What effect does valve overlap have on the cylinder pressure?

Valve overlap refers to the period during the engine cycle when both the intake and exhaust valves are open simultaneously. This design feature is intentional in many engine types, as it allows for improved performance during specific phases of the engine cycle.

When both valves are open, the exhaust gases are flowing out of the combustion chamber while the fresh air-fuel mixture is being drawn in. This flow of exhaust gases can create a dynamic effect that reduces pressure within the cylinder. As the exhaust is exiting the cylinder, it can facilitate a lower pressure environment, which helps to draw in more fresh mixture through the intake valve. This phenomenon, often referred to as "scavenging," improves the overall efficiency of the engine by enhancing volumetric efficiency and ensuring a better charge is delivered for combustion.

Understanding the implications of valve overlap is crucial for tuning engine performance, as optimizing this overlap can lead to increased power output and better engine response. The other choices do not directly relate to the fundamental effects of valve overlap on cylinder pressure, which is why they do not convey the same relevance in this context.