I want to install two into one thunderheader on my 2007 and I am getting conflicting answers on what first must be done. I have been told that a HD Racing Tuner, Power Command or a Terminal Velocity (Terry Components) must be installed first. Had another mechanic inform me that if I just put the Thunderheader on and don't change the Air filter it is good to go. I am not interested in more horse power just sound a good runability. Any suggestions?