Oil Pressure ?

[Maj]

Yes the pair to crank breather mod is common, reduces air pressure in the cases and therefore windage losses are less , total performance oriented bikes like pro stock drag bikes run a vac pump to gain hp, and it must have a fair difference or they would not add the weight of the pump

same sort of reason i cut the bottom of the cyls to match the case cutouts , provides a short path for the air under one piston moving down rapidly and compressing the air to travel to the next rising rapidly creating a low pressure , both costing hp if they were not complimenting each other , creating a vaccuum or lower pressure within the cases means less air to pump around & reduces these parasitic hp losses

used the marble a few times Greeny :) works wonders to stop backfires in aftermarket exhausts