crankcase ventilation

[zaq123]

Also related question regarding How crankcase ventilation is designed on M20. Ok so there is a drain tube between the head and the crankcase as well as oil drain holes near cam rockers in the head. Valve cover has only one line routed right before a throttle plate. Correct me if I misunderstand the design:
1. Unlike in typical PCV design, the crankcase is not under vacuum (typically a vac. line from somewhere after TB) and it has no fresh air intake (typically the air box)
2. Crankcase venting is sealed to the engine and valve cover vent is just vent fumes
3. There is no vacuum in the system. There reason why folks report idle changes when removing oil fill cap because any air inlet created after stock AFM affects AFM door opening? For example if one plugs TB valve cover vent port and drops the hose from the valve cover vent to open air, no more idle changes on stock m20?

[zaq123]

any comments on this? There is no vacuum in the crankcase on M20 because it wants before throttle plate? Am I correct?

[digger]

there is should be only a very small amount of vacuum as it is pre throttle body so just whatever the upstream system creates which is very small.

[zaq123]

Im in the process of rigging up the oil separator from S62 p/n 11151406789. Basically want to make similar arrangement to S14 oil separator where its going to vent into the back of ITB airbox and drain into the dipstick tube. That oil separator will be plugged in to the airbox via grommet to minimize on running vent lines, similar how S62 has it mounted. Just need to hot steam shape the hose from the valve cover. Just want to make somewhat maintenance free system where one doesn't have to keep an eye on the catch can

[zaq123]

here is what I came up with. I didn't want to braze the oil return line on the dipstick tube as it would require painting the whole thing. Also Didn't want to separate the dipstick tube 325iX style with rubber hose and clamps as I wanted more rigid setup. -10AN 37' flared fitting did the job plus it lets change the angle of the dipstick tube as one needs it to be.
Had to bend 3/4 ID Gates hose (p/n 28478) with a steam and spring mandrel for a kink free routing around fuel rail, inj. harness and all those things. Basically hot steam through the hose with subsequent cooling in the bucket of cold water.
Also OEM dipstick tube is not exactly 5/8 to fit snuggly in the flaring tool so a couple of thin wall (0.016" wall) pieces of 5/8 aluminium tubing did the trick as it fits nice and snug around e30 dipstick tube for true 5/8 diameter.

Here is the result. Still need to get 90 degree AN to hose barb adaptor for the drain hose but you get an idea. Oil separator will be attached to the back of the airbox between runners 3 and 4 via grommet. 21mm ID x 2.5mm groove grommet works perfect with S62 oil separator and the aluminium Airbox backplate.