hi did a search on this couldnt find any answers, just wondering if replacing a stock 03 sti downpipe with a prodrive cat downpipe is a worthwhile mod?, and also is this going to be compatible with a full miltek sports cat system along with gt spec headers which I currently have? appreciate any comments. cheers

 

The stock STI downpipe has a cat, The prodrive downpipe is a sports cat which will give you more horses if mapped, Only thing is i`m a little confused as if you already have a milltek sports cat why would you want a prodrive item, Not really much difference between the two, Tha prodrive sports cat has a 2.5 in bore , not sure what the milltek has though, Gaz.

 

The best thing you can do is totally decat and pick up extra power.
With the GT Spec 3 bolt headers you will get a big benefit from changing the uppipe to my 3 bolt special uppipe. If you want independent feedback on that do a search on here and listen to those that have one of these actual uppipes.