I installed a Magnaflow muffler on my 2012 RT S in June. I now have about 2000 miles since the install. On a trip through Idaho, Montana, Wyoming and Utah I got a high of 42 Mpg and a low of 25 Mpg. Average for the trip was 31 Mpg. Since returning home the last three fill ups mileage has been between 37 and 39 Mpg. The low fuel light has been coming on around 200 miles on the tank. I have been using gas with no methanol. I am very happy with the mileage.