Keith, as a courtesy to you and others that are curious, I took a quick pic of the stock Superformance muffler. I've also gone ahead and reposted a previous pic on page 1 of this thread so that you can see the difference.
Factory Superformance muffler - 2" perforated I.D. with steel wool as a packing material:
Stainless Specialties custome muffler - 3" perforated I.D. with ceramic matting as a packing material:
A better view with a baseball rolling down the center.
Hope this helps!
-Dean