Attached is a reduced size scan of sketch of the muffler I have just downstream from the tangential muffler.

 

The idea is to further reduce the pulse peaks by forcing some expansion through the holes, and back to the center pipe. 

 

If I were doing it over, I might look at something different for the restrictor orifice that doesn’t give a straight shot through the middle.  Maybe two half circles rotated 180, with some space between.  Keep in mind that you don’t want it to cause much back pressure, and that the material in the internals is going to get quite hot. I used 321 SS for this, and when I first designed it I expected it may be subject to failure in as little as 50 hours.  I now have over 150 hours, and no signs yet of any deterioration.  Since I have only a short exit pipe after the muffler; it is easily inspected.  The reason it is enduring well is that it is downstream from the tangential muffler.

 

Dyno runs with and without showed no noticeable power penalty.

 

Of course it’s proprietary, and there’s a $200 royalty for each one builtJ. (Or, if you actually use the design, maybe you could buy me a beer sometime).

 

Al