[dsraven]

I have a version of that in the exhaust of my road bike. it is 2 head pipes into one larger rear pipe that has a slip in section similar to that which necks down at the tip. the difference is that at the front section there is what looks like the end of of a tin can welded on with a section of the inner pipe protruding through. this ensures that all the flow goes through the inside of the pipe with all the holes in it. the outlet end of the pipe has the same thing. that donut shaped blockers are formed so they have a flange that fits snugly inside the outer pipe and the rearward donut has a couple of screw holes so the whole thing can be retained inside the outer pipe but also can be removed for service. the area between the 2 donuts of metal is then wrapped in what looks like dirt bike exhaust silenecer material. this material burns out in a summer or 2 of highway riding. the slip in part can be pulled out and repacked. I have used stauinless steel wool wrapped around the smaller pipe and then a length of galvanized sheet metal from home ducting that I had laying around to keep it all together. then I keep it all in place with a wrap or 2 of stainless steel wire. if you find the tip seems to do the job you could easily make a larger pipe for the tip of the exhaust system that would allow you to have a larger diameter slip in part such as the motorcycle has. just a thought. my bike is still quite loud and has the sound of a bike bagger harley but without the slip in you wouldn't want to ride it far. it would be less loud on a truck like yours because you actually have a muffler. this is the muffler on my road bike.