PCV during boost

[ciscokid]

I'm trying to understand how the crankcase gets ventilated when the engine is on boost. It looks to me like the PCV valve is pushed closed with positive manifold pressure. So, what becomes of the crankcase pressure due to blow-by, which is likely to be at it's peak under boost? It's hard to believe that the crankcase pressure could, or would, overcome the positive pressure on the top of the PCV valve. It seems like the only outlet is the breather at the back of the valve cover, and that would pump crankcase vapors into the intake air stream pre-turbo.

[svono50]

You pretty much nailed it on the head. Under boost, all crankcase pressure is vented through the valve cover oil separator system that leads down into the turbo inlet. When you are at part throttle (i.e.- no boost) the higher of the vacuum signals (PCV/valve cover) will pull the fumes/pressure from the crankcase. If your PCV valve doesn't seal under boost, you will get excessive crankcase pressure do to intake pressure 'helping' things along.

Unfortunately that oil separator on top of the valve cover doesn't always remove all the oil and you end up getting a coating on the intake tract...which isn't good for the engine as oil can cause pre-ignition detonation if enough is present. My own car has always pushed enough to fully soak my intercooler core, which I had to flush out on a yearly basis till I added a secondary oil separator that I mount behind my charcoal canister to trap all excess oil. Since then my intake has stayed nice and dry and I simply replace my secondary filter element once a year in the spring.

[Johnnym]

I kept having oil leaks and such. So I done away with my PCV valve and run a -16 hose to a catch can. I have no vacuum assist just atmoshericly venting it. I also vent my valve cover to atmosphere. Of course I have no more oil in intake track and now I have zero oil leaks.

[svono50]

I kept having oil leaks and such. So I done away with my PCV valve and run a -16 hose to a catch can. I have no vacuum assist just atmoshericly venting it. I also vent my valve cover to atmosphere. Of course I have no more oil in intake track and now I have zero oil leaks.

That is certainly an option and done properly as well. A lot of folks simply 'dump' the valve cover to atmosphere, but leave the PCV line connected to the intake. That air that goes into the crankcase from the intake is metered air, but it vents to atmosphere, which is like having a vacuum leak and will cause idling issues. If you vent to atmosphere, it has to be on both ends...good move!

[Johnnym]

I should have added that I am running an aftermarket engine management also and yes it should be on both ends if not.