Blow by

[Oilgal]

Gary, BuickGN and 7055

I hope you guys don't mind me taking advantage and asking you this.

Going by the picture of my PCV setup, do you think I am getting enough venturi effect on the PCV hose routed to my aftermarket air cleaner assembly to afford adequate cross-flow ventilation, at higher rpm when manifold vacuum is low?

Maybe I don't understand how the system works yet, but it appears that cross ventilation flow is meant to reverse at higher rpm. Have I got this all thoroughly misunderstood?

 

[Oilgal]

Wait a minute. I don't see how it could reverse cross-flow now come to think of it.

Sorry for butting in. sigh

I wish I could find a good comprehensive write up the PCV system.

 

[Gary Allan]

Quote:
The whole point I'm trying to make here is the vacuum helps ventilate the crankcase,


..and I totally agree

Quote:
and its more important on turbo cars.


Well, it's in pretty short supply ..but we'll say that a differential is helpful.


Quote:
I'm not sure where we're are going


..trying to figure this out, myself. I thought you were saying "follow me here".

my take-

Most turbo installations that I've seen, most of them being OEM, what would be considered excessive for a NA engine is considered normal for a turbo due to the lack of effective draft in the presence of boost.

 

[7055]

Originally Posted By: Gary Allan

Quote:
I'm not sure where we're are going


..trying to figure this out, myself. I thought you were saying "follow me here".

I was dissagreeing with two points, one was that vacuum isn't needed and the other was that PCV is only for emmisions.

 

[7055]

You know theres everybit as much vacuum on a turbo car as there is on a N/A car.

 

[Dyoel182]

At certain times sure.

 

[Big Jim]

Originally Posted By: 7055
You know theres everybit as much vacuum on a turbo car as there is on a N/A car.


Up until the vacuum turns negative due to boost.

Better said, negative pressure (vacuum) becomes positive pressure under boost.

 

[Junior]

Originally Posted By: 7055
Originally Posted By: Gary Allan

Quote:
I'm not sure where we're are going


..trying to figure this out, myself. I thought you were saying "follow me here".

I was dissagreeing with two points, one was that vacuum isn't needed and the other was that PCV is only for emmisions.


Ok, I think we kind of agree. Crankcase vent to vacuum helps.

However, at WOT with a NA engine, the blow-by is most likely going to overwhelm the PCV due to low vacuum in the intake at WOT.

We have thousands of offroad diesel engines running at 25-30psi of boost with only a crankcase vent (no vacuum)with 300 hour OCI. Now with the advent of tier 4 we have to run all this blow-by back into the inlet side of the turbo. Hence my opinion this it is emmisions driven.

 

[Junior]

To your point though, if it were emissions only, then NASCAR wouldn't vent to exhaust using the venturi affect to draw the blow-by out of the crankcase.

 

[7055]

Good points, I've already learned quite a bit at this forum

Originally Posted By: Oilgal
Wait a minute. I don't see how it could reverse cross-flow now come to think of it.

Sorry for butting in. sigh

I wish I could find a good comprehensive write up the PCV system.


This might help, I don't know what you mean by crossflow

http://www.filtercouncil.org/techdata/tsbs/94-2R1.pdf

 

[Oilgal]

Thanks 7055. I have yet to see any PCV system write ups that go past what that one covers.

I have long wondered if the venturi effect on my custom setup, at the connection of the rear valve cover vent to my air filter box, would at WOT reverse the usual flow of crankcase ventilation.

The usual flow is back to front, as air vented in from the back valve cover vent is pulled through the block to the front valve cover by manifold vacuum through the PCV valve in the lower intake, which is connected to that front valve cover.

So what I am wondering, specifically, is this.

Since at WOT the manifold vacuum at the PCV valve is low or absent, will the venturi effect at the filter box end of the crankcase ventilation system, reverse that usual flow and adequately evacuate crankcase gases at WOT? Man I hope I made sense that time.

Below is a picture of my custom setup. Just click to enlarge it. Would you be so kind, as to please take a look, and then tell me if my above assumption is true?



My air filter draws air in through this router in the hood. click to enlarge



Which is connected to the reverse cowl on the hood. click to enlarge



I just want to make sure I have my PCV system right. That's why I am asking you guys.

Thank you all very much.

 

[Oilgal]

Oh dear. I just realized how stupidly big my last post is.

I know your cars are probably waaaaay better than my stupid van is. So I am definitely not even trying to show off. My rig is just me tinkering as I have begun to learn about these things, and obviously I have a low budget.

