Hi Dave! That thing looks hot!!! You do sheet metal and welding? Reason I ask is, I see a lot expansion chambers being used out there. Built my first one from scratch 45 years ago, and used to have the formulas for very specific tuning. Almost any expansion chamber, however, is a big improvement over a muffler, you know well, I see. Straight though/glass pack silencers are also the norm. When I was racing all those years ago, I integrated the glass pack by welding a sheet metal cylinder from the fat part of the pipe to the end of the stinger, perforate the stinger, pack it, and cap it. This saves some space and is quieter. BUT, I was still looking for less noise on my enduro/crosscountry bikes. Instead of perforating the stinger, and packing, I simply capped the cylinder and welded a second stinger sized pipe extending anywhere from 5 to 7 inches into the cylinder. These pipes actually were pretty pleasant sounding, AND boosted mid range torque very well. I used this design on my Stihl 23cc. If you want all out speed, keep the glass packs, if you're going trail or urban, try the baffle can. Happy building/riding.
