The turbocharger turbine creates a ______ pressure in the exhaust system which leads to a ______ in overall efficiency.

• A. back pressure; reduction
• B. low pressure; increase
• C. no change; neutral
• D. positive pressure; improvement

Answer: (A)

When exhaust gas drives the turbine, energy is taken from the gas stream to turn the compressor. That introduces a restriction in the exhaust path, so the pressure builds up upstream of the turbine. This is exhaust back pressure. That back pressure makes the engine work harder to push exhaust out during the exhaust stroke, increasing pumping losses and lowering efficiency. So the turbine creates back pressure in the exhaust system, which leads to a reduction in overall efficiency. The other options don’t fit because they imply lower or unchanged exhaust pressure or a gain in efficiency, which isn’t the real effect of the turbine’s restriction on the exhaust flow.