I got an Airaid intake and Magnaflow side exit catback, and noticed no difference in all-city driving. It remains constant at 12 to 13 mpg.

However, I was quite pleased on a recent highway trip. I just got back from vacationing at Myrtle Beach SC, and I averaged 17mpg through the WV mountains, and then 19.1 mpg on 2 separate full tanks going through NC/SC where it's flatter. Average speeds were 55 to 75mph.

This was in my 4x4 Screw, 5.4L 3.73 rear end, and also loaded down with luggage.

oh yeah, I got an Advance tonneau cover too.

For comparision, I had a Sport Trac V6 4x4 before this. It only did 2mpg better than our big trucks. (15mpg city / 19mpg WV hilly highways / 21mpg flat NC/SC highways)

 

I disagree with your premise usernametaken

Air Filter Facts read on you'll learn something

an extra 25hp to the rear wheels at 3,000rpm's is a good thing that does net you better mpg
and it sounds badass when you kick it

 

Fair enough. Note that it was published by K&N.
1st simple search returned this:

http://www.bobistheoilguy.com/airfilter/airtest1.htm
http://home.usadatanet.net/~jbplock/ISO5011/SPICER.htm
http://www.roadkill.com/%7Edavet/moto/air.filters.html

I'm not trying to rain on your parade, just giving the reasons I wouldn't use one. I'm sure it does sound different, although I like quiet, and that it make a LITTLE more power. I am equally sure that it would have no noticable effect on gas mileage, and since I drive on dusty gravel roads, I don't want it protecting my engine. Very few things are black and white, all good or bad, so you weigh your priorities and spend your monies.
Also I noticed that you had a different intake with a K&N. I have no Idea what this would do for your engine, I was just talking filters. When we were young we could just flip the air cleaner cover, and instant intake honk!
I'm too old to read, so learning's out of the question

 

Greetings all,

I've got an '04 FX4 regular cab (18s with 3.73s), with Extang vinyl tonneau, K&N, Airaid intake tube, and a custom cat-back with a Magnaflow muffler and dual tips. Recently on a road trip, not running the air, I saw 18.94 MPG. I'm not a feather foot by any means, and passed several times on the journey.

Trouble is, I never bothered to try and get a baseline number, since the minor mod lunacy began before I had 500 miles on the truck. I know for a fact that I'm getting better average mileage (city/highway mix) than I did with my '03 Ranger 2WD with the 3.0 six, and that's nothing to sneeze at.