The stock OS108 muffler robs power and adds a lot of weight. A 108 works well with a Macs 15cc muffled tuned pipe. They are easy to set up and IMO a must have item worth about a thousand rpm over the stock muffler. They do have a big carb and need to run 10,000 rpm or more to draw fuel well. My 108 has turned an APC 14-8 at 11,400 for over one hundred flights on Omega 5%. I recently lengthened the pipe and installed an APC 15-8 that tached 10,000 on the same fuel. I would pay up to $190 for a new one.