PDA

View Full Version : crank case ventilation


Tony Z
January 15th 2003, 18:08
Guys, my mind has been wandering again and I thought of something, but want to know your opinions on it.

The general idea with crank case breathing is to have a central box that recieves the extra pressure / oil from the rocker cover, as well as vents the case from the stock vent and / or from the fuel pump location. This box possibly vents to atmosphere or to the carbs.

what about this?

Use the box as above, but instead of venting the valve covers to the box, run them direct to the sump - easier if you have a deep sump. that way, any extra oil in the covers will drain direct to the sump. also, if you go thru a long sweeping bend, you wont have a problem with the oil collecting in the cover, it will drain direct to the sump. you could then also run a "scavenging" system to the breather box that sucks a bit of a vacuum in the cranksace and not worry about sucking oil from the valve covers and spilling it all over the tarmac. The easiest way of having this type of vacuum is to create a venturi effect in the exhaust pipe.

blah blah blah, you get the idea, I am just starting to ramble now.

bren
January 16th 2003, 08:36
valve cover vents to sump idea is certainly food for thought...

hmmm.... (scratches chin)

kdanie
January 16th 2003, 15:51
Makes sense to me..... Where did I put that drill? Seriously, I will look at my engine this afternoon and see if I can pull this off without a complete teardown.
ken

Sandeep
January 16th 2003, 16:47
Maybe I'm missing something but don't the pushrod tubes serve this function already ? (Let oil back to sump) :confused:

Sandeep

zydeco
January 16th 2003, 17:47
and here's why. If you drill a hole in the sump, put a hose fitting on it, and plug the hose in to it, you've got a hose dangling around waiting to catch something as you're driving. If it snags something and yanks the hose out, you've got a big hole in your sump and no oil in a matter of seconds. Also, if you have enough blow-by, the breather may pump so much air into the sump, you'll make whipped cream!

The snagged hose bit is still a potential problem if the CCV fitting is at the top of the valve-cover but at least you'll have a *much* slower loss of oil than if you put it a hole in the sump.

Then again, maybe you're talking about routing it to the upper portion of the sump but I still think its a bit too risky.

lightning bug
January 16th 2003, 20:34
I'm not sure if it can be done. But if it can, keep in mind it has to drain above the oil level in the sump. Otherwise you risk the oil just backing up to your valve cover. Probably not worth the trouble IMO.

richiep
January 17th 2003, 06:27
Can't remember who told me this now, but I was told that the reason why cars have their breather connected to the induction system is to suck air out of the crank case to stop the oil churning and frothing, not simply to collect the waste oil.

It may have been a mate of mine who works for Jaguar doing power train, so I'll try and mail him later to ask him - haven't seen him for a bit tho'.

Who ever it was they were horrified when they saw the breather box on my Speedster and talked me into putting a pipe fitting on my air cleaner and running the breather to that.

Since being told this I have noticed that every production car I have seen has the crank breather connected to the induction system in some way - must be a reason for it.

Bye



:)

zydeco
January 17th 2003, 08:30
Originally posted by richiep
Since being told this I have noticed that every production car I have seen has the crank breather connected to the induction system in some way - must be a reason for it.


I think this is usually done for emissions purposes on newer cars (since the mid 70's in the US) to prevent hydrocarbons from the crankcase from venting to the atmosphere. Still a good idea though. The only drawback is the added potential for getting the carbs fouled.

kdanie
January 17th 2003, 13:50
The hose from the crankcase vent to the carb intake was started in '67 here in the states for emission purposes. Before that engines just had a breather to the atmosphere. The hose to the air cleaner does not have enough vacume to evacuate the pan. Racers use a venturi tube in the exhaust or a belt driven vacume pump to put the case/sump under a negative pressure.

The pushrod tubes are the only means of returning oil to the sump from the heads. At sustained high rpm they may not keep up or the centrifugal (sp) forces during a long sweeping corner prevent the correct drainage.

I agree that a hose is a bad idea but a -10 hard pipe, formed to the contour of the case, from the bottom of the rocker box to the sump above the oil level would help the high rpm issues but could possibly make the sweeping corner problem worse by giving the oil another way to get to the head. No way to be sure without tesing it.

The best solution is a multi-stage dry sump oil system with stages sucking oil from the rocker boxes.

ken

Oliver Knuf
January 21st 2003, 05:44
To clear it up a bit....

If you correctly want to ventilate your engine (I speak about engines over the standard Volume and enough horsepower), you have to plug your valve covers, your standard oil breather tower connection and maybe your fuel pump cover, if possible. These 4 hoses will be plugged to a box with at least six openings.

http://www.csp-shop.de/shop/images/techtips/13816.jpg

As you can see, the four hoses are there to vent the engine, the oil spray and dust is kept inside the box, there's a small drilled metal piece inside to seperate the oil and the pressed out air. The air is sucked through the top openings of the box through hoses into the carbs, where it is again burned. This system makes sense, because if you build higher volume/hp engines, that naturally produces more energy through more power, you have to route the bigger amount of compressed air out of the crankcase. The original opening isn't enough!

