The pictures and sketch should provide you with a general idea where the mods are done.

I drilled through two of the 5/8-18 UNF bolts with a 7/16" bit.  To make things fancy I cut back the undersides of the bolt heads so that the corners of the hex head don't contact the interior of the muffler and prevent a decent seal.

Then I bored out one side of each 90 degree fitting to accept 1/2" conduit.  I wanted to set it up with a slip fit to accommodate expansion.


Here's a pic of the fittings & bolts.

Once I had the hardware fabricated, I cut a section of 1/2" electrical conduit to a length that would provide about 1/8" axial movement when everything was assembled.  I wanted the conduit to be able to expand and contract without being restrained.


I assembled the fittings and conduit and installed the end cap with attenuation tube.  It was time for a sound test.  I was concerned that the sound level would increase to a point that was unacceptable to me.


Here is a pic of the assembly prior to the sound test.

After I drilled the five 3/16" diameter holes in solid plate "C", I reassembled everything and gave it another sound test.  It was a bit louder but still easily passed my personal evaluation.  This thing is very quiet.  Very, very close to stock.

On the poor man's flow bench the backpressure registered at 27-3/4" H2O.  So the backpressure was reduced an additional 1-1/4" H2O.  I thought it would be more but I'm not gonna look any gift horses in the mouth.

I took it for a road test and it was sweet.  Very quiet, no afterfire, good power all around.  It felt a little light on fuel so I upped the main jet to a 152.5.  It really came alive after that.  The modified muffler really compliments the airbox and cam.  With everything working together this thing really scoots.  It loves the freeway.  Screw it on and it just goes.  I love it.  It might even be able to take a 155 main.  


Here's a pic of the modified exhaust with the extra transit tube.  Ooops! Can't see the tube?  That's cause it's pretty stealthy.

Here's a shot from down low.  You get a good view of things from this angle.

I'm pulling this old post forward so Junker can get a look at what's should be inside his stock muffler.