The four stroke cycle is the basic principle of operation of the internal combustion engines used in road cars.

The complete combustion process takes four movements or strokes of the piston, and two revolutions of the crankshaft.

The cycle begins with the piston at top dead centre. The piston then descends on the induction stroke, sucking air or an air/fuel mixture (depending on the type of engine) into the cylinder. The piston then rises, compressing the mixture, the mixture ignites and the piston is driven down on the power stroke. Finally the piston rises again on the exhaust stroke, expelling the burnt gases from the combustion chamber.

Compare two stroke cycle.