Positive Crankcase Ventilation 101 (TECH)

Regarding the confusion on Mr 42’s crankcase ventilation post

Crankcase ventilation is needed to take care of piston ring blow-by. This excess air p***ing through your piston rings from your combustion chamber to your crankcase is full of hydro carbons and bad for the environment and your crankcase, if not taken care of it will cause a pressure rise in your crankcase, blow seals, cause leaks, and the fuel will dilute your oil.

Since it’s bad for the environment someone thought it would be a good idea to put it back in the engine and burn it. The easiest way to do this by a vacuum connection on the intake manifold. The problem here is that just putting a big hole on the intake is that it will act like a big vacuum leak (which it is) and **** up your idle mixture/speed.

The first versions used a fixed orifice to control flow like Mr 42, which is a big compromise, since the blow-by volume is also different depending on vacuum and rotational speed of the engine (rpm). It will really work at only one condition but will not cause the devastating air leak at idle. The opening needs to be variable, enter the PCV valve.

The PCV valve is a pressure operated flow controlling pintle valve.

Manifold vacuum will lift the pintle off its seat (closed) towards an orifice, high vacuum will move the pintle far into the orifice creating a small opening and vice versa.

Strong vacuum signal = idle, deceleration condition = little blow-by = small PCV opening = no upsetting idle mixture.

Intermidate vacuum signal = cruising condition = moderate blow-by = intermediate PCV opening .

Weak vacuum signal = full load condition = large blow-by = large PCV opening.

The PCV valve will also protect the crankcase in case of a manifold backfire where the high pressure will force the pintle against it’s closed position.

During really high blow-by conditions when PCV valve size is not big enough, air is also going through the breather hose into the air cleaner because then you also have a vacuum condition there that can be used.

See, that was not so hard.

 

Tunglegubbin,

That was a damned fine description of the PCV operation. Thanks!

 

<font color="green">He said "pintle"!!!

huh-huh, huh-huh...

Very decent description! </font>

 

[ QUOTE ]
Tunglegubbin,

That was a damned fine description of the PCV operation. Thanks!

[/ QUOTE ]

Yes it is.

My attempts to "steer" Mr 42 to the TECH-O-matic piece was to show that his setup (even though it worked to some degree) did have some drawbacks.

By not having any control of the va***me "signal" (tapping off the underside of the manifold and running the tube directly into the old road draft connection to the crankcase) I believe would upset the carb fuel/air mixture as well as the vac "signal" to the distributor.

Without sounding critical, (I did ask if there was a PCV valve somewhere in the setup) his configuration allows for what would in effect be a big va***me leak.

If you study the TECH piece on "PCV's for Flatheads, the PCV VALVE IS used.

 

Hi Dave and Tunglegubbin

[ QUOTE ]
The first versions used a fixed orifice to control flow like Mr 42, which is a big compromise, since the blow-by volume is also different depending on vacuum and rotational speed of the engine (rpm). It will really work at only one condition but will not cause the devastating air leak at idle. The opening needs to be variable, enter the PCV valve.


[/ QUOTE ]

I agree that my solution is probaly not the best in the world.
But it works as a compromise (and in thousands of Volvo Engine's to).

And the good thing is if someone can tell me wich type of PCV valev i can use, i can connect one in 2 minutes, since i have my plumbing on the upside of the manifold.

The Chevy PCV Valves i have tried did not work, rough idle.


Thanks Tunglegubbin for educating me, i needed it (at least according to Dave )

 

Great description of what PCV is all about.

In addition to keeping the air cleaner, PCV also makes engines live longer. Before it was required by law (early 60s), PCV was an option, mainly used on fleet vehicles, in the 1950s.

 

So does any one care to comment on how the race-car vacuum pump crankcase ventilation system works (benefits, drawbacks, etc...)??

 

[ QUOTE ]
So does any one care to comment on how the race-car vacuum pump crankcase ventilation system works (benefits, drawbacks, etc...)??

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If your refering to Funny car or Dragsters that run on alcohol or nitro methane; fuel collecting in the crankcase (from blowby) CAN cause an explosion.

Most, (well at least the one I help with) use a 100% crankcase ventilation system pump that "injects" the fumes into the exhaust headers where the fumes can be burned up.

 

Well Dave, I have the Evac system that plums into the headers, and it's a MAJOR pain in the ***. It seems like I blow those little checkvalves all the time!

