After reading @jebbesen 's post about the headers and mufflers he built, I thought I'd throw this out on how I build mufflers. First of all, here's a link to his post: https://www.jalopyjournal.com/forum...school-driveshaft-headers-side-pipes.1131726/ The first set I built were for my 1956 New Yorker, and here's a youtube link to how the pair behind a stock 354 hemi sound: Those are a two-chamber version. The photos below are for a 3-chamber muffler, and while I built it for an O/T vintage thumper dirt bike, the process is the same, just scale it up. First of all, here's the inside pipe for the muffler before drilling. I calculate the number of holes I need to drill per chamber based on the area of circumference of the inlet, and upsize it 50% or so. The ring around the outside is a chamber separator. You need to put it on before drilling holes and making "scoops". Chamber separation inside the inner pipe is done using appropriately sized core/frost/freeze plugs. Shown here are the first and second chambers separated by a core plug inside the pipe. The holes are drilled and then a round shaft screwdriver is used to bend the holes into "scoops" that face the exhaust flow and grab the exhaust to direct it from one chamber to the next. The inlet is on the right, so exhaust flows into the pipe where it is forced out of the first set of scoops due to the core plug block which is in the pipe between the first and second groupings of scoops. It is forced back into the second set due to the ring on the left forming a seal between the inner and outer pipes. End caps. More core plugs, these the diameter of the pipe used for the outside of the muffler, and cut to let the inside pipe pass through. Easy to do on a lathe, pain in the ass otherwise. The three chambers, from left to right. The exhaust flows from inside to outside in the first chamber, outside to inside in the second, and back out through the third. I wasn't finished drilling the more numerous smaller holes in the third chamber, was still doing some math to determine the area of the holes I would need for flow. The ring on the outside between the second and third chambers is sized just a few thousandths larger than the ID of the outside pipe for a nice press fit. Once again the lathe is real handy to sneak up on the proper size. A view of the inlet, with the inner pipe pressed into the outer and tack welded. The drill chaff in the holes helps to soften the sound. They will eventually rust, break off and blow into my buddies face who always rides behind me. Side view of inlet end. Core plug tacked into the outlet end of the inner pipe. This is at the end of the third chamber, forcing exhaust back into the space between the inner and outer pipes. Another core plug the diameter of the outer pipe is welded onto this end, with a short curved outlet. Normally for a hot rod application the outlet would be straight instead of curved. As mentioned earlier, this particular muffler is for an O/T vehicle, and needed to have the exhaust directed to the side. The finished muffler at the top of the pic. You can ignore the lower item, it is a piece of plumbing that goes between an engine and the muffler I built If you're interested in the effectiveness of this particular muffler you can click the link below. This video was taken immediately after starting the engine, so no burned hand.