If all your going to do is throw on a muffler without anything else you are not going to save that much in MPG, it will probably not be that noticeable. It will help a little but how much just depends on the factors. Just like your mpg can vary from fill up to fill up so too can the affects of a muffler differ from day to day. It has a lot to do with your driving habits. If your looking for real MPG gains your best bet is a full catback system, improved driving habbits, and a CAI. As for the sound I Had a flomaster on my cavalier (same motor) and it sounded good I am sure the magna flow would sound good too.