I have (or have had), the stock mufflers; the stockers gutted and fitted with 2" perf pipe; Leo twin slip-ons, with and without small spark arrestors; and a pair of the longer db-killer/spark arrestors that come with other Leo pipes. I used a db meter and video camera. I checked and re-checked and have been back and forth. And, it's all pretty interesting. First, with the bike sitting in the driveway revving up and down in nuetral, they're all pretty much the same. The db meter, the video and even my wife and daughter giving me peanut-gallery measurements...the sound levels are indistinguishable. This is consistent with what I could find about muffler design theory. Unless the motor is under load, you don't know what you've got. Sitting at idle, even revving up to 5k rpm, the motor is only making a couple of horsepower. There just isn't the same explosion force coming out of the ports as when you're accelerating hard or going up a hill. This is an acknowledged flaw in how bike noise is measured at tracks and OHV areas. But, testing the stationary bikes is all they can do. Out riding, I found the Leo twins too loud and wanted something quieter while still preserving the lower heat level and lighter weight. I modified the stock cans and they definitely are quieter. Then I got a pair of inserts for the Leos from Dan at MotoX. I had my son rev the bike up while I put them in and out of the muffler tips (wearing welding gloves!). My panel of judges (wife and daughter) sitting with their backs turned could not tell A from B. I was stumped. It sure seemed like these inserts should quiet the bike down. So, I rode the bike down the hill and back up again. When I rode it back up with the inserts everybody said it was a LOT quieter. I felt the same. Huge difference -- smooth and nice without any big barks. Decel popping virtually gone. Butt-dyno says the power is the same, except for what maybe feels like a little less power coming off low RPMs -- it seemed to want to rev above ~3800 to really get jumping. I'll A/B it some more and see if that perception persists. So...I'll be sticking with the Leo twins and the longer inserts. I know not everybody cares about the noise level, but I like quiet bikes (and my neighbors do, as well).
