Which exhaust for an RR4? Currently running a GPR rear can,cat bashed out,but it's just not loud enough! Not much difference to standard on idle,after something with a bit of a rumble!
I've got a RR5 full titanium Micron Serpent system, O2 eliminator but no power commander. Not sure it needs it really. Nice deep rumble at low rpm sound awesome when you let it rip. Quite expensive, hard to find. Only thing that lets it down is the slight angle it sticks out the rear end.