[sambo]

Some great wisdom/insight there from all - thanks. I guess down here in Melbourne, Australia, when putting a new Cobra on the road we would all like "live" side pipes but they don't meet noise restrictions. So these cutouts will allow us to silence the pipes when needed, and with the flick of a switch, direct the flow to the side pipes.

It would seem that a lot of thought needs to be given to the placement of the cutouts, in order to maintain the low end torque and high end flow? Eg, an experienced exhaust guru who knows a bit about your particular engine setup and what works best.