My free mods include removing the resonator box, pulling the "tray" out of the airbox, and cutting out the panel over the intake "tuba". I also ran ground wires from the TB to the battery. The only thing I can report other than bitchen' music from under the hood is that it does seem to pick up the next gear better than it used to, which suggests to me that any horsepower gains may be in the mid range rather than up top. It certainly doesn't feel any slower. Fuel economy seems to be suffering a little, but I'm quite sure that is due to my right foot, not the mods themselves. I do have a homemade TRUE cold air intake in the works, as do several other 6 owners at other forums.