I have a 97 Powerstroke with a full 4" MBRP exhaust but i also want like a single 8" stack too. What i am looking for is something like a valve where you can either have the exhaust run through the stack so you can show off to friends or you can go to the MBRP and have a little quieter ride. I have found some sites where it uses a flapper but you would think the flow would tend to run through both. Does anybody have any good sites where i could find one.