What has been the experience when installing this piece without retuning? My parts guy says that without installing SE mufflers and retuning, that there is no increase in performance. I have read in American Iron and some other pubs that it is not necessary to retune after the air cleaner up grade? I realize that this post has probably been up before but I am a new user and couldn't find a previous post that answered my question. 08 Road King, no modifications, all stock.