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Thread: Crank Case Ventilation fully explained. (Naturally aspirated edition.)

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Posts: 121-130 of 165
2011-07-30 03:28:06
Awesome! Congrats Ben!
2011-08-01 07:33:59
Originally Posted by BenFenner
SR20_Guy, sorry for the late reply. It depends on how often you're going to run the vacuum pump. If you are running the pump only at WOT or high throttle positions then you still need the PCV line. If you're going to run the pump all the time (assuming it can handle continuous running and you can put up with the noise) then you don't need the PCV line anymore.

Thanks Ben,

I think I may opt for the exhaust scavenging setup instead, as finding a suitable pump seems to be a problem.

Does your answer remain the same for this setup?

I have pulled the hosing off the top breather outlet - the one that usually leads to the Intake pipe - and it builds some serious vacuum there at idle. If I hold my finger over it for a few seconds it starts sucking on it pretty hard. When I let off it sounds like a dumpvalve! I figured the vacuum must be originating from the small tube connecting the intake manifold to the VC (near the middle of the intake cam side of the VC). I pulled that tube out and sure enough, the vacuum went away.

My thinking is that if I run the exhaust vac system then I can't have the motor trying to suck vacuum from that system (even though the pcv valve will block it sucking exhaust air back up), it just doesn't seem right ot me.

So I'm thinking I need to pull that small tube form the intake and block off both the intake and VC where it would usually go. It will cause some issues with idling but I should be able to adjust the TB to correct for it.

Would like to hear some thoughts please.
2011-08-01 12:04:16
You still need the smaller PCV hose hooked up. The one-way check valve stops any exhaust from entering the crankcase in the rare moments there would be positive pressure there.

When plumbing the exhaust venturi pipe, don't forget it is best to have it after the catalytic converter if you have one.
2011-08-01 12:46:56
Cool I get that it won't be able to suck anything in via the exhaust due to the checkvalve. What I'm wondering is what will it do with this vacuum instead? What/where else will it build up this vacuum if it can't get the air form the passage it previously got it from?

Also thinking about guys running ITB's. What is happening to their motor in the absense of this line between the IM and the VC?
2011-08-01 12:54:55
The engine doesn't really need any air through the passage ways. One of the benefits of the exhaust Venturi method is that the crankcase is basically a sealed unit at that point. This increases vacuum in the crankcase at idle (make sure that restrictor is there!). With no way for air to get into the crankcase from the outside, the vacuum will be stronger at idle and partial throttle. And from partial throttle to WOT you will see anywhere from 0.5 psi to 2.0 psi pressure drop across the exhaust Venturi pipe.
Last edited by BenFenner on 2011-08-01 at 13-02-26.
2011-08-01 13:02:37
Thanks that makes sense.

Now lastly, just cause I want to understand this - what will the downside be to removing that hose between IM and VC?
2011-08-01 13:05:29
The bigger hose? No down side really in rerouting it to the exhaust (that's what you meant by removing it?). Not that I can think of.

The smaller hose should not be removed. Even with the exhaust Venturi hooked up, you won't see any real vacuum in the crankcase at idle and only a little bit at partial throttle. You'll have lost the vacuum in the low load situations. Blow-by will increase at idle and ring seal will suffer. That would be the downside of removing that hose. It would be a really crappy situation at stop lights and such.
2011-11-27 19:59:37
Still no more oil burning in my VE months later after getting the PCV system back into shape. Used to go through about a quart between changes.
2012-01-16 03:34:08
which of the newer 2000+ valve covers will fit on a DET head?

I want to get rid of my oem catch can.
2012-01-16 05:27:33
Originally Posted by unijabnx2000
which of the newer 2000+ valve covers will fit on a DET head?

I want to get rid of my oem catch can.

VE only.

RR one sits too low and will hit the oil squirters.
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