At what point is a spark timed to ignite the mixture of petrol and air?

The spark is timed to ignite the mixture of petrol and air at the top of the stroke, which corresponds to the point where the piston reaches the top of its compression stroke, also known as Top Dead Center (TDC). At this moment, the air-fuel mixture is fully compressed, leading to optimal conditions for combustion. Igniting the mixture at this point ensures that the explosion occurs just as the piston begins its downward stroke, maximizing power and efficiency.

This timing is crucial because an early or late ignition can lead to knocking or engine performance issues. By igniting at the top of the stroke, the engine can extract maximum energy from the combustion process, improving overall vehicle performance.