What is valve overlap in an engine?

Valve overlap is a critical phase in the operation of an internal combustion engine, particularly in the context of its timing and how it affects engine performance. When both the intake and exhaust valves are open simultaneously, this period is referred to as valve overlap.

During valve overlap, the exhaust gases are being expelled from the combustion chamber while fresh air-fuel mixture begins to enter. This can enhance engine efficiency by allowing for better scavenging of exhaust gases, as the incoming mixture helps push out the remaining exhaust. Furthermore, this overlap can lead to improved performance, especially at high RPMs, as it helps maintain smoother airflow through the engine.

Understanding valve overlap is essential for tuning an engine, as it influences power output, emissions, and overall engine responsiveness. The presence of this overlap can vary depending on the engine design, camshaft profile, and intended application.