MyE28.com

M635CSi wrote: I'm not sure it's such a good term to use but I meant to convey the effect the pumping action of the pistons have on the crankcase/valve cover vents, a pressure pulse is evident when the vent is open to the atmosphere.

I think that pulse that you may feel is actually blow-by. On a multi-cylinder engine with equal degree separation of the crank journals the crank case volume will remain static.
As far as the oil goes, in what ever form you prefer, aerosol is perhaps most fitting though I haven't actually analyzed the stuff, the fact is that it gets past the baffles in the valve cover and coats the intake tract unless it is dealt with by another devise.

wjones wrote:
Mmm. Food for thought.

There was a recent thread on anothor forum where they were talking about using the exhaust for vacuum and plumbing the vent into there (using a check/arrestor valve). I have no idea how that might affect the cat(s).

This technique is used in some applications in motorsports. I don't think a catalytic converter would enjoy it much though.

Sweeney wrote:

M635CSi wrote: I'm not sure it's such a good term to use but I meant to convey the effect the pumping action of the pistons have on the crankcase/valve cover vents, a pressure pulse is evident when the vent is open to the atmosphere.

Sweeney wrote:I think that pulse that you may feel is actually blow-by. On a multi-cylinder engine with equal degree separation of the crank journals the crank case volume will remain static.

Blow-by is the larger component that can be seen sometimes violently at the vent. If we think of the space directly beneath the cylinder as the "crankcase" it is easy to see that as the piston travels, the pressure and volume in the "crankcase" changes (is not static). As these "crankcase" pressures and volumes change with piston movement they cancel out the positive and negative pressure waves in adjacent "crankcases" (blow-by no withstanding) and between other cylinders. So while the larger crankcase volume remains static the individual “crankcase’” volumes and pressures do not, nor does the larger crankcase pressure. Blow-by amplifies this effect.

Sweeney wrote:As far as the oil goes, in what ever form you prefer, aerosol is perhaps most fitting though I haven't actually analyzed the stuff, the fact is that it gets past the baffles in the valve cover and coats the intake tract unless it is dealt with by another devise.

I understand there is a small centrifugal oil separator available that can be fit to the valve cover. Sounds like it would be particularly good for use in a turbocharged engine. The oil is caused to drains back into the engine and only oil vapor passes to the intake.