What effect does valve overlap have on an engine's efficiency?

Valve overlap occurs when both the intake and exhaust valves are open simultaneously for a brief period during the engine cycle. This design can significantly enhance an engine's performance and efficiency, particularly in terms of scavenging.

During the exhaust phase, the opening of the intake valve while the exhaust valve is still open allows fresh fuel-air mixture to enter the combustion chamber even as exhaust gases are being expelled. This overlap helps to create a more effective scavenging effect, where the incoming charge helps to push out the remaining exhaust gases. Efficient scavenging can result in a more complete combustion process, leading to improved engine performance, enhanced power output, and greater thermal efficiency.

By optimizing the mixture of air and fuel entering the combustion chamber, valve overlap can contribute to better combustion dynamics, particularly in high-performance engines. This increased efficiency can lead to improved throttle response and overall operational effectiveness, especially at higher RPMs.