The longer MAgnaFlow mufflers are very quiet. Wen we did dyno testing of mufflers and found that the Maganflow mufflers also increased some HP. When we put the Flowmasters on we lost HP. They just do a beter job of marketing. Last year I called Flowmaster to get the CFM rating on their mufflers and they told me "that they don't rate them that way", I am not sure what other way would be relevant. Maybe they have changed since, but I have never checked. Tom Hand wrote a book on building Pontiac's for the street and strip. Great book. He also tested 54 different mufflers on the flow bench, engine stand (with professional noise measurements) and at the drag strip. He found the Flowmasters one of the least desirable mufflers available. Kinda backs up my experience on the dyno.