I was wondering about the belt driven vacuum pump setup. I see a TON of bracket racers, and a few of the faster street racers running them, and like I said, I was wondering about the benefits or drawbacks of such a system.

 

Did a search on Google
http://vca2.viperclub.org/forums/showflat.php?Cat=&amp;Board=UBB14&amp;Number=452330&amp;page=0&amp;view=collapsed&amp;sb=5&amp;o=&amp;fpart=all
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Here's a couple of Hot Rod Magazine articles that more than support the idea:

In the first, a 381ci SBC on an engine dyno gained 25-30HP "throughout the curve" with a belt driven vacuum pump pulling just 10in of vacuum in the crankcase.
A second test on that same engine while on the dyno, with the pump's vacuum line disconnected, showed the pump itself draws 6-9HP just to turn it over at high RPM..


The gross or total gain then could have been as much as shocked:..39HP.. at 'almost' 10in of vacuum minus the 6-9hp losses to drive the belt driven vacuum pump.Click to read the HotRod article

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I've used Evac systems for 20 years (the kind that dumps into the exhaust collector) since I read about the performance increase and engine longevity...!

But the one problem I've encountered frequently has been one way Check Valve failure.

Does anybody offer a better check valve for this type of system...?

Mark

 

Possibly off-topic, but Tony Shumacher's (sp?) Top Fueler was sitting at our school the other day for their little recruiting deal. The entire Formula SAE team and I could not figure out what the line was that ran straight from the block into the fuel distribution block thing. Is this some sort of crankcase ventilation thing?

 

Does a pcv valve need to be oriented vertically to work right?

 

[ QUOTE ]
Does a pcv valve need to be oriented vertically to work right?

[/ QUOTE ] <font color="green">I doubt it, they aren't truly vertical on a chevy.

There is a spring in there so it should work either way.

Mr 42, If you have adjusted the carbs without the PCV then you will have to re-adjust with it, you will be changing the air/fuel mix.

Maybe that's why the rough idle?

Just a thought. </font>

 

[ QUOTE ]
Well Dave, I have the Evac system that plums into the headers, and it's a MAJOR pain in the ***. It seems like I blow those little checkvalves all the time!

I was wondering about the belt driven vacuum pump setup. I see a TON of bracket racers, and a few of the faster street racers running them, and like I said, I was wondering about the benefits or drawbacks of such a system.

[/ QUOTE ]

Yeah, the Evac check valves don't last long.

Our vac pump (crank driven) is probably using some HP, (we run a TOP dragster which is putting out about 5000 HP) but when NHRA and IHRA decided that there was too many crankcase (oil pan) explosions; they made one or the other manditory.

From what I have learned from the bracket racers; many "fatten" up on fuel and were starting to have the same problems. (oil pan explosions) So NHRA and IHRA started to "suggest"; (this may have been made manditory since I last talked with some of the bracket racers) that either an Evac or Positive Crankcase Ventilation Vac Pump be used.

Both IHRA and NHRA have decided that the time it was taking to clean up after an oil pan/crankcase explosion (and spreading oil all over the place) that a crankcase ventilation system MUST be used for almost all cl***es.

So any benefits of using these systems is mainly for the track operator, but fuel induced oil pan explosions are not as frequent either. (which means you "save" your engine)
Throwing a rod isn't covered!

It's strange you mention "street racers."
I just happened to watch a street race a while ago. The guy was using NO. (Nitrous) He must have had a lot of blowby (or REALLY worn cylinders) because about 100 feet off the line, there was the BIGGEST explosion and fire I've ever seen in a stock (well it was licenced for street use!) automobile!!

The car burned to the ground!

My friend that sells NOS installations told me after that incident, almost every street racer customer that bought an NO system, also bought a crankcase vent pump!!

 

[ QUOTE ]
Possibly off-topic, but Tony Shumacher's (sp?) Top Fueler was sitting at our school the other day for their little recruiting deal. The entire Formula SAE team and I could not figure out what the line was that ran straight from the block into the fuel distribution block thing. Is this some sort of crankcase ventilation thing?

[/ QUOTE ]

If you had said, "the line runs straight from the block to one of the headers"; then that would be a coolant pressure relief line. Eliminates a "puke can."

We "top up" the coolant (water) after every run. Our cooling system is not under very much pressure, but as the car is being staged, the water is starting to warm up (and expanding) so the excess is "piped" to the headers and turned to steam.

