What effect does the throttle have on engine manifold pressure?

The throttle plays a crucial role in regulating engine manifold pressure, which is an important aspect of managing engine performance in a reciprocating aircraft engine. When the throttle is opened, it allows more air (and therefore fuel) into the engine, which increases the manifold pressure. Conversely, when the throttle is closed, there is a reduction in the airflow into the engine, leading to a decrease in manifold pressure.

Understanding this relationship is key for pilots as it directly impacts engine performance and efficiency, particularly during various phases of flight such as takeoff, climb, cruise, and descent. Proper management of the throttle can help achieve optimal performance while maintaining engine health.

In contrast, the other options fail to capture this important relationship accurately. For example, stating that the throttle decreases pressure when opened misrepresents its function. Saying it has no effect completely neglects the direct influence the throttle has on the engine's operating conditions. Lastly, claiming that it increases pressure when closed misinterprets how the throttle controls airflow into the engine and its resulting effect on manifold pressure.