The stock O2 housing is restictive on the SR20DET.
If you are upgrading your exhaust to a 3" you should also upgrade your O2 housing.
The new cast 3" O2 housing from Circuit sports is over 100% larger then stock.
It has a true 3" pipe to increase exhaust flow for more power. Most other O2 housings are 2.7"
Cast pipe makes the inside of the pipe very smooth which will reduce turbulence.
89-94 240SX S13 (T25 setup) Part No.: TBO-2130-LC
95-98 240SX S14 (T28 setup) Part No.: TBO-2140-LC
I was skeptical at first on buying this part but after reviewing others and comparing this one to others I gave this one a shot. Circuit sports provides everything you need for the install. Kit come complete with studs nuts and washers for the turbo and for the downpipe side. Gaskets are also included and the 5 bolt gasket is OEM like quality. Turbo elbow is cast so so the only weld is on the the down pipe side but on the outside. No grinding marks on the welds inside of elbow like the others have. Only down side (very minor) is it s easier to install while turbo is out. Bottom middle nut is the hardest to install while turbo is bolted on but everything else is perfect. Well worth the money.