Generator Basics: 2-Stroke vs. 4-Stroke

2-Stroke vs. 4-Stroke

Most modern medium size generator engines are “4-stroke” or four-cycle engines, as opposed to “2-stroke” or two-cycle engines that are heavily favored in very large and Marine-use applications. Despite the widely accepted use of 4-stroke generator engines, it important to know the difference. This article will cover the basics of 2-stroke vs. 4-stroke.

What is a stroke?

Wikipedia defines an engine “stroke” as follows: “A phase of the engine’s cycle, during which the piston travels from top to bottom or vice-versa.”


A two-stroke engine completes a power cycle with two strokes of the piston during only one crankshaft revolution. The end of the combustion stroke and the beginning of the compression stroke happen at the same time in a 2-stroke engine, with the intake and exhaust functions happening simultaneously as well.

More efficient and powerful than its 4-stroke counterpart, it also runs hotter and components wear down quicker.

The larger maritime engines that still rely on the powerful 2-stroke to move their monolithic loads have been heavily fortified to combat the intense heat and friction and can last decades without failure.

Another downside is the spent exhaust from the 2-stroke engine is much more “dirty” than the 4-stroke, making them less than ideal in highly regulated emissions environments.

Though rare in generator sets these days, you can still come across excellent 2-stroke engines like the popular Detroit Diesel model 71 and the 92.

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4-stroke engines have become the standard in power generation due mostly to how much cleaner they run then the 2-stroke engines. Separating the intake from the exhaust stroke reduces the amount of unburnt fuel and expanding gases released through the exhaust system. It also reduces the overall operating temperature, decreasing the wear and tear on engine components.

In the 4-stroke engine, the piston completes four separate strokes while turning the crankshaft:

  1. Intake
  2. Compression
  3. Combustion
  4. Exhaust

The downside is the extra strokes reduce the available power significantly. A 2-stroke engine produces power on each revolution, whereas the 4-stroke produces power on every other revolution. This reduces the efficiency of the engine in exchange for more manageable emissions and longer life.

Of course, this is just a basic introduction to the 2-stroke vs. 4-stroke conversation. For more information please give us a call at 610-658-3242.

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What is a 2-stroke engine?

What is the difference between 2 stroke and 4 stroke engines?

2-stroke vs. 4-stroke

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