sorry, typo, stock was 18.9 not 17.9, so stock was 18.9(combined maybe a 70%hwy 30%in town ratio) K&N drop-in went to 19.9(same driving conditions), and intake got a consistant 23-23.5 in same conditions. i got 23.5 3 times(but not in a row), same gas station(citgo gas) and same pump(pretty good reason to keep going to that pump lol...), 87 octane. truck was 04 f150 heritage XL reg cab longbed 4x2 4.2L V6, 5spd, 3.08 open rearend, only mod was the intake and i used mobil1 extended performance oil with motorcraft filter if that matters any. it also sat pretty low in the front but was not lowered. in winter time the 490Lbs in the back and the winter mix fuel took it back to 18mpg. wish i still had it so i could prove the numbers but i traded it from an annoying random vibration. my 08 has the same intake but it only gave it about an extra 1-2mpg on the highway. i know, a few people have said that 23.5 cant be right but that truck did it, no i cant prove it, just personal experience. its actually better than my 97 2.3L ranger got with a K&N drop-in and a 5spd, just wish someone else would get this to happen too lol.
basically just saying, my truck got that mileage, i know it did, if you believe me...cool, if not...oh well.
this was the truck and also more pics on my cardomain http://www.cardomain.com/ride/264706...50-regular-cab