The key difference between two-stroke and four-stroke is that a 4-stroke engine completes one power stroke in four stages, which corresponds to two full revolutions of its crankshaft, whereas a 2-stroke engine accomplishes a power stroke in two stages, equivalent to one complete revolution of its crankshaft.
What is Two Stroke?
In a 2-stroke engine, the entire combustion process occurs within a single piston stroke. This includes compression, ignition of the compressed fuel, exhaust expulsion during the return stroke, and intake of a fresh fuel-air mixture.
The spark plugs ignite once per revolution, generating power every two piston strokes. Additionally, 2-stroke engines necessitate mixing oil with the fuel in advance.
What is Four Stroke?
In a 4-stroke engine, the piston performs two strokes in a single revolution: a compression stroke and an exhaust stroke, followed by a return stroke.
The spark plugs ignite the fuel-air mixture once every two revolutions, resulting in power generation occurring every four piston strokes. These engines have a dedicated oil compartment, eliminating the need for mixing fuel and oil beforehand.
Two Stroke Vs Four Stroke
The primary difference between two stroke and four stroke is given below:
| Aspect | Two Strokes | Four Strokes |
| Crankshaft Revolutions per Power Stroke | One | Two |
| Torque Generation | High | Less |
| Fuel Inlet/Outlet | Port | Valves |
| Thermal Efficiency | Lesser | Higher |
| Power-to-Weight Ratio | Larger | Lesser |
| Smoke Generation and Efficiency | More smoke, less efficiency | Less smoke, more efficiency |
| Lubricating Oil Requirement | More | Less |
| Wear and Tear | More due to poor lubrication | Less |
| Manufacturing Cost | Cheaper and simpler | Expensive due to lubrication and valves |
| Weight and Noise | Lighter and noisier | Heavier with a heavy flywheel, less noisy |