What term is used to describe the time frame during which the intake and exhaust valves are open?

• A. Valve Overlap
• B. Valve Timing
• C. Cam Phase
• D. Tappet Gap

Answer: (A)

Valve overlap describes the period in the engine cycle when both the intake and exhaust valves are open. This happens around the transition between exhaust and intake strokes, as the exhaust valve is closing and the intake valve is opening. The duration of this overlap is set by cam timing and can be adjusted with cam phasing in engines that use variable valve timing. Overlap influences scavenging—how effectively exhaust is pushed out and fresh mixture drawn in—and impacts idle quality and overall efficiency at different speeds. The other terms refer to broader timing concepts or separate mechanical clearances, not the specific window when both valves are simultaneously open.