To maintain the Rated Boost of a supercharged engine while reducing the R.P.M., what must be done to the throttle valve?

To maintain the Rated Boost of a supercharged engine while reducing the R.P.M., it is necessary to open the throttle valve. When the engine's speed decreases, the airflow through the engine also reduces, which can lead to a drop in boost pressure generated by the supercharger. By opening the throttle valve, you increase the amount of airflow into the engine, compensating for the decrease in R.P.M. This adjustment ensures that the engine continues to receive sufficient air, allowing the supercharger to maintain the desired boost levels.

If the throttle valve were to be closed, it would limit airflow into the engine, thereby reducing the boost pressure instead of maintaining it. Similarly, adjusting components like the waste gate, which controls exhaust flow to the turbocharger in turbocharged systems (not applicable directly to supercharged systems), would not directly address the need for increased airflow at reduced engine speeds.