Originally Posted by JJR
I've seen flow charts favoring both as king, that is why I wanted to do my own test on a real truck and not just a machine in a lab. My test showed me the flow and restriction of both in their installed state. AIS filter in the box and the 6637 with the obstructions around it. I am reluctant to do the fender sleave mod even though my early 99 has the ducting in the fender for it because I remember all the fine sand grit that would get sucked into the original filter box using this method. I think Ford changed this for a reason. The grit that got flung up from the tire into the box combined with the crappy sealing lid on the early99 box dusted alot of these early engines.
Well, of course, there is the inner fender well between the tire and that hole (although certainly not air-tight sealed) and not directly sucking air from what comes off that tire. Plus, the draw there is supplementary to the snorkel (especially going down the hi-way with a ZooDad). I guess if you live in a very dusty environment, drive a lot on dry dirt roads, it might be an issue. Otherwise, I'm sure the AIS media can handle the dirt quite well
As you state, the only disadvantage might be slightly shortened filter changes, Not "dusting" as caused by a poor seal that actually bypasses the media.
As for the potential flow differences, I don't think it could make "one lick" of difference to any of us
Freeing the engines ability to breath with free-flowing intake & exhaust is the important thing we're gaining.