I find mileage depends on how you drive it. I have a 2 liter Zetec, ITBs, Emerald ECU, stage 3 cam,and I can go through half the tank in 20 minutes at a track day, or about 5 gallons. If I drive it in a less spirited manner, I might get 20 MPG, but what is the point of driving it if I just putt around? So, the 20 mpg is more theoretical than something I've verified.