you didn't say what engine you need a muffler for ??

many people, including myself, complained about the Slimline "Tube" type Pitts muffler for their 61 to 91 size 2St, they had tuning problems, some people felt the muffler didn't produce well enough pressure for the fuel tank,, but today Slimline has a new "Q" Pitts mufler that has a larger chamber than the older Tube muffler,

as Hobbsy said, Bisson has some good stuff for sure, you can buy it just about anywhere

Jim