Keep your exhaust stock and youll get good gas mileage. Soon as you change 1 part of ur exhaust system your gas mileage goes down b/c you like to play around with the loud padel to much.
Example: Instead of shifting @ 2200 rpm.. you instead shift @ 3000 so you can hear the 2500rpm sweet spot sound plus the extra umph from the exhaust pipes.
Instead of starting at first gear and shifting @ 2500 you gun it in 1st and shift into second @ 5000 rpm just to hear the exhaust.
Or You downshift into 1st from 3rd just to hear the exhaust roar and pop than you gun it and shift into 2nd.
boy do i have to full up my car every other day ;] it seems
i think 30 is possible for freeway