on my old hatch i had a b20 and it was turbo with 2 1/4 turbo back exhaust witha apexi universal muffler and it wasnt loud at all. It didnt have a cat either. But what i would do is take your high flow cat off cut it open weld a pipe in there so it is a "test pipe" and then weld it back up. It appears to be there but you get the flow your after with the turbo.