What happens to the pressure in the induction manifold of a normally aspirated engine as the throttle is opened?

In a normally aspirated engine, the induction manifold pressure is directly related to the throttle position. As the throttle opens, the flow of air into the engine increases, which leads to an increase in the pressure within the induction manifold.

When the throttle is fully closed, there is a high pressure drop across the throttle plate due to the restricted airflow, resulting in lower manifold pressure. As the throttle opens, the restriction diminishes, allowing more air to flow into the manifold and subsequently increasing the pressure. This relationship between throttle position and manifold pressure is critical for engine performance, as it affects the amount of fuel that can be introduced into the combustion chamber, thus influencing the overall power output of the engine.

It is important to note that in scenarios where the throttle is partially open or near the wide-open position, the relationship between air velocity and manifold pressure may exhibit some complexities, but the overall trend is an increase in manifold pressure as the throttle opens. Therefore, the correct answer reflects this fundamental principle of engine operation.