I may have found another reason for 'popping' during taxi etc. 

After my flight today, I noticed the exhaust pipe from the two rear cyl was hanging down next to the nose gear leg.  It broke at the last weld with the support brackets keeping the pipe from completely leaving the aircraft.

Both pipes are (were) supported from the rear oil pan bolts in a triangle shape using 1/2" SS tubing. I intended to have the pipes move with the engine.  Recently a couple of friends commented that they thought a 'popping' noise was heard as I taxied to take off.  Perhaps a crack at the weld had started unnoticed by my engine inspections.

I would suggest a close inspection of all weld points.  I only have 125 hrs on these exhaust pipes.  BTW the exhaust was discharging on the fuel line from the engine driven pump to the carb.. good 'ol fire sleeve to the rescue..

If anyone has pipes for a 0-320 DIF of the type supplied on the early 235/320 kits, I would be interested.  Thanks, Earl