I have been looking around and considering a cold air box since the air boxes on the cummins are restrictive (that is what everyone says, right?). I came across this part that is approximately 4" in diameter and is sold as a modification to the current air box. You cut a 4" hole in the bottom of the current box and the hard plastic tube fits into the hole and the other end is done near the front bumper; thus, cold air is rushed into the air box. The company I saw this advertised wanted $129 for this simple modification. Well, I spent $4 at Lowes for a 10 foot, 4" diameter piece of tubing that looks exactly like that of the $129 part. I put that in and ran the other end down to the front bumper. Not sure if it is improving anything, maybe dropping my EGTs a little, but it is too early to tell. Next I'm considering a full flow through muffler, but I can't make one of those...
Bob
2003 R3500