I did the clayton mod on my 05 1300C today. I want to get a complete exhaust at some point, but it's kinda cost prohibitive just now...this was a decent short term solution. I started with just 5 holes, and actually haven't drilled 1/2" yet as detailed in the original posts (my tool box is as skimpy as my checking account- have to get a chuck that'll fit it!)...but even as is I like the sound better. No backfires or noticeable changes in performance, just a little better sound.