Originally Posted by ProfessorDave

DonV, I am very impressed with the stock intake on the Z. The filters seems to be restrictive, and K&N (or another brand of more free flowing filter) seemed to be the way to go. Combined with a cat back exhaust, K&N's add a breath of fresh air (sorry for the pun. Had to do it. Had to.).

The Stillen G3 makes good power in the upper range, but is 3X's the cost of K&N's and required removal of the front facia and cutting of the front cross member, ruling it out for me. The sound is great, however. More pronounced at WOT than the K&Ns (which does yield some good sound nonetheless).

Definitely search here. You'll find some great data about the K&N's, both in terms of gains and the ability of the stock boxes to keep air temps close to ambient.