What is the piston's position during overlap?

During overlap in an internal combustion engine, both the intake and exhaust valves are open simultaneously, allowing for the exhaust gases to exit while the intake air is drawn in. This typically occurs around the point when the piston is at the top of its stroke, referred to as top dead center (TDC).

At this position, the piston is ready to transition from the exhaust phase into the intake phase. When the intake valve opens and the exhaust valve is still closing, the piston is essentially sitting at TDC, where the cylinder volume is at its minimum and pressure is at its peak for the exhaust stroke.

Understanding the piston’s position during overlap is critical for optimizing engine performance, as it influences the timing and efficiency of the intake and exhaust processes. This is particularly important because an ideal overlap period can enhance the charge filling of the cylinder and improve overall engine efficiency.