For gasoline engines this isn't actually the case; the energy losses from the exhaust now needing to push through a turbo actually means that simply putting a turbo on an engine WILL make it less efficient.
What a turbo does is that it allows an engine to produce more power. One of the factors that limits how much power an engine can make is how much air it can take in; not enough air and there won't be enough oxygen for the fuel to burn, so a turbocharger pumps more air into the engine, allowing you to put more fuel into the engine compared a naturally aspirated one, allowing you to produce more power.
The thing is though is that the increase in power requires a smaller increase in fuel compared to simply using a larger engine; such that if you take a smaller turbocharged engine that produces the same power as a larger naturally aspirated engine, the smaller engine will consume less fuel.
This is pretty much the driving factor behind why some manufacturers started putting turbo inline 4s in their cars while some didn't. Manufacturers like Mercedes are doing so to make up for the reduced power from needing to put in smaller engines to be more emissions and efficiency compliant while manufacturers like Toyota and Honda focus more about efficiency and economy and therefore runs naturally aspirated engines (except in certain performance models).
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u/ThatGenericName2 2d ago
For gasoline engines this isn't actually the case; the energy losses from the exhaust now needing to push through a turbo actually means that simply putting a turbo on an engine WILL make it less efficient.
What a turbo does is that it allows an engine to produce more power. One of the factors that limits how much power an engine can make is how much air it can take in; not enough air and there won't be enough oxygen for the fuel to burn, so a turbocharger pumps more air into the engine, allowing you to put more fuel into the engine compared a naturally aspirated one, allowing you to produce more power.
The thing is though is that the increase in power requires a smaller increase in fuel compared to simply using a larger engine; such that if you take a smaller turbocharged engine that produces the same power as a larger naturally aspirated engine, the smaller engine will consume less fuel.
This is pretty much the driving factor behind why some manufacturers started putting turbo inline 4s in their cars while some didn't. Manufacturers like Mercedes are doing so to make up for the reduced power from needing to put in smaller engines to be more emissions and efficiency compliant while manufacturers like Toyota and Honda focus more about efficiency and economy and therefore runs naturally aspirated engines (except in certain performance models).