PCV for low vacuum camshafts?

[amdscooter]

the pan evac check valve in the header collector will supply the vaccum to pull it out

I get that the vaccum is created by the exhaust gasses passing past the front of the check valve orifice on the header collector. My question is where does the flow originate? Ever apply a vaccum to a bell jar for an experiment? Once the air is evacuated from the chamber to the point of the strength of your vaccum source/pump, nothing moves. You cannot pull anything out without flow though the crank case. Where is the flow coming from? Minus a breather on top of one of the valve covers I'd guess past the front or rear main.

Unless there is considerable blowby, there should be very little flow, even at higher depression.  It would be prudent to use a limiter to keep crankcase pressure from getting excessively low and causing oil starvation or seal integrity issues.  Now I'm curious to know how much vacuum can be seen at the port...

I'd think adding a breather to one of the valve covers would eliminate any issues. It would let the vac to flow freely to the collector with a nominal vaccum accumulation. The only reason I asked  was the picture afret posted earlier in this thread:

showed vaccum applied to both valve covers. I like this concept as opposed to a traditional PVC setup where the blowby and suspended oil particles get recycled back through your carb or intake possibly making a bit of a mess in the process.

[e philpott]

no breather vent because the breather hoses go down to a one-way check vavle into the header collector , exhaust gasses passing bye the check valve creates vaccum to pullout crank case pressure , vaccum is good here (not engine vaccum).... there is NOTHING getting recycled through the carb ......

[amdscooter]

no breather vent because the breather hoses go down to a one-way check vavle into the header collector , exhaust gasses passing bye the check valve creates vaccum to pullout crank case pressure , vaccum is good here (not engine vaccum).... there is NOTHING getting recycled through the carb ......

Exactly why I like the setup. I just questioned where the flow on his particular setup comes from with vaccum applied to both valve covers.

[bartlett]

HeY E : you like it setup like that ? I might do that also ...

[jayb]

Adding a breather will just defeat the purpose of the crankcase evacuation system.  I would say that if you added a breather, you'd get far more airflow through the crankcase evac system, and it would probably pull a whole bunch of engine oil with it.  Plus you'd have essentially zero vacuum in the crankcase.  Best thing to do is to seal up the engine if you are going to run any kind of crankcase vacuum.

FWIW I've run both the Moroso system and also a normal vacuum pump.  Both will suck some oil out of the engine, but the vacuum pump is far worse because it creates a higher level of vacuum in the crankcase.  The most I ever saw with my Moroso setup was around 5 inches of vacuum.  I usually run 12-15 inches of vacuum with the pump.  My preference is to use the pump, but run it only at the track, taking the belt off and adding a breather to the crankcase when running on the street.  I've run the Moroso setup permanently on the street, but the engine did use some oil.

[e philpott]

HeY E : you like it setup like that ? I might do that also ...

I like it

[amdscooter]

Adding a breather will just defeat the purpose of the crankcase evacuation system.  I would say that if you added a breather, you'd get far more airflow through the crankcase evac system, and it would probably pull a whole bunch of engine oil with it.  Plus you'd have essentially zero vacuum in the crankcase.  Best thing to do is to seal up the engine if you are going to run any kind of crankcase vacuum.

. . .

Forgive my inexperience.. but isn't good flow through the crankcase exactly what you want to remove the blowby? You don't necessarily need a lot of bars of vaccum to get the suspended particulates moving... good flow volume would do that even at very low vaccum right? Unless more bars of crankcase vaccum is necessary for something I'm unaware of. And if you don't mind me asking, how do you figure such a setup with a valve cover breather might pull more oil out of the engine than a traditional setup that relies on a pump or intake vaccum? Please bear in mind I'm not asking to question anyone's judgement.. I'm asking these questions so that I can get a  better understanding. You know how it is.. little bit of knowledge can be very dangerous.  I'm trying to avoid being that guy.