 

nope, went straight from the back of the block (or driver's side head*) to the billet fuel block thing right behind the blower.

*Is there really a driver or p***enger side on a dragster?

 

HRTH, I think the main reason that many street and drag racers use a vacuum pump is that a negative pressure in the crankcase helps ring seal, thus resulting in more power. It is not necessarily done as a replacement for a PCV. The theory being the hp required to run the pump is more then offset by the gains in hp due to improved ring seal.

 

OK all i have on my sbc is the typical breather tube at the front of the engine so exactly how do i get around this?please explain in real simple terms as i am a simpleton and also it must look quite 50's trad also explain what i need to buy and what it has to go to and from..........Marq

 

[ QUOTE ]
HRTH, I think the main reason that many street and drag racers use a vacuum pump is that a negative pressure in the crankcase helps ring seal, thus resulting in more power. It is not necessarily done as a replacement for a PCV. The theory being the hp required to run the pump is more then offset by the gains in hp due to improved ring seal.

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Thanks 38Chevy454;

YOUR reasons are probably more important to racers than "lunching the engine!" because of poor crankcase ventilation.

I got "caught up" explaining how the pumps help avoid fuel fumes ac***ulation in the crankcase.

The negative pressure affect on rings is definatly a plus.

 

alright... I'll have to see what I can afford!

I remember a couple of years ago Mr Gasket had an electric crankcase pump at SEMA... when I called them to see if they ever went into production they said they were drawing too much amperage, so back to the drawing board... maybe they have it fixed now. An electric pump would be pretty simple!(and probably cheaper than the belt drive units! )

Thanks for the info guys!

 

On my 351C I installed a PCV valve and grommet into the valve cover and up to the air cleaner. I know the valve was installed correctly as it fit into the grommet only one way. Problem was, when I would get on it, the dipstick would come out partially and throw oil. Right now I simply have the tubing running from the grommet into the aircleaner, I see very little by-p*** in the tube or under the air cleaner lid but the dipstick will still lift up a bit although only occasionally. What gives? It's the short bus for me.

 

[ QUOTE ]
OK all i have on my sbc is the typical breather tube at the front of the engine so exactly how do i get around this?please explain in real simple terms as i am a simpleton and also it must look quite 50's trad also explain what i need to buy and what it has to go to and from..........Marq

[/ QUOTE ]

Marq, we already have PCV TECH 101.
So let's start PVC Tech 201

ALL internal combustion engines have some blowby. (g***es burned and unburned) that escape past the piston rings and into the crankcase.

These g***es mix with the oil and over time can cause a black "gooey mess." Anyone who has "cracked open a flahead" can testify to this. The second problem in a crankcase is water vapor; byproducts of combustion and cool moist air that causes condensation.

The blowby and the moisture need to find a way out of the engine. Bringing the engine up to FULL operating temperature, (which won't happen with "short" trips to the store) will "boil off" the condensation but it still needs a way out. Ford flatheads tried using a "road draft tube" that was supposed to "draw" the unwanted moisture and blowby from the engine. The tube came out the front of the manifold and snaked down under the engine.

BUT, to "sweep" the fumes out, there has to be an "INLET" for fresh air. Both Ford and GM use the OIL FILLER TUBE as an air intake.

Unfortunatly both companies didn't use a very good FILTER medium in the filler caps, and as a result dust would get drawn into the crankcase and mix with the oil.

Now, if you changed the oil often, this kept the dirty oil problem to a minimum. But the fumes still needed a way out.

Enter PCV (Positive Crankcase Ventilation)
Polution laws made it clear that you could not just "vent" to the outside air; so a system was developed that when a va***me "signal" wasn't needed for advancing (or retarding) the distributor or would upset the fuel/air mixture it could "draw" the fumes (and moisture) into the combustion cycle of the engine by way of the intake manifold.

The full explanation of the valve's operation is at the begining of this thread.

GM started using PCV valves that were mounted on the valve cover and connected to the carb or intake manifold. (the path to the crankcase was by using the oil return paths)

How to incorporate a PVC. (without it being visable on the outside of the engine)

First a va***me "signal" source needs to be found. The va***me is present in the intake manifold, so if a tapped hole on the underside of the intake manifold is made, a PCV valve can screwed in place and a tube or hose positioned to either the road draft connection tube for a flathead or just left hanging under the manifold. (Small Block Chev)

For the type of valve to use; first it wants a pipe thread the on the outlet side. Then a little research of the size of your engine (c.i.) and the size of the carb. (CFM) With these pieces of information in hand, stop by a GOOD auto supply house and they will (well should) be able to come up with a suitable PCV valve.

