Purely anecdotally I used to have a motorcycle that after about a year had the muffler need replacement. I was a poor student and so bought a fake one instead that was just a muffler shaped pipe.
The difference was immediate and extremely noticable, the number of near misses went down a huge amount and the few times people got a little close I could just chuck the clutch in and give it a good rev to scare anyone off.
My biking days are done for now but if I go back I will not be going back quietly.