Crankcase Ventilation

[Formeister@domain.elided]

I have a question concerning positive crankcase ventilation.  Spica equipped
engines get their idle air from the crankcase breather as do factory equipped
carbed engines effectively putting the crankcase under a negative pressure -
especially at high manifold vacuum such as closed throttle positions going
down hills.  Some after market filters, ITG for one, does not have this
provision and I'm concerned that oil in the cam galleries can't effectively
drain from under the tappets if this area is under pressure, possibly leading
to oil being forced down the valve guides or worse blowing out a front or rear
crankcase seal.  I currently have two K & N breathers, one on the back of the
block and the other on the cam cover vented to the atmoshere.  Am I being
overly cautious?  Has any one ever measured crankcase pressure at idle and at
full load?  I realize ring blow by will increase this pressure but what's
normal?

Regards,

Frank Formeister

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