A lot of discussion in this forum talking about selection of mufler to improve the performace of an engine.

Honestly I got confused.

Because I though we need a mufler nothing more than to keep the noise down. But now I am sure that it does much more than that.

Please allow me to ask these questions :
1. How does mufler work to achieve top performance of an engine ?
2. What are the selection criteria to find a good mufler ?

Thanks a lot [8D]