As rotational speed increases in a four-stroke engine, what happens to the valve overlap?

In a four-stroke engine, valve overlap refers to the period when both the intake and exhaust valves are open simultaneously, allowing for the efficient expulsion of exhaust gases and the intake of fresh air-fuel mixture. This phenomenon is crucial for optimizing engine performance, especially at higher speeds.

As rotational speed increases, the camshaft's design, which dictates the timing and duration of valve events, typically keeps the valve overlap relatively constant across a wide range of engine speeds. This is primarily due to the engine's tuning and the goal of maintaining a balance between exhaust gas evacuation and intake flow.

At higher rotational speeds, the engine requires precise timing to ensure that there is adequate time for the intake valve to open and close in relation to the exhaust valve. If the valve overlap were to increase or decrease significantly with speed, it could compromise engine efficiency and power output. Therefore, a constant valve overlap ensures reliable and effective performance across a range of operating conditions.

In summary, as the rotational speed of a four-stroke engine increases, the valve overlap typically remains constant to maintain optimal engine performance and efficiency.