Which of these brands of pitts style mufflers is better? More specifically, I need a pitts muffler for an O.S 91FX, so who will make a better one, Bisson or Slimline?

I've used both and in my opinion they both perform equally. The shape of the muffler and availability for a specific engine are usually more of a determining factor tha the performance of the muffler. Of the two, I usually use more of the Bisson mufflers than the Slimline, but there's no real reason why other than that's what the LHS had in stock.

Ken

I have a Bission, no prob's here ..

Had a Slimline and the screws wouldn't stay in the thing. The aluminum seemed very soft. Have 3 Bisson's and have had zero problems.

I dont consider either one of these actual mufflers . the only true muffler ive seen, Pitts style ,is imported by Davis Diesel.