I've had the standard muffler on mine and now I have the Slimline pitts muffler on it. I get a little more rpm out of the motor with the slimline. But I'm also partial to slimline's mufflers. They are of superb construction and stylish. I have them on just about every engine that has required a pitts. 2 strokes, 4 strokes, gas ...you name it. DA sells the Slimlines!