Sorry im late, I just found this site. I too have an 04 super glide and have a few things to add, but as far as the mpg. Goes mine gets between 40_50 and i found that tire OSI had allot to do w/it. And although I have nothing to compare it to, I´m running Vance & Hinds short pipes that came on it. They are nice and loud and extreamly safe.