Ok I am very confused. If I buy a catback system for a WRX and a downpipe, is the third cat still going to be in the exhaust track? Do I have to build or buy a test pipe to replace this length of pipe where the third cat resides? Please help I am making this such a big deal that I am giving myself a headache. I know if you buy a turbo-back exhaust this eliminates the cat, but if I use say a invidia dp, and a JIC titanium catback am I still going to have to build a test pipe? Thanks in advance.

 

usually, aftermarket dp for the wrx replaces both the stock dp and mp. i believe the invidia dp mates right up with the cat-back.