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Difference
| Four Stroke Engine | Two Stroke Engine | |
| 1. | It has one power stroke for every two revolutions of the crankshaft. | It has one power stroke for each revolution of the crankshaft. |
| 2. | Heavy flywheel is required and engine runs unbalanced because turning moment on the crankshaft is not even due to one power stroke for every two revolutions of the crankshaft. | Lighter flywheel is required and engine runs balanced because turning moment is more even due to one power stroke for each revolution of the crankshaft. |
| 3. | Engine is heavy. Power to weight ratio is low | Engine is light. Power to weight ratio is high |
| 4. | Engine design is complicated due to valve mechanism. | Engine design is simple due to absence of valve mechanism. |
| 6. | Less mechanical efficiency due to more friction on many parts. More wear and tear. More maintenance is required | More mechanical efficiency due to less friction on a few parts. Less wear and tear. Less maintenance is required |
| 7. | More output due to full fresh charge intake and full burnt gases exhaust.
mep is high |
Less output due to mixing of fresh charge with the hot burnt gases.
mep is low |
| 8. | Power developed is less | Power developed is more (almost double) |
| 9. | Gear box [to reduce speed & reversing] is connected between engine and propeller shaft | Engine directly connected to propeller shaft. Engine is reversible |
| 10. | Engine consists of inlet and exhaust valve. | Engine consists of inlet port and exhaust port/valve. |
| 11. | More thermal efficiency. | Less thermal efficiency, as effective compression ratio is less |
| 12. | Separate cylinder L.O is not required | Separate cylinder L.O is required |
| 13. | High speed & Short Stroke – Costly fuel of better ignition quality should be used | Slow speed & Long Stroke – effective scavenging and cheap fuel of low ignition quality can be burnt |