Which statement describes the overall effect of a larger exhaust pipe diameter on engine performance?

• A. It can improve intake airflow.
• B. It will always reduce performance.
• C. It has no effect on any aspect of performance.
• D. It will always increase fuel consumption.

Answer: (A)

A larger exhaust pipe diameter reduces resistance for exhaust gases, lowering backpressure. With less backpressure, exhaust pulses clear more efficiently, which improves scavenging—the process that helps vacuum form in the intake and pulls air into the cylinder. That means the engine can breathe easier on the intake stroke, often boosting overall airflow into the engine and, in many conditions, performance. The idea isn’t that bigger is always better in every situation—extremely large diameters can hurt low-end breathing and aren’t a universal guarantee of better fuel economy—but the best-supported effect is that, by reducing backpressure, the engine can draw in air more readily, hence improved intake airflow.