I know LS intakes are generally 2.5" piping and ITR are 3"...not sure about GS-R offhand.
This is for an FC right? I lurk over at rx7club and have caught a couple of your posts over there.
Stupid as hell how all the intakes are basically just filters to stick on the end of the stock intake. Although isn't the AFM at the end of the pipe and the filter just stuck on the end of the AFM box?