you're probably on the throttle a little more than you used to. if you like the power of the mbc, but would like better mileage too, i'd look into a solenoid system so you can switch back and forth between the stock bc system and the mbc. you pretty much get the best of both worlds. actually, i don't really switch the mbc on unless i want to play around racing or on the back roads. i think the stock system does a much better job of mixing boost control with throttle position, which relates to better gas mileage. my mbc is off probably 90% of the time. my gas mileage is getting better as the car builds more miles, as i've read its supposed to.