What happens during the intake stroke of a gasoline engine?

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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.

During the intake stroke of a four-stroke cycle gasoline engine, the following process occurs:

Valve Position: The inlet valve opens to allow the entry of fuel and air.21
Piston Movement: The piston descends within the cylinder.21
Induction: This downward movement creates a partial vacuum, which draws an ignitable mixture of gasoline vapour and air into the cylinder.21

To optimize performance, the opening of the intake valve often occurs slightly before the piston reaches the top dead-centre position, and its closing is delayed until after the bottom dead-centre position. This timing utilizes the inertia of the gases to assist in filling the cylinder more effectively.3