ORIGINAL: Scamper
Can you fabricate a muffler using silver solder, or will the exhaust temperature just melt the joint?
Not likely the joint will melt, since most silver solders' liquidus is at or above 1000 degrees F.
Whatever base material you plan to use, J.W. Harris have a solder to do the deed, steel to steel, steel to aluminum, or aluminum to aluminum.
You may need an oxyacetylene rig to use the high silver versions, and you may find the smaller (but much hotter flame) easier to use than the whopping lower temperature flame of a propane or MAPP torch.