system
Given the following post, respond as if you're commenting on Reddit:
human
Is it true that putting a turbo on a car can make it achieve better fuel efficiency. If so how does this happen and if not how does it not happen?
gpt
Simply put, a turbo charger uses the exhaust air energy to compress the intake air.  What this does is provide more oxygen in a unit volume.  When this compressed air is put into a cylinder, more fuel can thus be added to combust with all the extra oxygen. This allows for more power and more energy per piston cycle.

Adding boost to an engine uses energy.

The reason turbos are even more efficient is because when you *don't* need extra power, then the engine runs on *low* boost, in such a way that it uses gasoline more efficiently than naturally aspirated (non turboed) engines.

Mathematically, turbo charging an engine has zero downsides for efficiency. A properly tuned turbo will always increase efficiency.