are you guys gaining any milage when installing magnaflow cat back systems on your 4.6and 5.4s

 

No mileage difference here. But it sure sounds nice!!!

 

I actually gained .4 MPG by using a magnaflow flowthru on the stock system. Just had the factory muff taken off and put on a Magnaflow # 12245 and kept the stock tailpipe. Had to add a 16" piece to make up for the factory muffler length. Total cost was $215.00. The factory muffler weighs about 75 lbs so the weight alone will help.