I'm getting ready to install a Tony Mamo ported FAST 90 on my 427 and before I go in for a tune I wanted some input. I currently am running magnaflow cats in my 3" true duals and wanted to know if it's worth removing them. I did a search and most seem to think a 5rwhp gain is all you'd get, but this was only for people with h/c set ups. My exhaust consists of Dynatech LT's, dual magnaflow cats, magnaflow x-pipe, dual Borla XR-1's.