This is the one I got
http://www.knfilterchargers.com/search/ ... od=RX-4870
Its on my CAI which is made for the V6, so I assume its the same diameter as the V6 w/ CAI. (Filter that came with my 4cyl's Injen is 2.5" and would not fit on my CAI. This one is 2.75". I had a cheap 3" one before this, and I think the Inner diameter was too big since the CAI piping was smaller than the lip on the filter to make sure you dont push it on too far. 3" worked too, but it needed to be crimped down more.)
Its also got the Xstream flow top, maximizing airflow, and a 6.5" element, which I believe is longer than Injen stock by about an inch.
Cheapest I was able to find it was $55 here. I ordered it from here and it came in good time:
http://www.ajusa.com/cgi-bin/knfilters/ ... 40cbcde4e2