Matt,
My side-pipes are not stock SPF. I did a dyno pull with the stock SPF side-pipes and it was about 50HP/TQ less than what I show in my signature line. The side-pipes I'm running I built using a merge collector from Hedman Headers and a muffler from Howe Racing. Less back flow as evidenced by the dyno results, also a different sound, i.e., louder and deeper.
