[Ant]

I think anything that can easily alter the sound of the exhaust is illegal in a lot of countries. We have found that you can be really noisey but if driven quietly by a mature person, there is no problem in NZ. I am using 3' perf tube race mufflers and will interchange with a series of smaller perf tubes, there is some fancy material available for this which I am researching!

Another better alternative maybe using what the new Corvettes use a responsive exhaust the faster you go the less back pressure, I think they have a butterfly/valve setup in the rear mufflers, so when driving slowly its relatively quiet?