Here is straight from fast wrx.com
If you want to keep SOME of your factory catalytic converter hardware intact, this "shorty" downpipe is for you. It replaces just the stock downpipe/cat, leaving the midpipe (with its rear catalytic converter) as the factory made it. The divided wastegate outlet makes for excellent flow during full boost conditions. All stainless construction.
I researched and you can run cobb stage 2 with this downpipe but make a little less hp. Some claim no more then 10hp and cant feel diffrence on stock turbo. It has braket cut off because you dont need it they started comming like this from the factoy after the first models. It was $250 brande new with shipping. Just a little info also will fit stock exhaust.