On my stock mufflers I used a 1" hole saw on an extention to drill out the center piece. Sounded decent but not quite loud enough. Then I used the same hole saw to drill one more hole directly above the center pipe. I thought that sounded really good, and you couldn't tell it was done unless you kneeled down to look at it. For me personally though, that still wasn't loud enough. I've gotten mixed reviews though on the custom exhaust I built, so I'm not sure what I'm going to do with it when I pull it out of storage in the spring.