One side NOTE: If your going to just hang the valve UNDER the intake manifold, expect it to need replacement once and a while.

Finally, the oil filler cap (on either flatheads or SBC's) needs to be UPGRADED.

Use the best you can buy, (I like K&amp;N's) because your now going to be pulling MORE air INTO the engine thru the filler cap. And be sure to clean the filter every time you change oil.

 

[ QUOTE ]
Does a pcv valve need to be oriented vertically to work right?

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I think most PCV valves need to be vertical to work properly. I've only noticed one PCV valve mounted horizontally from the factory. If you can shake it and hear the plunger rattle in the case, I don't think it will work laying down. Vacuum lifts the plunger and gravity closes it. I think it would just lay in the open position after the engine was started. You can hold it up and **** on it. If you have to blow hard to get it to seat then I'd say it was hanging up.

.

.
This is one from a 1990 Isuzu trooper II V6. It was mounted horizontally with hose connections from the factory. It's all plastic with no heavy plunger. It seems to be spring loaded. I cut one of the hose ******s off for my application but it's made with a hose ****** on each end. My uneducated horse sense tells me that different cubic inch motors would need different size PCV's (blowby volumn). I figured the V6 would be close to my 255 CI flathead. (no I didn't check the CI of the trooper it's close enough for me) I'm building a hot rod for the street not an Indy car.

My horse **** er horse sense engineering.

 

Yes, in princip, different size valves for different size motors.
But I cannot see it being that critical as long as you're in the neighborhood, i.e. a valve for a 307 should work for 350.

And the PCV valve is spring loaded so I don't think mounting positions matter, gravity load on the valve pintle is very little compared to what the vacuum/flow will do to it.

 

Oh I'm sure the vacuum will open it. But will it modulate as the vacuum changes if it's laying on the side? I just think it will hang open. To be honest I'm more familliar with the valves from the 60's and 70's. Some of the newer ones may be more sophisticated.
.

.
This is another arrangement with a generic valve but I'm not super confident it will work exactly as designed. It's my prototype.

 

BTTT
any ideas for my previous reply about my 351C? FatHack? Anyone?

 

Jimmy, if I read your post right, you said that you're running the PVC inline between the valve cover and air cleaner. Right?

The PVC valve should be run between the valve cover (on one side) and a vacuum source below the throttle blades...such as a vacuum port at the base of the carb. In most cases the opposite valve cover should have a hose running to the base of the air cleaner ( without a PCV valve.) Basically, one side ****s, the other side breathes.

The vacuum signal it's getting from the air cleaner is probably not nearly strong enough to **** up all the blow-by.

Hope that helps.

 

Hey I hooked up a PCV system on my SBC and I want to make sure I got this right. On one cover I connected a genereic PCV valve to the PCV vacuum fitting on the carb. On the other I have a generic open breather. Is this setup correctly?

Tommy- I don't think it will matter if the PCV is on its side or not. The vacuum should be great enough to actuate the valve regardless of its' position.

Cheers,
Tim

 

[ QUOTE ]
Hey I hooked up a PCV system on my SBC and I want to make sure I got this right. On one cover I connected a genereic PCV valve to the PCV vacuum fitting on the carb. On the other I have a generic open breather. Is this setup correctly?

Tommy- I don't think it will matter if the PCV is on its side or not. The vacuum should be great enough to actuate the valve regardless of its' position.

Cheers,
Tim

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I just went out and grabbed one out of the cabinet. It looks like an old Ford. I can **** the valve open with no problem in the vertical position. Blow through it like a backfire and it shuts off tight. Lay it on it's side, it opens but the plunger just lies there partially open. You have to really blow hard to close the valve. It takes a lot of pressure to overcome the friction of it laying on it's side. Vertically the weight of the plunger makes it fall naturally to the closed position. I may be over ****ytical about it but this one definately won't function the same laying on it's side as it would standing up. Try it if you have a clean one. My mouth is my flow bench but it's never been calibrated. I'm saying that to close properly it needs to be vertical..ish. I know most lean over some. and no wise cracks about borrowing my flow bench.