It is just my opinion but I think Injen RD CAI made a big difference in performance on my 03 TL S. It was the first thing I put on when I got it. I went with the RD version (long type) which goes down to just behind the bumper. The colder air works better and was a perfect fit for me. Even when I put on my P2R TB spacer I didn't have to do any modifying or cutting to the CAI to make room. I do recommend getting some 1/4" vaccuum line to reroot and replace some of the lines around the TB & CAI. There is a metal double tubing bracket which one line from the new CAI unit will replace but the second line is attached to the one that is no longer used. The metal tubing bracket just hangs there next to the CAI and looks crappy.
Once I get all the AN sizes of the hoses, I want to redo my lines in silicone ones from StylinMotors.com. I know this is way more info than you asked for but it ties in a bit if you plan to go further with your air intake system.
I hope this helps you some!
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