I hope you all understand, and I hope you will educate me by answering that question I asked. I just really need to know.

Thanks again. I will try to keep out of your discussions and just read now.

 

[vacuum_6]

Originally Posted By: Oilgal

If you have a central tube (the modded PCV valve I recommended), connected to where that little filter screws in, which extends three fourths of the way down into the reservoir, 'and' you make certain that the CC ventilation gases flow from the engine to the catch can 'and' down through that same central tube ..... so the gasses must then turn and flow back up to the top of the catch can .... to then exit through the other port at the top of the catch can , the oil vapor, (in addition to some percentage at least of whatever micro particulate exists) will be separated by inertia, surface adhesion and gravity, .... and probably some other "stuff" I haven't thought of too.

So anyway there is more than just gravity involved. You must make certain, that you install the catch can in the way outlined above, or it wont work worth a (rhymes with) bam.

The method you speak of, means that at most you will be relying on that tiny plastic filter alone, which will also break down from heat 'and' exposer to the corrosive CC gases being ventilated.

If it helps, I didn't think of all this stuff.

I was schooled on this by a friend of mine, who is a whiz bang engine builder and custom fabricator, who has had his work featured in just about every (rhymes with) bam Hot Rod and Car Magazine you can think of, including Hot Rod Magazine. I am just a dumb old lady OK?

From what you are saying and if I understand correctly, the incoming catch can path should extend down to the bottom due to physics of things. This allows the "stuff" in the air to be filter out before exiting the can. Right?

 

[Oilgal]

Originally Posted By: vacuum_6


From what you are saying and if I understand correctly, the incoming catch can path should extend down to the bottom due to physics of things. This allows the "stuff" in the air to be filter out before exiting the can. Right?


Yes. But it allows the "stuff" in the air, to fall out of the air stream, which is slowed down by the sudden increase of volume within the path, that is the catch can in question.

Maybe I am wrong, but I believe that the close proximity of the incoming and exit ports, within the air drill water separator based catch can, would make it far less efficient without that central post extending down. I think it best however, to only extend that central post about 3/4 of the way down into the reservoir. I may be wrong about that too though.

The more I learn here the more I realize just how little I know. I learned many things that are just plain wrong, I begin to realize, and I am really trying to unlearn and relearn here. So please do correct me if I am wrong about something.

Also, I try to be concise, but I know I am not real good at that.

Thank you for your patience.

 

[vacuum_6]

Originally Posted By: Oilgal

From the picture (it's hard to tell) does the inlet tube stop at the top of the SS mesh then starts again at the bottom of the mesh.

 

[Dyoel182]

The tube goes all the way down so the air is forced to hit the bottom and come up the sides through the mesh.

 

[yeti]

i made a catch can last winter, as i have a lot of short trips, and the oil does not get hot enough to burn off contaminants. the 'can' is the typical compressor filter/ separator bottle. there was a white porous filter that i removed, as it worked better without it. the tube only drops about 3/8" into the bottle. the oil and water vapors condense and collect at the bottom. i used 2 pieces of gas line hose,about 10" each. one from the pcv valve to the bottle fitting, and the other from the bottle fitting the to the male fitting on the intake. the bottle fittings are barbed 90 degree nylon. the bottle hangs a little below the level of the pcv valve,and i have it supported near the master cylinder by a couple of cable ties. after about an inch of fluid collects, or before a highway run, i unscrew the bottle from the top of the assembly and dump it. it works very well.

 

[Oilgal]

Originally Posted By: vacuum_6

From the picture (it's hard to tell) does the inlet tube stop at the top of the SS mesh then starts again at the bottom of the mesh.


The tube passes through the mesh.

I screwed an old PCV valve for Mitsu 3.0, in place of the filter that comes with the air drill separator, and it fit like a glove. Just be sure to cut off the PCV tube where it begins to narrow, and remove the one way valve and spring inside.

 

[vacuum_6]

Thanks for the 411. For the mesh, what type of steel wool is used?

 

[Oilgal]

Myself I don't use any mesh at all vacuum_6, and I really don't know what would be OK or best to use either. My builder friend said I didn't need any mesh, in that little catch can on my NA V6, and he strongly advised me against just putting some steel wool in there. I would be very careful about what you decide on this. Even though I doubt the, air drill water separator based, catch can we have been discussing is totally effective, you can clearly see it does help a lot when you empty it. Seems to work well without one really.

I hope that is helpful.