I tried mine wide open....then with 6 then with nine, then with 12...
ended up going back to open.... 12 was ok, and felt a bit more tourqey..( just slightly)
with 6 felt super tourqey but absolutely choked out at 4k rpms....
9 was a decent comprimise, rode it for a day then took it all off to see if I felt a difference,.... never put the discs back on.....
I'll run 12 discs for less noise if I want to be stealthy...runs and sounds darn good wide open.. its just a muffler, if I had unlimited access to a dyno I might use the discs to fine tune it some...