I would highly suggest using an OEM '04-'05 USDM STi uppipe along with new factory gaskets if want to avoid possible issues with leaks.

You should be able to order the OEM uppipe from Mastro but there might be a less expensive vendor online. <shrug>

 

yeah, that HKS downpipe isnt worth it.. put it this way, a buddy of mine tried my dp on his wrx with an identical dp as the hks and his boost control and power were much smoother. I would assume it was directly due to the better wastegate flow, but he is looking for someone to weld up a wastegate dump because this design sucks something fierce.... btw.. out of both the HKS and the greddy BOV i would think about the HKS, it worked much better for my wrx being MAF, without compressor surging it closed at idle, the greddy never managed too, except when i was stock however, i ditched all that shit and ive got the best bov ive used, strangely, its the quietest