I've been waiting and waiting for one of the component exhaust systems, namely Stromung and ScoobySport to create a downpipe with a cat. Thing is, Stromung makes a downpipe with a cat with a stock style opening that blocks the wastegate. ScoobySport makes a one with a great bell-mouth opening, but with no cat. I know that Graham Goode Racing makes a component system with a downpipe that has a cat AND a bell mouth opening, but after my experience with their up pipe, I'm wary of their fitment since it was created for UK-spec WRXs. But I've come into contact with a local fabricator with a good reputation, so I'm thinking of just handing a Stromung downpipe over to them, and having them create a bell-mouth opening as it is on the Graham Goode Racing downpipe.
Allow me to illustrate:
This is the Stromung downpipe. Note how there's only a hole for the exhaust outlet out of the turbo, and how the wastegate would just hit that steel wall next to the hole. But it has a cat!
This is the bell-mouth opening on the ScoobySport downpipe next to the stock downpipe. But no cat on the ScoobySport!
This is the Graham Goode donwpipe with a cutout for the wastegate and a flanged add-on on the piping. Nice idea, eh? With a cat! But not U.S.-spec. For example, what the hell is that sensor inlet right after the cat doing there?
Here's a nicely detailed photo of the stock downpipe juxtaposed to a beautiful, if catless, downpipe with a bell-mouth.