db944

Can anyone tell me if the "valve" in the pic below is a PCV valve on our cars? If so, what is the implication of running without it? For example, if one were to install an open breather catch can like Lindsey racing sells? More crankcase pressure or less?

Claus Groth

I've parted several turbos and an S2, none of which had a valve there. All had a 90 degree hose at the top of the A/O separator. Which car is it listed for?

Chris Prack

No it's not. That valve is there to release positive pressure in the crankcase. The oil/air seperator acts as a pcv of sorts in our cars. There is no actual valve.

db944

This is on an '89 turbo. Chris, isn't that what a PCV valve is? "Positive Crankcase Ventilation?"

Chris Prack

Yes, you are correct but Porsche did not install one on the 951 in any year. The early cars had a fixed orafice and a restrictor but the later cars they did away with them.

PCV systems on cars that use an actual valve have engine vacuum on one side of a check valve with a metered orafice that is in the crankcase or intake of the engine. Porsche only used one on some 911's in the 80's.

Dal Heger

I have never seen that valve, nor that rubber elbow on any cars. That line goes from the air oil separator to the intake right in front of the turbo. It should never see pressure. What does the other side of that "valve" hook into?

These cars don't have a PCV valve, the crankcase is typically under a little bit of vacuum the whole time the cars are running.

Dal.

kevincnc

The 90 degree hose hooks to the top of the OAS, the other end goes into the j-boot just before the turbo, and the valve vents positive pressure to the atmospphere.

Edit: I should have said that it would vent postitive pressure if there were any pressure there. When the engine is running, there should only be vacuum in the j-boot, right?

Dal Heger

That's my point, there should never be a need for a valve to vent positive pressure at that point because there will never be positive pressure at that point.

My question still stands, what does the other end of that valve connect to? It wouldn't pass emissions if it vented to atmosphere, even a visual check. It has to be connected to something.

Dal.

Chris Prack

The valve is vented to atmosphere. Any pressure would have to overcome a spring on the valve to release the pressure. So in the absence of pressure the valve is closed.

db944

Chris is correct. The valve vents to atmosphere. The diagram is the Porsche parts diagram. When you remove the intake manifold on the '89 944 turbo, this hose, with valve, is displayed just like the diagram. I guess this is one of the changes made with the increased horsepower of '88 Turbo S and '89 turbo (the M44.52 engine).

Thom

Bump... and some contradictions posted above.

Does this valve open :
- when there is pressure in the AOS line
or
- when there is vacuum in the AOS line?

Oddjob

Will open if there is excessive pressure in the case/breather.

Thom

Thanks Jim - any idea at what pressure it should open?

Thom

Bump.

What is the maximum tolerable pressure in the crankcase?

zerMATT951

Could it be a safety device to prevent blowing seals out if excessive blow-by caused significant positive pressure in the crankcase?