[Chad D]

Adding a breather will just defeat the purpose of the crankcase evacuation system.  I would say that if you added a breather, you'd get far more airflow through the crankcase evac system, and it would probably pull a whole bunch of engine oil with it.  Plus you'd have essentially zero vacuum in the crankcase.  Best thing to do is to seal up the engine if you are going to run any kind of crankcase vacuum.

. . .

Forgive my inexperience.. but isn't good flow through the crankcase exactly what you want to remove the blowby? You don't necessarily need a lot of bars of vaccum to get the suspended particulates moving... good flow volume would do that even at very low vaccum right? Unless more bars of crankcase vaccum is necessary for something I'm unaware of. And if you don't mind me asking, how do you figure such a setup with a valve cover breather might pull more oil out of the engine than a traditional setup that relies on a pump or intake vaccum? Please bear in mind I'm not asking to question anyone's judgement.. I'm asking these questions so that I can get a  better understanding. You know how it is.. little bit of knowledge can be very dangerous.  I'm trying to avoid being that guy.

Better to reduce the source of the blowby than deal with the blowby.  Increasing crankcase vacuum improves ring seal, to a point, by increasing the pressure differential above and below the rings.  Improved ring seal=less blowby, thus less blowby to remove from the engine.  Also, as crankcase pressure decreases, air mass is lowered, which should reduce pumping losses, though I've never seen this measured independently.

If the flow of blowby gases is slowed, then it should also carry less oil out of the engine, perhaps also slower moving mist particles will fall out of suspension.  If you move more air, more oil mist comes with it, depending on the rate of mist generation inside the engine.

[ScotiaFE]

I'm a proponent of a PCV system. I also live in a shall I say a cold moist environment at sea level and have seen the gooey mess in rocker covers.
If you your not putting a suck on the rocker cover then you will have a gooey mess. Just my experience.

"If I disconnect the hose it pours out of the 3/8" line pretty heavily, out the dipstick and out the opposing breather side as well.  This is a new motor that isn't broken in yet, so maybe it will be better once it has?"
The vapour "pouring" out of the holes would be bothering me more than which PCV gizzmo to use.
It will seat in some, but I would be getting out the air line and leak gauge to see what's up.
Nothing good comes from anything pouring out of an engine.

[amdscooter]

Adding a breather will just defeat the purpose of the crankcase evacuation system.  I would say that if you added a breather, you'd get far more airflow through the crankcase evac system, and it would probably pull a whole bunch of engine oil with it.  Plus you'd have essentially zero vacuum in the crankcase.  Best thing to do is to seal up the engine if you are going to run any kind of crankcase vacuum.

. . .

Forgive my inexperience.. but isn't good flow through the crankcase exactly what you want to remove the blowby? You don't necessarily need a lot of bars of vaccum to get the suspended particulates moving... good flow volume would do that even at very low vaccum right? Unless more bars of crankcase vaccum is necessary for something I'm unaware of. And if you don't mind me asking, how do you figure such a setup with a valve cover breather might pull more oil out of the engine than a traditional setup that relies on a pump or intake vaccum? Please bear in mind I'm not asking to question anyone's judgement.. I'm asking these questions so that I can get a  better understanding. You know how it is.. little bit of knowledge can be very dangerous.  I'm trying to avoid being that guy.

Better to reduce the source of the blowby than deal with the blowby.  Increasing crankcase vacuum improves ring seal, to a point, by increasing the pressure differential above and below the rings.  Improved ring seal=less blowby, thus less blowby to remove from the engine.  Also, as crankcase pressure decreases, air mass is lowered, which should reduce pumping losses, though I've never seen this measured independently.

If the flow of blowby gases is slowed, then it should also carry less oil out of the engine, perhaps also slower moving mist particles will fall out of suspension.  If you move more air, more oil mist comes with it, depending on the rate of mist generation inside the engine.

I absolutely agree it's better to deal with the source of the blowby if you are getting abnormally large amounts like the OP in the other thread.

