The part number for the muffler is SM-Q4LGS. It is in stock. I think it was round 40 dollars or so. Thats almost 40 dollars cheaper than the slimline's muffler. Actually the davisdiesel muffler is actually a muffler. It has a baffle inside which quiets the exhuast alot without taking away from power. They said that it actually increased power by a couple hundred rpm.