I agree with Bruce. I have been using the AR exhaust system and wanted to try boring out the stock exhaust because the AR is so loud. After boring out the front two baffles in each muffler i tried it. Not a big difference in performance to the AR system. There are two baffles at the rear of each muffler that appear to have 5/16” diameter holes in them. In the very rear plate i bored them to 3/8” and the performance is good and just slightly less noisy than the AR pipes. The exit of the standard pipes is further behind the ear which is a good idea.
