The mileage isn't bad at all considering how much power you get. I used to average around 22mpg mixed city/highway. Now it's about 18. Of course it highly depends on your driving style. If you stay out if boost you can easily get the same as stock. I've heard stories of 25-30mpg highway. I cannot say that I've been able to do that. The best I got on a 600 mile, mostly highway, road trip was 22. I can't stay off the boost.
