WonderLab X
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Four-stroke Engine

Turn the crankshaft and discover how the piston, connecting rod and valves work through a complete four-stroke cycle.

FIG. 001 Four-stroke engine · section
OTTO / 01
Playing
Piston motion → crankshaft rotationPower · 405°
405° / 720°
0°180°360°540°720°
Color indicates the gas phase. Teaching section with idealized valve timing.

How a four-stroke engine works

Follow the piston and valves through 720° of crankshaft rotation. Compare valve states at the same time as piston direction, then drag the angle control to inspect the transitions.

  1. Intake

    0–180°: The piston moves down and the intake valve opens, allowing fresh mixture into the cylinder.

  2. Compression

    180–360°: Both valves close. The rising piston compresses the mixture into the combustion chamber.

  3. Power

    360–540°: Ignition near top dead center is followed by expansion. The piston transmits motion through the connecting rod to the crankshaft.

  4. Exhaust

    540–720°: The exhaust valve opens and the rising piston expels exhaust gas.

Model assumptions and sources
  • The model uses a 76 mm bore, 60 mm stroke, 100 mm connecting rod and 9:1 geometric compression ratio.
  • Valve timing is idealized at the stroke boundaries. Combustion pressure, heat transfer and real valve mechanisms are not simulated.