Vetterman has been around a long time.... Never had one. However there are other makers of exhaust you may want to explore.... AWI comes to mind. I know Vetterman sells cross overs and four into four separate pipes. Those are fine. I am a fan of 4-into-1. Vetterman did test and showed there was no big advantage of 4-into-1 over the 4-into-4... which they sell. 4-into-1 Vetterman tested was not optimal. However 4-into-4 is good, and better than cross over. EAA CAFE foundation.... found that scavenging from the 4-into-1 was superior, but the primary pipe lengths/Dia and collector diameter and length have to be sized correctly.