had one after i deleted cat. was too loud straight. it was a very good sounding muffler. mpg gain? i have an auto. not too much maybe 1.5 to 2 at most. but i got sick of it being too tame. i did not have cat intact. just straight pipe with this muffler. i went to a single stack str8 pipe. you want to buy my muffler? :rofI was wanting alittle input on their 4040xl muffler. I know they say you will gain mpg so how much will i gain. And i was wandering how it would sound if i left the cat on. So if someone can give me some info on their experinces with them and maybe some sound clips with a 6-speed, and the cheapest place to buy one. And will this system mount up in place of my factory exhaust?