I've looked into this question - theres a lot of info on the .net site - I concluded that unless your using the bike for racing (constant high revs), they don't work well at lower/middle rev range. If you are using the bike on the road (like I will be), with the cr replica exhausts fitted, you won't be riding at constant high revs - have a listen to the sound level at high revs and you will see why I say that - great sound but not for too long!