If you don't mind me treading on your patience a little further..  I'm not quite understanding how an increased vaccum on the back side of the rings help prevent blow by? I would think that you would want the bare minimal amount of vaccum in the case so it's not actually drawing vapor past the rings with an assist from the compression stroke? I'd think you'd want just enough vaccum so there is no positive pressure pushing oil past seals. And if you are drawing the vapor from the valve cover wouldn't' most of the larger particulates of oil not make it that far up into the head? Sorry for the 1000+1 questions. But I've seen a lot of cars with PVC systems that make a pretty decent mess where they dump back into the intake and I'm just trying to get my head around what works best.

-scott

[Chad D]

I absolutely agree it's better to deal with the source of the blowby if you are getting abnormally large amounts like the OP in the other thread.

If you don't mind me treading on your patience a little further..  I'm not quite understanding how an increased vaccum on the back side of the rings help prevent blow by? I would think that you would want the bare minimal amount of vaccum in the case so it's not actually drawing vapor past the rings with an assist from the compression stroke? I'd think you'd want just enough vaccum so there is no positive pressure pushing oil past seals. And if you are drawing the vapor from the valve cover wouldn't' most of the larger particulates of oil not make it that far up into the head? Sorry for the 1000+1 questions. But I've seen a lot of cars with PVC systems that make a pretty decent mess where they dump back into the intake and I'm just trying to get my head around what works best.

-scott

As the piston moves upward on the compression stroke, the clearance volume above and behind the top ring are under increasing pressure, which forces the ring outward to improve the mate with the piston wall (better seal=less blowby).  A higher pressure differential makes for a greater effect (low crankcase pressure from vacuum pump or header evac, high cylinder pressure from compression or power stroke).  Of course, this effect is limited by piston, land, and ring design.  Plenty of builders use thin, flexible, low tension rings to reduce friction and better mate with a dynamic cylinder wall, using pressure differential to couple them instead of static spring tension.  Gas ported pistons are often used with thin rings and a vacuum pump or header evac, they are complementary.

Certainly, ventilating the crankcase of water or other vapors is desirable in a street engine.  With regards to PCV, think about how the vapor/mist is handled... oil mist isn't good in the combustion chamber, but a small amount in a high temperature, low compression street engine generally doesn't cause much trouble, and takes care of a goodly portion of bad guy emissions by burning them.  In any engine (though I'm mostly referring to high compression, high performance engines), the crankcase vapor stream can cause problems with preignition or plug fouling, not to mention fuzzy AF ratios from a misbehaving PCV valve coupled with a big camshaft.  It can be beneficial to remove vapors in an alternate method, like using a vacuum pump or exhaust flow to draw vapors out of the crankcase and exhaust them to the atmosphere or into the exhaust system.  If the crankcase is not sealed, then it may become difficult or impossible to maintain sufficient vacuum to fully utilize the benefits of thin rings and gas ported pistons.

For me, I'm slightly more interested in crankcase ventilation than crankcase depression, but I'm also concerned about moving too much air and sucking oil mist out of the engine (I will use a separator and restrictor) and I don't want the oil mist to pollute my intake (I will use a header evac).  Perhaps this is all mental masturbation, but I already see the mess in my intake in my mild 390, and I want to do something different, mostly to get as much margin as I can running pump fuel.

[amdscooter]

^^^ Thank you very much for the succinct reply Chad. I'd like to avoid the sloppy mess in my mild 390 intake as well. 

[jayb]

I think Chad hit the nail on the head, but I would add one more point.  You don't really need thin rings and gas ported pistons to get the benefits of vacuum in the crankcase.  My person experience with this is with the 511" FE that was in my Mach 1 back in 2005.  It had nearly stock rings (1/16 - 1/16 - 3/16), and they were standard tension.  No gas porting on the pistons.  Adding a vacuum pump at the track picked up a tenth and a half, which is pretty impressive on a mid 10 second car.  So I think the benefits of any crankcase vacuum, even a lower vacuum setup like the Moroso pan-evac system, are well worth pursuing.  I think most of the gains come in the first 5 inches or so of vacuum anyway.