What is the purpose of valve overlap in an engine?

Valve overlap is a critical aspect of engine design that involves the period when both the intake and exhaust valves are open at the same time during the end of the exhaust stroke and the beginning of the intake stroke. This overlap serves several purposes, with enhancing power output being a primary advantage.

By allowing both valves to be open simultaneously, valve overlap facilitates the evacuation of exhaust gases and the intake of fresh air-fuel mixture more efficiently. This increased airflow can improve the overall volumetric efficiency of the engine, which translates to higher power output, especially at higher RPMs. As the engine draws in the fresh charge, the negative pressure generated by the exiting exhaust gases can help draw in the air-fuel mixture more effectively, optimizing combustion conditions.

The other options each focus on different benefits that may be associated with various aspects of engine performance, but the primary role of valve overlap in this context is to enhance the power output by improving the engine's breathing capabilities. This is particularly important in performance-oriented applications where maximizing horsepower and torque is crucial.