Dont know what you mean...the air box is just a convenient place to vent the crankcases to. Some people just put a filter on there and vent it to the atmosphere.. the reason there is a one way valve there when it is connected to the airbox is to stop airbox pressure (which is significantly higher) blowing up the crankcases .
I always thought the NR valve was to maintain a slight vacuum in the crankcase to reduce pumping loss? Can stand to be corrected though....
Underside of the pistons pumping up and down create a pressure .. if this can be removed then it’s less resistance for said engine so it goes via a pipe to somewhere more often than not the air box When you are flying down the road the air box is filling with air .. under pressure you don’t want that going into the crankcases hence the one way valve
