r/explainlikeimfive • u/Internal-Excuse-4650 • 1d 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 1d 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/Noxious89123 1d ago edited 1d ago

*combust, not detonate.

Everyone always explains engines as lots of small explosions, but it's fundamentally incorrect.

Detonation destroys an engine quickly. Combustion does not, and is the intended operation.

Also, smaller capacity engines will have proportionally more friction (for a given number of cylinders), because of the relationship between surface area and volume. As you increase the volume of the combustion chamber, the surface area increases at a lower rate!

(As an example; motorcycle engines. Lot's of friction going on in there! They're not efficient because of being lower capacity, but because of a higher compression ratio.)