Official catch can/crank case vent system thread
the pressure in the manifold is whatever the gauge reads. as the TB opens it equalizes the pressure in the manifold ~19"Hg. against atmospheric pressure (14.71 psia, this is absolute pressure)
Helen keller was never lost
Last edited by mrbelvedere; Nov 7, 2013 at 11:40 AM. Reason: Automerged Doublepost
SMH. It has been explained to you over and over; Technical information posted. Laws of physics explained. Hard to do more than that.
One question at a time.
The hose on the back of the vc is connected to the intake tube, which is at atmospheric pressure.
The intake manifold is (let's say at cruise) has a vac of 10" as read on the gauge.
The gauge is telling you that the absolute pressure in the IM is 10" below atmospheric
So, how is the crankcase pressure (by your logic) lower than the intake manifold?
This may be the most correct statement you've made regarding pcv yet.
Yes atmospheric pressure replaces vac.
The manifold pulls a vac on the crankcase (any time your boost gauge reads vac greater than 3kpa, less than 1/2"hg)
This vac is replaced by fresh metered atmospheric air supplied by the rear pcv tube running to the intake tube.
Last edited by armcclure; Nov 7, 2013 at 02:29 PM.
Ok lets move forward here I just would rather not participate than continue to deal with Mr. B to tell the truth. So whatever JW you post about this particular subject, I promise not to reply.
I really hope you're joking... Or enjoy popping dipsticks.
FYI turbo swaps using the Saab IM retain identical pcv operation as stock, other than the FAI being unmetered on a blow through setup.
FYI turbo swaps using the Saab IM retain identical pcv operation as stock, other than the FAI being unmetered on a blow through setup.
I still don't see where you're finding this magical pressure that defies physics and closes the valve..
I believe it stems from the fact that you (incorrectly) still believe the fresh air inlet is the pcv's primary vac source. It is not. It is a fresh air inlet and the relief passage for blowby gasses when the valve is closed.
FLOW has nothing to do with when the valve opens/closes. It's PRESSURE. one side of the valve is connected to the post tb vac side of the IM. The other is connected to the case/FAI/intake tube (near zero pressure ie atmospheric)
AT ANY TIME THAT MANIFOLD VAC IS MORE THAN 2-3kpa GREATER THAN ATMOSPHERIC PRESSURE THE VALVE IS OPEN.
This is not my "opinion" it is a ******* FACT.
Either way, I have a guy coming over tonight allowing me to run a test on his car, to prove to you once and for all that the valve is open at cruise.
I believe it stems from the fact that you (incorrectly) still believe the fresh air inlet is the pcv's primary vac source. It is not. It is a fresh air inlet and the relief passage for blowby gasses when the valve is closed.
FLOW has nothing to do with when the valve opens/closes. It's PRESSURE. one side of the valve is connected to the post tb vac side of the IM. The other is connected to the case/FAI/intake tube (near zero pressure ie atmospheric)
AT ANY TIME THAT MANIFOLD VAC IS MORE THAN 2-3kpa GREATER THAN ATMOSPHERIC PRESSURE THE VALVE IS OPEN.
This is not my "opinion" it is a ******* FACT.
Either way, I have a guy coming over tonight allowing me to run a test on his car, to prove to you once and for all that the valve is open at cruise.
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From: modesto
On a healthy engine that is very true but how many of these guys running around here have hurt engines? My Gess is majority. Were blow by overwhelmes the stock pcv system.
So you're claiming that the crankcase (which is open to atmosphere via the pcv tube), at cruising speed, is somehow creating a vacuum (out of nowhere) that is stronger than manifold vac?