In modern vehicles, turbochargers are typically controlled by the engine computer which constantly adjusts boost pressure based on the engine load and speed to balance power and fuel economy. When the engine is under a light load, like when cruising on the highway, the turbocharger can be used to increase air flow without substantially increasing fuel consumption. In this scenario, the turbocharger can indeed decrease fuel consumption compared to a naturally aspirated engine.
On the other hand, when the engine is under a heavy load, like during acceleration or towing a heavy trailer, the turbocharger boosts the air flow and fuel consumption increases accordingly. In these scenarios, the fuel efficiency will be lower compared to a naturally aspirated engine.
