So I just bought a 2004 WRX and it has a downpipe to a muffler. According to the owner he says its a catback but its not, and was wondering if I remove the muffler, do I need a tune? Right now its running a stage 2 tune, that's as far as I know. Thanks! 

Sounds like it needs tuned from stock for that.. A Cat Back exhaust needs no tune, but a turbo back does, and if the up pipe is a catless pipe, then for sure it requires tune. I may be tuned correctly but that is a chance you take.