PCV System

[Howieau]

Hey,

I'm confused with how the PCV system works. I understand it all, but the part I don't understand is shown on the following diagram.



It shows air going into the valve cover via the hose connected to the intake pipe. I don't understand how this is so? Isn't there always vacuum in the intake pipe, so wouldn't blowby be sucked out from the crankcase into the intake pipe.

I have seen a few diagrams show the same thing and cannot understand how it is supposed to work that way.

Cheers

[Roundy]

Air pressure will pretty much always be higher in front of the throttle body as the throttle body (more specifically the throttle plate) poses a restriction even at 100% throttle, so in that diagram i can see how it would work

on a turbo engine, i don't know how it would work posted exactly like that tho, because the pressure will be lower before the turbo than after the throttle body...

[Howieau]

Yeh I understand now. I think in a turbo system the PCV will close under boost?

[Roundy]

i don't think it does, it might work in the opposite direction on a turbo car?

The PCV on the GT4 comes in before the turbo, hence the nice covering of oil over the compressor blades and through the intercooler

[MWP]

When you are cruising/idling, there is vac in the inlet manifold.
This vac draws air through the PCV valve from the sump.
That air being pulled out need to be replaced, so fresh air is supplied by the pipe to before the TB.

Basically, PCV keeps fresh air in the crankcase (slows down oil contamination from blow-by gasses) and put a very slight vacuum in the crankcase which helps stop oil leaks.