In the history of the beetle engine, err, to be correct, of EVERY engine, you'll see, that a crankcase ventilation is used everytime (we speak about normally aspirated 4-stroke engines ;) ). The gases inside the case, that are compressed and pushed/pulled through the case, have to go somewhere. If there wouldn't be an opening, where it can leave, the gases would leave the case through the easiest opening, on a beetle engine that would be the crank pulley oil drain opening, or the sealing ring at the flywheel. Emission control makes it, that these gases have to be burned, because they are pretty toxic! Before this law, engines could blow-by everywhere to the atmosphere (remember the rubber opening at the end of the old oil fillers on the beetle, long pipe). You could even use small K&N air cleaners on the top openings of the box, to route the air to the atmosphere, but after a while, the oil gases will drip out of it and it'll look ugly!

What you wanted to have is a faster oil-return from the heads. When you plug hoses or pipes from the heads to the sump, you'll have a more constant oil-pressure in curves and under high revs. Every VW boxer with a high volume pump has the problem, that the oil is running back into the sump much too slow, after it was pressed through the pushrods into the heads. Believe me, if you run an engine under full load, high rpms, shut it off, run to a valve cover, plug it off and you've got a half Liter of oil on the road, when you're fast enough! (I tested that with a plug in the valve cover) That's a common problum and occurs only under high rpm/load, so don't mind of, just vent your engine correctly, that's it!

BergRace
January 21st 2003, 20:00
That setup is not perfect though, it (the box) should extend further down with a little sump shaped in the middle with an oil return line for the de-vaporized oil.
This would leave four breather hoses available above oil level, and two vacuum lines(to the induction system).
It should also contain an upwards labyrinth between the four(at the same level) breather hoses and the two vacuum hoses(on top).

lightning bug
January 21st 2003, 20:20
How would you vent the case with a dry sump system? THANKS!!

verbeekb
January 22nd 2003, 14:24
Originally posted by kdanie
Racers use a venturi tube in the exhaust or a belt driven vacume pump to put the case/sump under a negative pressure.

How about, one, maybe two of such tubes into a Remmele exhaust, similar to the manifold heat system evacuation pipe in a Bug muffler. The connection to this could be on the front side of the muffler and would be really close to the stock breather opening, a short length of high temp teflon/braided .. which ever you can find in a suitable (big) diameter .. Would there be enough suction on one or two of these pipes??

Brian

BergRace
January 22nd 2003, 21:49
Originally posted by lightning bug
How would you vent the case with a dry sump system? THANKS!!
The exact same way.

BergRace
January 22nd 2003, 21:52
Originally posted by verbeekb
How about, one, maybe two of such tubes into a Remmele exhaust, similar to the manifold heat system evacuation pipe in a Bug muffler. The connection to this could be on the front side of the muffler and would be really close to the stock breather opening, a short length of high temp teflon/braided .. which ever you can find in a suitable (big) diameter .. Would there be enough suction on one or two of these pipes??

Brian
You need a header with the vacuum pipe in the middle of the collector, along with a one high-flow one-way valve at the conection hose.

lightning bug
January 22nd 2003, 23:11
Thanks P.J.

Richie
January 23rd 2003, 03:56
I'll add my 0.2 cents (euro, that is) here to this already lenghty thread.
Running a pipe or hose from the heads to the sump will fill the head on the outside with oil when making a long sweeping turn. This already happens without the hose, through the pushrodtubes! To cover this problem you can lengthen the pushrodtubes on one side, where they'll enter the block. This way you'll create a barrier so the oil can't flow as easily into the pushrodtubes as with standard tubes. Don't block the openings between the lifters and the pushrodtubes completely, duh!
You can use hoses or tubes but then you'll have to fit one-way valves in them, and it would have to be rather large diameter hoses or tubes. At least #10.

I prefer venting the crankcase-fumes into the exhaust as these fumes tend to lower the octane rating when you feed them to the intake (just a little, but it does). This way you could get a problem when running very high compression or boost.
Hope to have added some usefull info.

Cheers

Richard

verbeekb
January 23rd 2003, 14:04
Dank je wel Richard!

The fact that the octane rating would be influenced by the oil fumes never occurred to me.

Brian

Richie
January 24th 2003, 07:45
You're welcome, graag gedaan!

I believe the Dutchies are coming! As far as I know there are three of us now on this forum!
Nice to know that you're working for a very interesting firm! ;)

Cheers,

Richard

verbeekb
January 24th 2003, 13:03
Yeah .. :) .. it -is- a very interesting place Richie, and I can't get enough of it .. They gave me the title "Classic Specialist" *grin* .. and it gives me tons of time to chat with fellow Porsche and VW nuts about all sorts of things, right at work! I also like the looks on the face of a 914 or 356 owner when they discover I don't really care whether they own that car or, for instance, a new Cayenne, or maybe both. And I get to play with Porsche parts every day and get paid for it too! :) .. Come over some day, maybe with Wally, for some coffee and a little tour, I'd love that.

