislation that favors 50cc’s. If these laws allowed 50cc 2-strokes or 75cc 4-strokes (so that power output is the same), I think we’d see almost all 4-stroke scooters. In reality, the insurance and laws are always going to favor 50cc’s which is why a 2-strokes are still sticking around.

So which should you buy? If power is your main concern then a 2-stroke is the obvious choice. Most 2-stroke 50cc’s make 5-7 hp and are artificially restricted to speeds ranging from 30-40mph. You can often easily derestrict them so they go 45-50mph. 4-stroke 50cc engine’s on the other hand are working very hard just to make about 3-5 hp and adding more power is not easily done.

Besides the power disadvantage, 4-strokes make a lot of sense. You’re getting better milage, a more reliable engine with a longer life, you’re easier on the environment and your scooter will have a nice quiet exhaust note instead of the higher pitched ‘tinging’ of a 2-stroke exhaust. I suggest that you buy a 4-stroke if you are can manage to accept mediocre power output. A modern 4-stroke 50cc scooter tops out around 37-43mph. The top speeds are actually pretty good for riding around town but the acceleration isn’t there like it is with a 2-stroke. If you ride with a passenger, a 4-stroke is going to be frustratingly slow.

If your dreams of a scooter are popping wheelings, zipping through traffic or carrying a buddy then a 2-stroke is really what you’re after. The Elite 80 is a neat scooter because it’s an example of a properly powered 4-stroke for scooting around town. I really wish legislation and insurance companies set their rules based on horsepower or top speed, rather than engine size so that manufacturers could create nicely powered 4-stroke scooters that appeal to the same crowd as 50cc’s.

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