The muffler came with an early Chinagirl, it's the one where you can remove the endcap and baffle with a screw. The muffler came with a 66 cc Chinagirl so I'm thinking it is less restrictive on the 48cc chainsaw engine. I cut the original pipe off and welded a male 3/4" pipe fitting to the muffler so I can screw it into the female pipe fitting I welded to the exhaust pipe I fabricated from thick-walled steel conduit. I welded the other end of the specially bent conduit to a manifold I fabricated from heavy square steel pipe that bolts to the engine jug in place of the standard chain saw muffler. I fabricated a gasket from copper flashing to make sure the manifold doesn't leak. The beauty of this setup is I can unscrew the quiet muffler and screw on a standard Briggs and Stratton muffler with 3/4" threads for an unrestricted Bultaco sound. I can tell a real difference in the performance of the engine with the B & S muffler, but I like the quiet purr of the other muffler when I'm crusing through the neighborhood or town
. If I want to "get on it" and take a spin along the river, it takes me 5 minutes to swap the mufflers out (as long as its not too hot).