I'd imagine that you get some ram effect, although how much with a NACA duct I'd question, but most of all you get atmospheric temperature air - which is going to be 30-40 degrees cooler than engine bay air.
@Dammit started
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I'd imagine that you get some ram effect, although how much with a NACA duct I'd question, but most of all you get atmospheric temperature air - which is going to be 30-40 degrees cooler than engine bay air.