what is this part?

[kenkamm]

I haven't looked at the shop manual, but that looks like an intake resonator. Usually added to make the intake sound the way they want and/or remove an annoying resonance. Removal of such a device might make for more/better or sometimes worse sound. I don't think you'd gain or lose any significant power, though, unless it's designed to be part of the intake runner's tuning.

Someone here can correct me if I'm wrong.

[djomlas]

when i had my last car for a short period of time (WRX), it had one of those baffles as well.
it was pretty much the whole wheelwell, i removed it and the sound of stock BOV went up, as did the overall sound when the gas pedal was down.
so i hope thats what it is.

has anyone taken this off befor and is there much of a difference?