2 Stroke vs 4 Stroke Engine : 7 Difference Between Two Stroke and Four Stroke Engine

Througout the history of automotive engine, you had learn about 2 stroke, 4 sroke, petrol engine, and diesel engine. If we talk about petrol and diesel engine, obviously they have different fuel.

But how about two stroke and four stroke ?

Evidently, both diesel and petrol engine have 2 stroke and 4 stroke type. So what is the difference between both of them ? wich one is better ?

Today, we will learn all the difference between 2 stroke engine and 4 stroke engine.

Difference Between 2 Stroke and 4 Stroke Engine

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From all of the difference, there are 7  main difference ;

1. Working cycle

Both of these engines have different working principles. The two stroke engine only has 2 steps in one work cycle where each step requires half a crank rotation. So the principle of a two-stroke engine is producing combustion each crankshaft rotation (I cycle = 1 crank rotation)

For more details; Understanding the 2-stroke engine works principle

While the 4 stroke engine has four work steps in one cycle where each step also requires half a crank rotation. So that the working principle of the 4 stroke engine is producing combustion in two crankshaft rotation (1 cycle = 2 crank rotation).

Further more you can check this, 4 stroke engine diagram and working process

Nevertheless, both 2-stroke and 4-stroke have same working proccess (intake-compression-combustion-exhaust). In two stroke, there are 2 process in one step. While 4 stroke have one process each step.

2. Difference in output power

As explained above, 2 stroke engine producing combustion in every crankshaft rotation. So, for example if engine work in 1,000 RPM, it will occur 1,000 times combustion in one minute.

While the 4 stroke engine, only produces combustion every two crank rotation. So that for example if the engine rotates at 1,000 RPM, there will only be 500 burning times in one minute.

Here we can see the amount of combustion in 2 stroke engine is twice more than the 4 stroke engine even though the same RPM. This cases, make 2 stroke engine more powerfull than 4 stroke engine.

3. Differences in emissions issued

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Emission is the content of engine combustion residual gas, even though 2 stroke engine has larger power but the output power ratio is not twice as large as the 4 stroke engine. That's due to the combustion process in 2 stroke engine doesn't work effectively.

So that the emissions also still contain gasoline, this can certainly make the emission worse than the 4 stroke engine.

While on a 4 stroke engine, the steps are run regularly without overlapping. It make the combustion process take place more perfectly. So even though the amount of combustion is not as intense as the 2 stroke engine, but the power is still quite good and the emissions produced are only in the form of CO without containing gasoline.

4. Engine oil consumption

In a two stroke engine, we know side oil. This side oil is basically the same as other types of engine oil, but here the side oil will run out if the engine continues to turn on. The reason is because this oil is used to lubricate the movement of the piston through the combustion chamber. So, this oil has the potential to burn in the combustion chamber. That is why, the two stroke motorcycles release white smoke and the emissions are also worse.

For 4 stroke engines, it does not require lubricating side oil due to piston lubrication and all engine components will be supported by engine oil that is accommodated in the crankcase. Construction on four stroke engine does not allow oil to enter the combustion chamber. So, it can be said that a normal 4-stroke engine has a 0 liter oil consumption.

5. Engine construction

In terms of construction, 2 stroke engine has a very simple form and construction. This engine only consists of a cylinder block, cylinder head, piston & connecting rod, crankshaft, without a valve mechanism and timming chain.

While on a 4 stroke engine, it will be more complicated because there is a valve mechanism driven by a crankshaft through a chain.

6. Fuel consumption

As we discussed in the second point, that the two stroke engine produce 1,000 times combustion every minute if the engine speed is 1,000 RPM while the 4 stroke engine, with the same speed only produces 500 fires every minute.

Here we can see that the 2 stroke engine has higer fuel consumption than the other one. The fuel consumption is two times higher than the 4 stroke engine.

7. vibration fluctuations

Engine vibration fluctuations occur due to imbalances in combustion. In 2 stroke engines, vibration fluctuations should be very small because there is combustion in every crankshaft rotation. So the rotation is more stable.

While on four stroke engines is not so, because the combustion occurs every 2 crank rotation, there will be a large vibration fluctuations because there is not every crank rotation to get the power boost from combustion.

That is why, the RPM of 4 stroke motorbikes is less stable in idle speed (can be felt from the sound).

Except for 4-cylinder engines, 4-cylinder engines have low vibration fluctuations because the combustion of each cylinder will be different. The combustion will occur in each step, in other words, in two crank turns, 4 fires occur at the same interval. So the engine load becomes smoother.

So, the conclucion

If you ask wich one is better, we ca answer that four stroke engine is better on every side except in power. In nowdays, fuel economic vehicle is more needed than powerfull vehicle. More over, there are regulations that regulate engine emission. It make 2 stroke engine hard to pass, because this engine has worshe emissions.

Thank you, hope usefull for all of you.