Just question. My Mustang GT has a 2000 GT motor and under coasting conditions or deceleration it backfires a lot (it will backfire all the way down a hill and that is all I hear). I have a exhaust company called Blue Streak Glass packs. And at idle it is not as smooth of an idle unlike other GTs I have heard. Would the poping be from a mild cam and it is leaving valves open a little longer. And when i blip it at arond 2200 on a blip it would have one loud pop or backfire. It sounds cool. I cannot believe all the poping is coming from the glass packs.