If you have ever heard a motor with a big prop on a reduction unit.. with a quiet muffler..you will love it !

There are some great pics and info on this thread. I am going to add a link to a easy down and dirty muffler a buddy and I have made for 25 cc conversions...

We took a aluminum conduit box and cut it so the threaded side outlet was still hooked to one flat side of the box..That becomes a flat plate that we screw into the exhaust outlet of the motor...we used this as our exhaust mount, than we took a cheap round lawnmower muffler and it screws right into the manifold.. we drill some extra holes thru the baffle..or split the can to modify it inside. We also would use a brass screw to pin the muffler to the header so it wouldn't unscrew.


https://www.youtube.com/watch?v=Ec5g0HUQcP8