I tested mileage between stock and having the tymar filter and 4" exhaust on my 7.3. I do a 350 mile 65mph freeway drive about once a month and i noticed my mileage went from 18.5 up to 19.5 mpg. Around town it made no noticeable difference. The turbo does spool up quicker and it boosts at a higher psi under WOT making more power and you CAN feel the difference. A friend of mine claimed to do better with his afe and 5" but when we made the same trip in his truck i calculated it and it was identical to mine. Turns out mods make people a little biased and start exaggerating numbers. Honestly, pumping your tire pressure from 40psi to 65psi will do more than an airfilter. I have the numbers to prove it. Great for power tho