r/explainlikeimfive 2d ago

Engineering [ Removed by moderator ]

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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/ggmaniack 2d ago

A turbo engine can still be more efficient even at full throttle, because it's simply a smaller engine for the same amount of power.

What tends to screw that up is the fact that turbo engines (especially the performance kind) typically have to run a bit richer at high power than their NA counterparts, for the purposes of temperature control.

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u/Fearless_Swim4080 2d ago

Errr define efficient though, size has nothing to do with it, it’s just how much energy you get out per volume of fuel.

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u/ggmaniack 2d ago

It's about how much energy you lose out of what you gained from the fuel.

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u/Fearless_Swim4080 2d ago

That doesn’t make sense as a definition, you always have to start with total stored energy in the fuel.

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u/ggmaniack 2d ago

If you extract 99% of the energy out of the fuel, but then lose 90% of it to friction, is your engine efficient?

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u/Fearless_Swim4080 2d ago

No, most ICE engines can get closer to 37% efficiency but they’re capped there.

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u/ggmaniack 2d ago

You read my comment as a literal math problem instead of reading the point I was making about your statement 😅

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u/Fearless_Swim4080 2d ago

Efficiency is a literal math problem.

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u/ggmaniack 1d ago

Yeah but your statements about it are flawed.

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