I use an extension for a electric dremel with sanding paper - working it with some fine paper and then hit it with some polishing compound. I'm a bling junkie though.
The concept for me is - on carb cars, usually keeping a mildly rough surface helps to atomize the fuel and oxygen as it tumbles through the intake track since carbs doent mix as well. However, w/ EFI - since the injectors spray pattern is MUCH more precise and accurate than a carb's squirter/metering block/jets, the fuel and oxygen atomize earlier/better, so you want as smooth as possible surface to accelerate the mixture...
Dunno, kind of old school logic, but makes sense to me...
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