I believe this housing is located right before the downpipe.
Is that correct??

Some vendors offers replacement unit for this that claims better flow.
Does anyone have a picture of the factory housing??
I cant find a good picture in the EVO manual.

 

yes its off the turbo housing and connects to the downpipe, however it is probably the best flowing OEM o2 housing out there. so there really is no need to replace it

 

Yes, but the SS 02 housing is shinier, so it's worth at least 40 horsepower when combined with lots of stickers.

 

Any picture of it?? How big is the diameter of the housing?

Thanks,