Everyone knows that mandrel bent exhaust is less restrictive than press bent but in searching the forums I couldn't find any hard numbers. Usually when you get before and after results, the muffler was also changed out. I did some googling and came across the site below where they did dyno on the same vehicle and muffler with just the pipes changed out. Some of the numbers are impressive but the first are rather ho hum. Does anyone else know of some more hard and fast numbers? The reason for the research is that I have seen some cat back installs that didn't seem to make much if any more power than a much cheaper muffler upgrade. I intend to go with a full cat back but I was just wondering how much I was actually gaining for the extra $$$.

http://www.bobsmuffler.com/dyno.htm