I lost mpg on 3-4 miles around town and the back pressure dropped differently. Not sure if it means the best sound damn it's on my Dodge Durango 01 4.7, I paid $60 for the Flowmaster + $20 for a 3 inch tip and $100 for the weld and pipe from kettle to tip, so $180 for installation. So let's say I drive 1300 miles round trip. I'll post my MPG petrol in an update to see if it's better or just louder than stock