Need help on a flange or 02 housing for at t25 turbo from a 90 grand prix. I bought a 02 housing off a nissan, bolt patterns match but there is still a gap. It seems the turbo side is slightly bigger(approx. 2mm) than the nissan 02 housing.

Anybody know why and where I can get something custom made.

 

Just about any exhaust shop should be able to weld an o2 'bung' into a downpipe.
For flanges go here http://www.roadraceengineering.com/h...eekerparts.htm