I did a little testing on my newest small Poulan this afternoon. All runs were with the stock carb and aircleaner.
Zinger 16x8:
Stock muffler, 6090rpm
Modified stock muffler (baffle plate removed, 5/8 hole in the stock exhaust location), 6480rpm
Open exhaust, 6660rpm
APC 17x6 on the modified muffler got 7020rpm
I've got a g-23 sized V-tech in there from the helicoptering days that I'd like to strap on and see if I can get this thing really cooking!