Here is the inlet adapter bushing installed in the 2 x 2.5 exhaust reducer.  It’s a snug fit (lite drive fit).  It gets locked in place by two 8-32 countersunk screws.  Once the reducer is installed in the muffler, it’s permanent.  It’s not easy to remove once the muffler is assembled.   The large hole in the side of the reducer is for my O2 sensor.  If you’re not running an air/fuel ratio meter you don’t need the hole.

Here’s how the adapter bushing is fastened to the baffle tube with countersunk screws.

The center plug is carved out of a 1-1/2” galvanized pipe plug, another routine item available at most hardware stores.  

The plug looks like this once its installed.  It will force the hot exhaust gas to flow out through the perforations in the baffle tube.

There are a total of 216 holes drilled in the baffle, 108 on each side of the plug.  The holes are 11/64” (.17”).  A drill-press works good but a hand-held drill will get the job done.  Make sure to clean up all the burrs.

The exhaust pipe expander works great for holding the work piece.  It also comes in handy for installing the baffle into the muffler.  You don’t need to tighten it very much, just enough to grip the pipe, not enough to expand the pipe.

To accommodate the O2 sensor bung you have to drill a 1” hole through the muffler and the reducer.  The thin wall material requires that you use a hole saw or a step drill.  Step drills work really good and they don’t tear up the thin wall material.

When it’s ready for final assembly, pile on the JB Weld Extreme Heat Paste and insert the bung through the inside.  Apply more paste to the threads and install the threaded collar.  The small bolt and nut are only used to hold the bung in place while tightening the collar, then remove the nut and pull the bolt out from the inside.