I have just been using the K&N air filter itself in the standard air box - given I have to keep the air sensor anyway it didn't seem much sense to convert it - the K&N air filter itself makes a huge difference in free flow into the engine (with engine throttle response, etc). I am running 14psi boost with rocketchip and it goes very well (I use it on the track mostly and the power boost is fantastic on the straights)....the standard air box (in oz) are very open underneath compared to the NA which were closed (I drilled a lot of holes in the one I had for similar effect). The XR2 air box doesn't need any more holes in it....