The next myth has to do with performance mufflers. Performance mufflers are not just for kids, they can improve many aspects of a car. These include power and the gas mileage a car gets. By letting an engine work easier with a larger exhaust pipe and performance muffler, overall performance is acquired. Decreased engine temperatures are also a side benefit. Of course there is also a louder sound as well.
http://www.autosupportforum.com/general/10-biggest-automotive-myths/
