Originally Posted by Sh0velMan

It's only positive relative to atmosphere if there is, in fact, substantial blow-by. This engine is not like older examples where there is a mechanism at work pressurizing the crankcase with intake manifold air so that all you need is a single vent, it requires vacuum from the manifold to draw out said air. Without that vacuum, there is no evacuation of the crankcase, as I've said over and over.

And as I addressed in my reply, any true pressure buildup would exit via the breather, so that's a non issue.