Have the Flowmaster 40 series on my GTX and can't stand the resonance at any cruising speed and my wife rarely wants to get in the car for anything but a very short trip. She says it gives her a headache and liked the Dynomax stainless Ultra Flo mufflers on the '68 Road Runner much, much better. Me too hands down. The Dynomax mufflers are the same design as the stock OEM mufflers and they sound to me exactly as I remember what the mufflers on my new in '69 Road Runner sounded like in 1969......I'm old but that's what I remember them sounding like for the 11 years of ownership. First time I drove the GTX with the Flowmaster's I stopped the car to see if there was a problem with the mufflers like a loose clamp or something. Bought a new set of Dynomax ultra flo's and can't wait to put them on....the Flowmaster resonance is painful some times.


My Road Runner circa summer 1969