I have a customer that was not running his scoop sealed and the insides on his engine was trashy every time I tore it down. I Finally made them seal the hood scoop. Bammo, next tear down engine was fairly clean. I have one now that refuses to use a hood scoop at all with an injected EFI engine. We will see what happens there.
It is my theory that a good hood scoop increases ambient atmospheric pressure levels.
Ed