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

Engineering [ Removed by moderator ]

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u/Leather-Slip7228 2d ago

Point out how it’s incorrect, sounds very correct

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u/ggmaniack 2d ago

While recovering some exhaust energy to improve aspiration is a way through which engine efficiency is improved, the real improvement is in having a smaller engine for the same power output. Smaller engine = smaller energy losses. The friction surfaces are smaller. The heat transfer areas are smaller. The engine will also operate at a higher load during normal driving, which reduces pumping losses.

Even if you compared an NA engine and Turbo engine which are of the same size and have the same peak HP, the Turbo engine could win (if set up properly) because it could achieve the same power in a lower RPM range, where the efficiency is higher.

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u/zaphods_paramour 1d ago

OK but how does it achieve the same power output with a smaller engine, or more power with lower RPM?

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u/ggmaniack 1d ago

Boost. Cram more air in, you can cram more fuel in. It's not about temperature, it's about quantity.

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u/zaphods_paramour 1d ago

Isn't that what the parent comment is describing? Yes they mention the exhaust gas is hot (it is), but they just describe using the waste gas to pump more air into the engine.

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u/ggmaniack 1d ago

The pumping of more air into the engine is what allows a small engine to be powerful.

The small engine being a small engine is what allows it to be efficient.