Nada.
I just added the OSCAI to my 2k 5spd today. I used the rubber reducer and a shop vac hose extension (the rigid smooth walled nozzle extension). It's long enough to run through a hole in the wind deflector at the bottom of the engine compartment.
Not really any noticable power change, and not much noise change either.
I've always heard it takes 25 hp to feel a difference. Maybe between this and a Y pipe I'll get to where I want to be.

I also added a FSTB. At least there I could tell some difference.