Difference Between a 2-Stroke and a 4-Stroke
The Difference between a 2-stroke and a 4-stroke engine is how quickly this combustion cycle process occurs, based on the number of times the piston moves up and down during each cycle.
In a 4-stroke engine, the piston completes 2-strokes during each revolution: one compression stroke and one exhaust stroke, each being followed by a return stroke. The spark plugs fire only once every other revolution, and power is produced every 4-strokes of the piston. These engines also do not require pre-mixing of fuel and oil, as they have a separate compartment for the oil.
In a 2-stroke engine, the entire combustion cycle is completed with just one piston stroke: a compression stroke followed by the explosion of the compressed fuel. During the return stroke, the exhaust is let out and a fresh fuel mixture enters the cylinder. The spark plugs fire once every single revolution, and power is produced once every 2-strokes of the piston. Two-stroke engines also require the oil to be pre-mixed in with the fuel.
Pro’s and Con’s:
So, which is ‘better’? Here are a few of the pro’s and con’s to both engine designs:
- As far as efficiency goes, the 4-stroke certainly wins. This is due to the fact that fuel is consumed once every 4 strokes.
- Four-stroke engines are heavier; they weigh upwards of 50% more than a comparable 2stroke engine.
- Typically, a 2-stroke engine creates more torque at a higher RPM, while a 4-stroke engine creates a higher torque at a lower RPM.
- The 4-stroke engine is also much quieter, a 2-stoke engine is significantly louder and has a distinctive, high-pitched “buzzing” sound.
- Because 2-stroke engines are designed to run at a higher RPM, they also tend to wear out faster; a 4-stroke engine is generally more durable. That being said, 2-stroke engines are more powerful.
- Two-stroke engines are a much simpler design, making them easier to fix. They do not have valves, but rather ports. Four-stroke engines have more parts, therefore they are more expensive and repairs cost more.
- Two-stroke engines require pre-mixing of oil and fuel, while the 4-strokes do not.
- Four-strokes are more environmentally friendly; in a 2-stroke engine, burnt oil is also released into the air with the exhaust.
Two-stroke engines are typically found in smaller applications such as remote-controlled cars, lawn tools, chainsaws, boat motors and dirt bikes. Four-stroke engines are found in anything from go-karts, lawnmowers and dirt bikes, right up to the typical internal combustion engine in your vehicle. It’s up to you to decide which engine you prefer, and for what purpose.