I have the Flowmaster 40 Series and I really like the sound it gave my Jeep. It is a lot louder than the stock muffler but it gives a deeper more aggressive sound. I kept everything the same on mine except for the muffler. I just welded it in using the original pipes because they were still good. I know that you will read that you will get more horsepower and better gas mileage, but I did not see a change in either of those things. You should look on youtube and do a search for Jeeps with the Flowmaster Super 40 to find out how it will sound.