i have made the one end 9mm because the catch tank that i am using has the same diameter zo i could use 1 hose nicely
the surface of hole in the valvecover + the surface of the hole in my part is more then enough combined, to assure that there is no pressure building up, in a short way, the ventilation works properly, bigger is possible but why??? in this way i could use simple hoses and i did nt have to use any NPT fittings or what so ever.
once again
it is correct that when the original breatherchamber is connected to the intake manifold the oil fumes are burned, but that is exactly why i have designed this part! I DO NOT want to burn the oil fumes because i want to keep my combustion as pure as possible to get the best bang! plus the nice advantage u get for free is that your internal parts stay clean (at least throttleboy, intakemanifold, injectors etc)
in your combustion you only want fuel and air, not fuel air and oil. the only reason honda did this from stock is because of enviormental aspects, but when u use a catch tank it should be ok.