In a turbocharger, the speed of the turbine and impeller is controlled by what mechanism?

• A. Throttle position
• B. Positioning of the waste gate
• C. Fuel-air mixture ratio
• D. Exhaust gas temperature

Answer: (B)

The main idea is that turbocharger speed is governed by a wastegate. The wastegate is a valve that can bypass some of the exhaust away from the turbine. When boost reaches the desired level, the wastegate opens, reducing the exhaust energy driving the turbine and keeping its speed (and the compressor’s speed) in check. When more boost is needed, the wastegate closes more, sending more exhaust through the turbine so it speeds up and increases boost. This direct control of exhaust flow to the turbine is how the system regulates turbine and impeller speeds. Throttle position, fuel-air mixture, and exhaust gas temperature influence engine performance and conditions, but they don’t actively regulate the turbine’s rotational speed.