What is boost pressure and its relation to engine performance in turbocharged engines?

• A. Boost reduces air density so engine runs cooler.
• B. Boost has no effect on engine power in a turbocharged engine.
• C. Boost increases intake air density, allowing more fuel and more power; controlled by wastegate/boost control.
• D. Boost is controlled by throttle position only.

Answer: (C)

Boost pressure in a turbocharged engine is the compressed air the turbocharger forces into the intake. This compression raises the air density in the cylinders, so more oxygen is available for combustion. With more oxygen, the engine can burn more fuel and produce more power. The boost level is kept in check by the wastegate and boost-control system, which open or close to limit how much exhaust energy drives the turbine and thus how much air is compressed. Intercoolers and electronic controls help manage temperature and precise boost levels. So, boost increases intake air density to enable more fuel and more power, and it’s controlled by the wastegate/boost-control system.