Sorry, Zeke. By trial and error (and looking at the way the old RSR's and RS's would block off their sport muffler outlets) I discovered that the overall volume of the muffler would go down sigificantly by capping one of the two outlets. Obviously, if the two headers didn't lead into a common chamber, this would be an engine-destroying idea.
Reducing the size of each side would probably have a similar effect, but the fact that Flowmaster makes the same muffler with single and dual outlets suggests it's safe, and it's very simple to pop the soup can on or off.
