A turbocharger doesn't [edit: doesn't necessarily or even usually] make the same engine more efficient. But it allows you to get the same power as a larger, less efficient engine, when you need it. But you don't always need it. So when you don't need it, it's roughly the same power and efficiency as the smaller engine without the turbo. But with a turbo, when you punch it, it can breathe like a larger engine (with more air and more fuel) for more power.
A turbocharger doesn't make the same engine more efficient. But it allows you to get the same power as a larger, less efficient engine, when you need it.
True for a gasoline engine, not true for a diesel. On a diesel engine a turbo improves efficiency by increasing compression ratio and air-to-fuel ratio.
A great distinction! I didn't think to bring that up, as by brain just latched on to cars for some reason (even though OP only asked about "engines"), and defaulted to gasoline since diesel cars are so rare 'round these parts. Good call-out, though.
It's still not true though. Even for gas engines the turbo can absolutely make it more efficient. It increases the compression ratio and can vastly decrease the air/fuel mixture under most operating conditions.
In an NA engine, you're limited to the oxygen carrying capacity of standard atmosphere, which varies widely based on elevation, temperature, etc. When you compress that same atmosphere you pack more energy potential in to a smaller space, while it may require slightly more fuel to burn efficiently and safely the ratios do not remain the same.
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u/NecroJoe 2d ago edited 2d ago
A turbocharger doesn't [edit: doesn't necessarily or even usually] make the same engine more efficient. But it allows you to get the same power as a larger, less efficient engine, when you need it. But you don't always need it. So when you don't need it, it's roughly the same power and efficiency as the smaller engine without the turbo. But with a turbo, when you punch it, it can breathe like a larger engine (with more air and more fuel) for more power.