O.k. I've searched around and gave up because I haven't seen anyone comment on this. Maybe it doesn't matter, maybe a dumb question, I dunno.

My O2 housing has a 2 1/2 outlet to the exhuast. I want to buy a 3" turbo back exhaust...well doesn't that mean I can't get any more flow than 2 1/2 inches diameter pipe?? I suppose the 3 " exhaust flows better down stream with the easy bends and a 3" cat, but still---no more than "2 1/2 inches" of exhaust can flow in the first place.

I'm I missing something??

 

You're not missing anything. More O2 housings are designed to use the stock donut gasket, so they all are nearly 2.5 inch outlets. The internal design is what aids in the flow compared to the stock piece. Having said that, you can get a custom one one made. There was a member who made his own housing with a 3 inch outlet, but it was a one-off piece that used v-bands since there weren't enough room for flanges. Beautiful piece too!

 

There is a couple companies that make 3" O2 housing. WORKS and Invidia.

Here is a comparison I did on 2.5" vs 3" O2 housings.

https://www.evolutionm.net/forums/ev...-housings.html