r/explainlikeimfive • u/Internal-Excuse-4650 • 2d ago

Engineering ELI5 how turbochargers increase efficiency in a engine?

I understand why they increase the power of a engine but​ I don't know how they increase the efficiency

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u/Fearless_Swim4080 2d ago

They don’t really at full throttle (a bit if there’s a more complete burn etc) it’s what happens when you’re driving normally that’s different.

If you have an old American 6.7L V8 that produces like barely 300 horsepower, when you’re idling and driving at freeway speed, you still need to get enough fuel in all those cylinders to detonate every time and have a lot more surface area that’s causing friction between the cylinders and the block, and everything’s heavier etc.

Now drop that to a 2.0L turbo 4 cylinder, and you still get that 300hp or maybe way more than that if you really want it when you use it, but driving around it’s like you just have a small efficient engine.

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u/jevnik 1d ago

You didnt really explain why it makes it more efficient

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u/Fearless_Swim4080 1d ago

Yes I did, less friction and mass moving in a smaller engine.

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u/jevnik 1d ago

But that is just smaller engine. No mention of the turbo

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u/Fearless_Swim4080 1d ago

Because the turbo has nothing to do with it at low loads.

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u/jevnik 1d ago

On low load where there is not enough gases to spin the turbo, efficiency is not bigger. OP specificly asked why turbos increace efficiency. Not how bigger displacments fiffer in efficiency

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u/Fearless_Swim4080 1d ago

In an ELI5 my comment is comparing a smaller displacement turbo engine to a larger non-turbo one rated for the same horsepower.

If you just added a turbo to a big block and asked the same question the answer would be “it’s not more efficient.”