Will a turbocharger help fuel economy?

Answer 1

"Nope, a turbocharger forces more air into your engine and the more air you have the more fuel you'll need to prevent a lean mixture."

It could, but at present it doesn't. American car manufacturers add them to increase horsepower only. By increasing the amount of air and fuel stuffed into an engine, you increase the compression ratio over that which it was before turbocharging on an otherwise unmodified engine. IF you increase the octane of the gasoline so you don't get detonation, you will get more power in each cycle. BUT, the amount of power taken to compress the increased amount of mixture is larger in each cycle, so it isn't free.

IF, however, the engine was modified to lower the compression ratio before the turbocharger was added and the amount of turbocharger boost raised the compression ratio to the normal rate, then possibly you would get some increase in fuel economy as the amount of work done by the engine crankshaft to compress the mixture would decrease. However, this has not been done yet (as far as I know).

It is also possible that theoretically a smaller engine could be used in a vehicle because the turbocharged engine can produce the same horsepower with a smaller engine. In such case there would be weight reductions but the advantage here would be minor.

Turbochargers are definitely better than superchargers for economy purposes as the energy used for compression comes from waste heat and exhaust expansion rather than parasitic energy taken from the crankshaft.

For industrial diesel applications, turbocharging is done regularly for purposes of economy.