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Difference between Two and Four-Stroke Engines

Difference between Two and Four-Stroke Engines

When looking to purchase a new or used engine, it’s important to understand the difference between two and four-stroke engines. Two-stroke engines are cheaper and generate more power but they also produce more emissions. Four-stroke engines are more fuel-efficient and produce fewer emissions, but they also cost more. It’s important to decide which characteristics are most important to you before making a purchase.

What is Two Stroke-Engine?

  • A two-stroke engine is an internal combustion engine that completes a power cycle with two strokes (up and down movements) of the piston during only one crankshaft revolution. This is in contrast to a four-stroke engine, which uses four strokes of the piston to complete a power cycle during two crankshaft revolutions.
  • In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with fresh intake air being drawn into the simultaneously expelled exhaust gases.
  • Two-stroke engines often have a high power-to-weight ratio, power being available in a narrow range of rotational speeds called the “power band”. Compared to four-stroke engines, two-stroke engines have a greatly reduced number of moving parts, and so can be more compact and significantly lighter.
  • The first commercial two-stroke engine involving in-cylinder compression is attributed to Scottish engineer Dugald Clerk, who patented his design in 1881. However, unlike most later two-stroke engines, his had a separate charging cylinder.

What is Four Stroke-Engine?

A four-stroke engine is an internal combustion engine in which the piston completes four separate strokes while turning a crankshaft. Four-stroke engines are more powerful and efficient than two-stroke engines, but they are also more complex and expensive to build. Four-stroke engines are typically used in automobiles, motorcycles, and small aircraft. Two-stroke engines are still used in some lawn mowers and other small engines because they are lighter and cheaper to produce.

Difference between Two and Four-Stroke Engines

  • Two and four-stroke engines are the two most common types of engines used in internal combustion applications. Two-stroke engines are typically found in smaller applications such as lawnmowers and outboard motors, while four-stroke engines power everything from cars to large trucks. There are several key differences between these two types of engines. Two-stroke engines are typically lighter and more compact than four-stroke engines, making them ideal for portable applications.
  • Two-stroke engines also have a higher power-to-weight ratio, meaning they can generate more power per unit of weight. However, two-stroke engines tend to be less fuel-efficient and produce more emissions than their four-stroke counterparts. Four-stroke engines, on the other hand, are more efficient and powerful, but they are also larger and heavier. As a result, four-stroke engines are typically used in applications where size and weight are not major concerns.


In conclusion, there are several key differences between two and four-stroke engines. Understanding these differences can help you choose the right engine for your needs.

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