In the four-stroke internal combustion engine, hot vapors are expelled during the stroke.

In the four-stroke internal combustion engine, hot vapors are expelled during the exhaust stroke.

A four-stroke cycle engine is an internal combustion engine that uses four distinct piston strokes (intake, compression, power, and exhaust) to complete one operating cycle.  The piston make two complete passes in the cylinder in order to complete one operating cycle.

The four separate strokes are; intake, compression, combustion and exhaust.

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