Valved or not – whats the difference…

Didnt plan on fitting an after-market system but I’m now a little more interested having heard a few systems in the flesh.

Not interested in a Non-resonated system cos I prefer a more suble exhaust note but I notice most exhausts come in 4 options –

The aformentioned non-resonated with Valve, non resonated valveless and then Resonated with valve and valveless.

So the question is simple – what is the difference between the two apart from the exhaust flap (that I currently have disabled on mine with the mod most of us done) apart from the price?  Anything significant I need to know?

cheers…

Just to add – I’ve been looking closely at both Cobra and Scorpion systems which seem to offer great value for money over the Mountune/Milltek systems…