I never ran it on a stock motor so not really apples to apples. I ran it on a lower than stock CR motor (8.15) and it made low 700s I recall. Then I had it on a 10.5 CR motor with ported heads, cams, 1 7/8 long tubes and a bunch of other stuff. I also cranked it up to 30 PSI on that setup and it made a lot but isn't fair to compare to stock engines. It also couldn't keep lower pulleys in one piece.
As for belt slip a good idler next to the blower makes a world of difference. A thump tensioner is fantastic too. I've also had the machine shop slot the blower pulley and any belt will grab in there really hard and you get no slip.
People are also now lightly sand blasting the belt wrap surface of the pulley to create a rough surface with more friction. I've never needed to so I've not personally tried this so not sure how well it works.
