I've experimented for some time now with trying to make my Propipe quieter. While I like the sound of the pipe, it's too loud for me these days. I've tried the clamps around the holes, fiberglass muffler packing, steel/brass 'wool', etc.
A couple of weeks ago I was sitting in the garage contemplating the issue and came up with an idea. I have several of the Propipe baffles leftover from those experiments. I thought "why not make the baffle longer?". So, I cut the inner end out of one baffle, and the outer end off another baffle. The 'plug' in the back end of the baffle was removed. I then welded the inner piece to the back of the outer piece. I now had a baffle that was twice as long as the original one.
Here are a couple of pictures prior to the cutting and welding. I have to remove the modd'ed baffle from the bike to take a picture of the finished product.
The result is a slightly quieter Propipe with, IMO, a much nicer sound. I had the bike dyno'd today and it shows a 3.4 hp/3.84 torque increase.

The whole project took about 2 hours and cost one Dremel cutoff wheel, and a welding rod.

Showing the end 'plug' that was removed prior to welding.



Showing the orientation of the two baffles prior to cutting. This is how they will be welded together.
The one on the right had the whole left end removed, leaving only the part with the holes in it.
(Of course the hose clamp and packing was removed as well)

 

pics of modified baffle please