2g Awd Dowpipe A/t

[1999silverGSX]

I am looking to buy a 3inch downpipe for my 99 gsx a/t today. I have a thermal 3inch catback. Last time i ordered a downpipe.. megan racing the flanges were to big. Also i noticed at the beginning of the cat back it narrows down a little bit maybe 2 nd 3/4's or 2 1/2. Also i plan on upgrading to a either a evoIII 16g or the SBR bastard 20g. What would i have to do if i bought a dp that works with factory o2 housing then get .. lets say a 20g would all i have to do is buy an aftermarket o2 housing that would work with that turbo?

 

[TSIMonsteR]

no, a ported 2g o2 housing will be more then enough for most applications. You can get tubular o2 housings for pretty cheap from punishment-racing.com, but thats up to you. Any downpipe you get should neck down to a 2.5" flange.