Does anyone know what the function of this part is?

juld0zer

it does act like a baffle of sorts. how effective it is, i'm not sure.

but i'll give you my 2c. the Stillen G3 CCV barb on the right hand side pipe (bank 1) is narrower than the diameter of the stock accordion pipe's CCV pipe.
because of this, i had an idle which kept sagging when stationary. i cut off the Stillen barb and welded on a larger diameter barb and the idle was rock solid afterwards. No ecu resets or relearns were performed either.

so, if you plan on deleting the CCV barb on the stillen pipes, my suggestion is to not do it. after all, the ccv system on our cars works by drawing away the crankcase fumes and drawing in fresh air at the same time. that volume of ingested fumes is accounted for in the combustion calculations by way of the MAF sensor because the fresh air that gets drawn into the crankcase to displace oily fumes comes via the Stillen pipes. I hope this hasnt confused you too much what i'm trying to say is that you dont want any unmetered air in the system (eg. by fitting a small pod filter and blocking the barb on the stillen