It bolts in place of the cap on an exhaust dump or takes the place of the plates in the Borla exhaust. Its got a button that you push and it opens or closes the cap. Full open headers or full closed through the muffler. Kind of cool, just no plans to get a hot rod in the near (or distant) future. I don't think it would be that great on my lifted Trail Blazer or the wifes Aveo.