Rebel, stock 33in duratrac tires no lift.
3.92 gears
~20,000 miles +
Magnaflow exhaust, very recently also added the mopar Ramair intake.
I have mostly city driving, very little in the way of long highway stretches, and those highway stretches normally have idiot coastal drivers.
I mean idiots. Merging is a nightmare, getting up to speed involves some throttle, and unless you feel like doing 45 in a 65, prepare to meet your new friend, the left lane. Oh and get there quick, or you're doing 58 behind some guy in a prius who is finishing his audiobook on vegan cooking.
Lately I had been averaging 14.7mpg
Now with the intake, I'm getting 15.7 by the end of the first tank. I'm doing a lot of "I need to hear this exhaust and test the power delivery" driving too. I'm finding steeper hills just to have an excuse for needing to roll into the gas pedal.
If you made me guess? I think the MPG did change, with a pickup of +.5mpg city, +1mpg highway and it would show up on a long highway loop.
I don't want to state that with absolute certainty, but I also don't think it's erroneous at all. There has been an increase of some sort.