What effect does a restricted exhaust have on engine RPM?

A restricted exhaust system can significantly impact engine performance, particularly in terms of RPM. When exhaust flow is obstructed, engine efficiency is compromised. The exhaust gases cannot exit the engine smoothly, which leads to increased backpressure. This backpressure can cause the engine to struggle with expelling gases, ultimately reducing its ability to draw in fresh air and fuel for the next combustion cycle.

The correct choice indicates that the restriction typically limits the engine RPM well below 6000 RPM. This is particularly relevant because engines are designed to operate optimally within certain RPM ranges, and a significant restriction can hinder performance by reducing the maximum attainable RPMs. For high-performance engines, achieving RPMs over 6000 is often crucial. If the exhaust is restricted, it restricts the engine's ability to maintain higher RPMs, thus impacting overall power and torque as well.

In contrast, suggesting limits higher than 6000 RPM wouldn’t accurately reflect the typical performance impact of exhaust restrictions because most engines, especially performance-oriented models, start to experience notable performance degradation due to backpressure well below that threshold. Additionally, a restriction affecting 'any RPM' implies that even at low RPMs the effect would be equally pronounced, which isn’t the case since lower RPMs are less