Is turbocharging active when the waste gate is fully open?

• A. No
• B. Yes
• C. Sometimes
• D. Only at altitude

Answer: (A)

When the turbocharger is boosting, the exhaust energy spins a turbine that drives a compressor to raise intake air pressure. The wastegate acts as a control valve that dumps some of that exhaust away from the turbine to limit boost. If the wastegate is fully open, nearly all exhaust bypasses the turbine, so the turbine doesn’t receive enough energy to spin fast enough to increase the compressor output. As a result, the intake manifold pressure stays essentially at ambient, and the turbocharger isn’t actively boosting. The turbine might still turn a little from exhaust flow, but it doesn’t provide meaningful compression.

That’s why “No” is the best answer. The other options imply boosting under conditions where the wastegate has opened and can’t supply boost, or rely on altitude in a way that isn’t applicable to the control of boost in this scenario.