I just got a 2004 mustang and was told that i should put a flowmaster 44 on it and have them cut me an exhaust to make it duel exhaust. I don't know a whole lot about cars but i was wondering if doing this would make me gain/lose mpg and if i did it how much would i gain or lose. So could somebody who knows what they are talking about please help me.
If it has any effect on your MPG it will be very miniscule. Depending if you hit the gas harder or take off a little harder to hear the exhaust then the mpg could go down. If you don't, then it'll stay the same or maybe just slightly improve (Barely noticable) but it could up the mpg.