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So the Mustangs' would be the small chin scoop?
The Allison had a downdraft carb and so the intake for the carb is on top in the P-51A. The Merlin has an updraft carb and so the intale is under the spinner on the P-51.
The intake for the P-38 is a small stand-alone scoop under the traling edge of the wing on the booms. In modern P-38's, nobody is running the turbochargers and the carb intake is in the middle where the intercooler intake used to be.
It seems (to me) that razor1uk and nuuumannn are in disagreement.
The little scoop on one side of a Spitfires cowling, is for (partial) cockpit pressurisation using a roots type blower
All Allisons except some unsupercharged PT boat and tank engines had a carburetor that fed the air fuel mixture directly into the supercharger impeller and was compressed and routed to the cylinder via the intake manifold system. Supercharged Merlins, both single and muilti-stage, were the same except the Allison has a downdraft carb (carb sticks up ... so air intake is routed above the engine and turns downward into the carb) and the Merlin has a updraft carb (carb sticks down ... so air is routed under the engine and turns upward into the carb).
That's why the ALlison-powered P-51A has the carb intake above the spinner and Merlin-powered units have the carb intake below the spinner.
The -147 and -149 Allisons (the G9R and G8L for the F-82) had fuel injection, but the supercharger was in the same place with the air being routed to it instead, bypassing the space where the carburetor used to be.
Early P-38s were ordered without the turbo charger by the British and French, but I don't think that was because of a "ban" they wanted all the engines to be the same as I understand. There was some sort of embargo on selling turbos abroad which lasted into the 70s but I read about that with regard to aftermarket bolt ons for motorcycles.On a separate question, since you seem to have a lot of knowledge of the Allison engine, was the Allison every used in WWII combat without a supercharger in an airplane? I am having a debate on Quora who alleges the Mustang I used by the British did not have a supercharger. He writes that supercharged Allison engines were not allowed to be exported from the U.S.. This I assume to be a misreading of his literature. thank you.