2-Stroke Vs 4-Stroke Diesel Engines – What Is The Difference?

Last Updated on July 20, 2025 by Azim Uddin

Most modern vehicles use 4-stroke diesel engines. On the other hand, the use of 2-stroke engines has decreased quite a bit. However, what’s the difference between these two?

Here’s what you should know about 2-stroke vs 4-stroke diesel engines. The main difference is that the combustion cycle operates in a 2-stroke engine and a 4-stroke engine. This makes the 4-stroke engine more costly but durable. On the contrary, the 2-stroke engine is cheaper but not as durable.

Moving on, we will tell you all about the operating systems of these engines and their key differences. Additionally, we will give you the pros and cons of both engines to find out what suits you best. So, keep reading! 

Difference Between 2-Stroke And 4-Stroke Diesel Engines: How They Work

To understand the difference between 2-stroke and 4-stroke diesel engines, we need to understand the way they operate. Check their working principles below.

2-stroke Diesel Engine

• In a 2-stroke diesel engine, the first stroke includes compression and ignition strokes of a combustion cycle. This is an upward stroke of the piston, which compresses an air-fuel mixture into the crankcase. Consequently, the air-fuel mixture is ignited by the spark plugs.
• The second stroke consists of exhaust and ignition strokes. Now, a downward stroke of the piston, forced by the ignition, unveils the exhaust port. This releases the toxic gasses burnt due to combustion. Simultaneously, it allows the entry of fresh air-fuel mixture through the inlet port.
• These engines don’t need valves to allow the entry or exit of gasses through the port. The movement of the piston is adequate to fulfill the needs of a valve.
• Thus, the combustion cycle is completed through two strokes of the piston or one revolution of the crankshaft. 

4-stroke Diesel Engine

• As mentioned previously, a 4-stroke engine has four strokes. The combustion cycle starts with the intake stroke that pushes down the piston. This opens the inlet valve, creating a vacuum in the cylinder. So, the air is sucked into the cylinder, during which fuel mixes with it, creating an air-fuel mixture ratio.
• Then, the compression stroke follows where the piston moves up, and the valve closes, sealing the air-fuel mixture in the cylinder. Here, the air-fuel mixture is compressed, which prepares it for the ignition stroke.
• In the ignition stroke, the spark plug ignites the mixture rapidly. This creates a high pressure forcing down the piston. Once the piston is down, the exhaust stroke starts.
• The exhaust stroke is the fourth and final stroke, where the exhaust valve opens, and the piston moves up. This releases the burnt gasses through the open valve. This completes the combustion cycle of a 4-stroke diesel engine, which consists of 2 revolutions of the crankshaft.

Key Differences Between 2-Stroke And 4-Stroke Diesel Engines

Now you know the difference between the operations of these engines. For a better understanding, we’ve summarized some key differences in the table.

2-Stroke Diesel Engine	4-Stroke Diesel Engine
Two strokes of the piston.	Four strokes of the piston.
One revolution of the crankshaft to complete the cycle.	Two revolutions of the crankshaft to complete the cycle.
Works with inlet and exhaust ports.	Works with valves.
Compression stroke occurs through both sides of the piston.	Compression occurs through the top of the piston.
Higher torque at higher RPM.	Higher torque at lower RPM.
The crankcase is airtight.	The crankcase isn’t airtight.
Lightweight and easy to manufacture.	Heavyweight equipment and hard to manufacture.
Higher horsepower output.	Lower horsepower output.
More power generation.	Less power generation.
Low thermal efficiency.	High thermal efficiency.
Requires more lubrication from the engine oil to prevent wear and tear of the engine.	Requires less lubrication from the engine oil to prevent wear and tear of the engine.
Used in smaller, lightweight applications like scooters, motorcycles, jet skis, etc.	Used in bigger, heavyweight applications like cars, trucks, modern bikes, etc.

FAQ

For in-depth knowledge about 2-stroke vs 4-stroke diesel engines, everything we’ve discussed so far should suffice. However, let’s answer some frequently asked questions for your convenience.

Q. Why are 2-stroke diesels so loud?

The exhaust port creates a loud noise when releasing the combustion byproducts. Also, the engine contributes to resonances, increasing the noise.

Q. Can you turn a 2-stroke into a 4-stroke?

While this might be theoretically possible, we don’t recommend it. Doing so would require complicated modifications by an expert.

Conclusion

Most drivers don’t know the difference between 2-stroke vs 4-stroke diesel engines despite having used them both. The key difference is their operation. The combustion needs two strokes for a 2-stroke engine, and four strokes for a 4-stroke.

4-stroke engines have more complex designs and valve mechanisms. While this increases their cost, they provide excellent services in the long run. 2-stroke engines, however, have a simpler, lightweight design. They aren’t as durable but cost significantly less.