A feew days ago i postsed that in an attempt to reduce air inlet restriction to the stock air filter, i had modified the inlet tube from the fender well to the air cleaner. Several guys have asked for a photo. I made a gallelry called "air inlet" with a couple photos.
When i took off the stock air filter and tube for inspection i found the air filter was a cone 4-5 inches in diameter and 4-5 inches long. It has gobs of surface are for air inlet. The tube attached to the air box is 3.25 inch diameter or 8.3 square inches of area inlet. The other end of the tube necks down to 2 inches and pokes thru a 3 inch hole in the fender well above the drivers front tire. 2 inches in diameter makes the inlet 3.1 square inches of area inlet. I dont claim to know what inlet would cause some restriction, but it appears this tube is the point of "most" restriction for the air. I think at 3000 RPM that might make a difference. I only run 1700 RPM down the road so this modification does not add any "power" or "gas milage". That might be different if you are running the motor at higher RPM. The modification does add a slightly "throaty" sound to the motor when under acceleration, but not enough that one would notice or call it loud. I show a photo of the original tube and the replacement PVC coupling in the photo album. This has been a couple years ago so im a little vauge on the acutal steps, but i had the air box off, bored out the plastic PVC coupling about 1/16 inch so it would slide over the air box. I then installed the unit and butted the coupling up aginst the fender, does not pilot inside.

 

2001 Ford F150 4x4 - air inlet tube