Britannica Sources used in this answer

Which four strokes occur in a four-stroke gasoline engine cycle?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Labeled cross-sectional diagram of a V-type gasoline engine for an automobile, showing internal components such as pistons, crankshaft, camshaft, intake and exhaust valves, connecting rods, spark plugs, and intake manifold. — gasoline engine Cross section of a V-type engine.

The four-stroke cycle is a fundamental process in internal-combustion engines that requires four distinct movements of the piston to complete one cycle. These strokes are:1

Intake stroke: The piston descends with the inlet valve open, drawing an ignitable mixture of gasoline vapor and air into the cylinder.1
Compression stroke: The piston ascends with both valves closed, compressing the fuel mixture before ignition.12
Power stroke: Following ignition by an electric spark, the expanding gases press against the piston head, driving it downward with both valves remaining closed.1
Exhaust stroke: The piston ascends again, forcing the spent combustion products out through the open exhaust valve.13

This cycle repeats continuously, with each full sequence requiring two complete revolutions of the crankshaft.1