Thanks marthy, this was an interesting read even though it was based on cars but the principle is the same, Engine - Breather System - Tuning Guides , the idea of having the crank vent to atmos means that there is no oil vapour getting into the air system and ultimately gumming it up (epa laws require no motor gas or fluid is vented to atmos hence laws about blow off valves that are here in sydney and probs other places), I think the two ports you block off and remove the valve is actually an egr (exhaust gas recirculation) system that adds exhaust gas to 'help' with combustion i'm not sure of the benefit i've never had a before and after dyno, ill see if anyone on the sydney riders group on fb have done it and have a shoot out, will be good to get it down on paper, once I get the pcv and run adv gear revb ill take it for a dyno with or without crank vent