Does anyone know what this 4 barrel carburetor was originally used on? It's a 400 CFM Carter AFB square bore. I am wondering if it would be a good candidate for a Turbo blow through Slant 6 and how much HP it would support? Just need a carb that can make @250-275HP...Any/all help appreciated!

A 9400 is an aftermarket performance carburetor not intended for any given engine. It should work just like any other AFB when boosted.

Two things might be a problem with a blow-through AFB. #1, The hollow brass floats might colapse under boost,I had this problem with a BBD. #2, without an air box around the carb, boost pressure might force raw fuel past the accel pump rod were it goes into the carb.

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V8?? We don't need no stink'n V8!!