Thumbs, if you're handy with tools you can drill and tap the exhaust for a Fox .74 muffler or get a Davis Sound Master but it is a strap on too. I don't like the strap on idea either so I use the front half of the Fox muffler with a J-Tec Snuffler bolted into it, the Snuffler is suitable for engines up to 120. Or just use the Fox .74 muffler as is, but it's a little loud. It will work best with 5% nitro and a 14x6. It's a Dykes ringed engine so don't lean it all the way unless you're sure it's completely broken in. A Fox Gold Post idle bar plug plug will make it totally reliable.