Which method is effective in improving volumetric efficiency?

Increasing valve overlap is an effective method for improving volumetric efficiency in an internal combustion engine. Volumetric efficiency refers to the engine's ability to fill its cylinders with air and fuel during the intake stroke. By allowing the intake and exhaust valves to overlap, some exhaust gases can exit the cylinder while the intake valve opens. This process maintains a more favorable pressure difference, which helps draw in a more considerable amount of fresh air and fuel mixture into the combustion chamber.

Additionally, the presence of this overlap ensures better scavenging of exhaust gases, reducing residual gases in the cylinder. Consequently, this promotes a higher intake of the air-fuel mixture on the subsequent cycle, leading to improved volumetric efficiency and enhancing overall engine performance.