Spec vac draw for PCV's?

[Schrade]

Is there a minimum vacuum draw necessary for PCV's to keep crankcase purged?

I want to re-route the PCV purge line IN FRONT OF the air filter, and cap off the plenum PCV port. Get a port fabbed on the AF housing, so that the crankcase air gets filtered BEFORE getting burned.

I ran this idea past Marc, and Dominic, and neither was really impressed by it. one of them said something about having to clean the air filter more often, but that's not something that would be bothersome at all.

The catch can isn't something I'm considering.

When I first finished the 'Top End Resto', and ran half a dozen Closed Loop cycles, I had to break down again while looking for a dropped bolt. Seeing new oil inside the plenum, after cleaning up so much, was dis-appointing.

With grill-work of a sort on the AF housing, the vacuum draw probably wouldn't equate to the same vacuum on the plenum port.

Only question is, would it be ENOUGH vacuum to keep the CC vapors purged???

[mike100]

Marc Haibeck published a mini article that his theory is that it is a ring control issue more than a pcv mist issue. people aren't catching buckets of oil in their catch cans, yet that first qt of oil burns off as windage pretty quickly.

click here

[mike100]

so I just cleaned and sealed the pcv related tubing and concentrated on the throttle body air leak as the issue with idle. There's not much you can do with it outside of possibly restricting the line back to the TB and y-ing off the pcv tubing to atmosphere thru a small filter or something. Outside of that rebuilding the TB.

[Franke]

Schrade, I think you may end up with a little bit of increased crank case pressure too. Similar to when cars used a road draft tube for crankcase vapors and a vented cap on the intake manifold or valve covers. You definitely will have a oily air filter if you duct it before the filter.

[Schrade]

Originally Posted by mike100

so I just cleaned and sealed the pcv related tubing and concentrated on the throttle body air leak as the issue with idle. There's not much you can do with it outside of possibly restricting the line back to the TB and y-ing off the pcv tubing to atmosphere thru a small filter or something. Outside of that rebuilding the TB.

Mike - I'm not sure what you're getting at this post; can you elaborate? (I'm not tying my hesitation investigation to oil fouling)

As far as oil blow-by, Marc and I didn't discuss that, while talking about the oil coming into the plenum at the PCV purge port. He DID acknowledge how much DOES come in there.

Franke - oily air filter? Seems to me that that's much preferred, over fouled intake, valves, plugs, and exhaust...

You HAVE TO agree???

[mike100]

Crankcase pressure is positive when you get on it and manifold vacuum isn't really sucking too hard when the throttle is open 100 percent as it approaches atmospheric pressure.

you could road draft the PCV outlet and the plenum will still get soaked in oil. I wouldn't worry about it. the only thing the pcv circuit does affect is the idle as it is a calibrated leak the system expects to see.

[Franke]

Schrade,
I do agree that it could be a problem if it is excessive. I would then look to the valve seals, rings, breather cover etc if so but I have 56k on my engine and the plugs are clean which tells me I have a good burn on whatever oil is present. I did see a little bit of oil in the plenum past the TB but I don't see a big issue there. My engine doesn't smoke so I don't have a concern. It also wouldn't pass emissions here if it did.
Do you think based on what you saw in your engine that you may have more blow by (oil build up) in the plenum than is normal for this type of engine? Perhaps the oil filters in the cam covers have disintegrated. I think Dyno expressed that in one of his posts when he removed the cam covers. Since some guys on this forum are using oil catch cans I believe the LT5 has a bit more oil consumption than say a standard design engine.
Based on how well your mill is running per your vids I don't see a problem. JMHO.

[A26B]

If you change the vacuum source from the plenum to in front of the air filter housing, you will essentially & effectively kill the PCV system. You won't have a vacuum source anywhere in front of the throttle blades.

Regarding the cam cover filters.
Under normal driving conditions, the air flow is INTO the cam covers, NOT out of the cam covers. The purpose is to allow filtered air into the crankcase, through the cylinder heads so that there will be purge air flow for the PCV system to operate properly.

The filters inside of the cam covers are for high rpm conditions, when vacuum to the PCV is low and there is little to no purge air flow of filtered air into the cylinder head. The purpose of the filter is to prevent splash oil from under the cam covers from getting up & into the aluminum purge air pipes.

If you are really worried about the oil in the plenum, a catch can is the only way to deal with it, simply & efficiently.

[Franke]

Originally Posted by A26B

If you change the vacuum source from the plenum to in front of the air filter housing, you will essentially & effectively kill the PCV system. You won't have a vacuum source anywhere in front of the throttle blades.

Regarding the cam cover filters.
Under normal driving conditions, the air flow is INTO the cam covers, NOT out of the cam covers. The purpose is to allow filtered air into the crankcase, through the cylinder heads so that there will be purge air flow for the PCV system to operate properly.

The filters inside of the cam covers are for high rpm conditions, when vacuum to the PCV is low and there is little to no purge air flow of filtered air into the cylinder head. The purpose of the filter is to prevent splash oil from under the cam covers from getting up & into the aluminum purge air pipes.

If you are really worried about the oil in the plenum, a catch can is the only way to deal with it, simply & efficiently.

You are correct sir about the filters. I stand corrected. what was I thinkin?

[Schrade]

That sheds light on the PCV system SOURCE air there Mr. J; also explains why the cam cover pipes were clean on the inside BEFORE Top End breakdown in Nov...

Still wondering here if there's improvement possible...........

??? The PCV-to-plenum inlet is RIGHT UNDER the TB primary butterfly???

Hmmm...