When should the combustion process be completed if the fuel/air ratio is proper and ignition timing is correct?

The combustion process should be completed just after top center at the beginning of the power stroke in a properly functioning engine with the correct fuel/air ratio and ignition timing. At this point in the cycle, the piston has reached its highest position, and the mixture of fuel and air has been ignited. Ideally, maximum pressure from the combustion should occur just after top dead center (TDC), which allows the force from the expanding gases to push the piston down effectively during the power stroke.

Completing combustion at this point ensures that the engine produces maximum power and efficiency. If combustion were to finish too early or too late, it would reduce the engine's effectiveness, leading to a decrease in power output and potentially increasing engine wear or emissions.

Aiming for combustion to occur just after TDC is crucial for maintaining the engine's operational efficiency and optimizing performance.