What occurs during valve overlap?

During valve overlap, both the intake and exhaust valves are open simultaneously for a brief period during the engine's four-stroke cycle. This phase typically occurs at the end of the exhaust stroke and the beginning of the intake stroke. By having both valves open, the outgoing exhaust gases can help draw in fresh air-fuel mixture into the combustion chamber, enhancing the engine's efficiency and performance.

Valve overlap is beneficial because it allows for better scavenging of exhaust gases, which helps to ensure a more complete intake of fresh air and fuel into the cylinder. This overlapping of the timing of the valves is particularly important in high-performance engines, as it can lead to increased power output and improved overall engine responsiveness. Understanding valve overlap is essential for optimizing engine timing and tuning in small engine applications.