Found this in a chat room, and found another article, that said the original AAR side exhaust mufflers were restrictive, only flowing 175 cfm.
"Besides the mufflers I make, I do like the Stainless Ultra Flows. I'll be running a set of prototype stainless Super Turbos we built while I worked for Dynomax 11 years ago. These are reverse flow to go on my AAR. We flow tested an NOS muffler I have for the AAR-T/A & it tested at 175 sCFM. The ones we built for my AAR flow 375 sCFM. I can't wait to hear them!"
Something about a "pinch down" area on the muffler, that restricts flow.
I think the Walker Super Turbos flow up near and above 400 CFM. TTI recommends them, due to high
flow and lower noise. But on my 3 inch system, I still wear earplugs. The X pipe seem to make
it quieter.