Brian

Michael Ghia
February 4th 2003, 04:45
In an oil crankcase breather system, there must be an outlet somewhere into the atmosphere... whether that's straight back into the carb so the gas gets burned or not. If you don't have the outlet (i.e. you use a complete sealed system) it will blow an oil seal as the pressure built up inside above 4,000 rpm is pretty great.
One way which you can help the system is to use a vacuum pump on the crankcase breathing system. If you actually pump air out of the engine crankcase, you'll find you pick up hp. It has been seen to free up 10hp on big V8's.
Racers use this all the time to great effect.
Mike Ghia

Oliver Knuf
February 5th 2003, 04:48
Porsche engines run close breather systems, as they suck the air again in and burn it. I used to have a similar system earlier on my central air filter unit in my 1st 2l Type 4, but after that, I use the filter mounts left and right. It's pretty identical if you route it into the filter tops or into the atmosphere. The filter tops are a bit better, as you still have a small sucking effect on the breatherbox!

lightning bug
February 5th 2003, 20:26
Originally posted by Richie

Running a pipe or hose from the heads to the sump will fill the head on the outside with oil when making a long sweeping turn. This already happens without the hose, through the pushrodtubes! To cover this problem you can lengthen the pushrodtubes on one side, where they'll enter the block. This way you'll create a barrier so the oil can't flow as easily into the pushrodtubes as with standard tubes. Don't block the openings between the lifters and the pushrodtubes completely, duh!
You can use hoses or tubes but then you'll have to fit one-way valves in them, and it would have to be rather large diameter hoses or tubes. At least #10.



Cheers

Richard

You can just use windage pushrod tubes for that.

verbeekb
February 6th 2003, 07:46
How about running a dry-sump pump to assist the breather system? .. And how about lubrication of that side of the pump .. ??

Just some food for thought ..


Brian

Bugzilla
February 21st 2003, 00:01
Originally posted by BergRace
You need a header with the vacuum pipe in the middle of the collector, along with a one high-flow one-way valve at the conection hose.

Yup. It's called an eductor, and I run one on my baja: http://rap.midco.net/bugzilla/new_wheels/wheels022.htm
http://rap.midco.net/bugcollector/DSCF033.jpg
http://rap.midco.net/bugcollector/apr03001.jpg

It is very simple to build one... just weld a piece of pipe to the exhaust, near the collector. Get a one-way valve (I think it is a GM part) and thread it on the pipe. Then run a hose from the valve to the breather tower, or any place on the case you want to vent. I tapped the valve covers and connected them to an aftermarket breather with an oiled foam element. This provides a place for clean fresh air to enter the crankcase. The eductor pulls quite a bit of vacuum, and you don't contaminate your intake charge... it all goes out the exhaust. The one-way valve keeps any pressure pulses (like a backfire!) from traveling to the crankcase.

If you want more details on how I built mine, let me know.

Troy

Chris Percival
February 21st 2003, 06:05
Very neat! Do you believe that is the optimal angle of the pipe? How is the pipe finished inside? Its is square, or it cut parallel with the exhaust pipe?

Bugzilla
February 21st 2003, 09:14
Originally posted by Chris Percival
Very neat! Do you believe that is the optimal angle of the pipe? How is the pipe finished inside? Its is square, or it cut parallel with the exhaust pipe?

The pipe was just an off the shelf piece from a plumbing store, matched to the threads on the valve. The research I did said 90 degrees to the exhaust flow is optimal, but I put mine at 45 degrees for a clean install. I had the whole thing welded up and sent out for ceramic coating. The guy who welded it for me said he did the weld first, and then ran a drill bit down the pipe to open it up to the exhaust flow (rather than drilling the hole first, then trying to weld to it.

Here is an interesting thread describing the concept: http://www.eurospares.com/sucker.htm

And some pics of another install: http://community-2.webtv.net/PAGEBUILDERPICS/CRANKCASEEVACUATION/

You can even buy a kit, if ya want: http://www.csaponline.com/sale/moroso/moroso.htm

Troy

Chris Percival
February 21st 2003, 09:51
And the valve doesn't get too hot? What are these valves most commonly used for? (so that I can go into a parts store and ask for one)

kdanie
February 21st 2003, 12:28
The kits I have seen in the speed shop catalogs are designed for an angled installation like shown in the pictures.
ken

Bugzilla
February 21st 2003, 20:25
Originally posted by Chris Percival
And the valve doesn't get too hot? What are these valves most commonly used for? (so that I can go into a parts store and ask for one)

The valve is a check valve used for the GM A.I.R system (I think). It is a "Standard Motor Products" part # AV7. Pick an application from the following page that uses the AV7, write down the GM part number, and take it to your favorite parts store. http://www.smpcorp.com/catalog/web_catalog_header.asp?maker=CHEVROLET&batcm=AIR%20CHECK%20VALVE
It should cost less than $15.

I've used mine for about 6 years on the baja. That's a 1600 DP with a tri-mill exhaust, BTW. And it was already starting to rust before I sent it out for ceramic coating (yeah, I sandblasted it first)... the rust you see is under the coating. Next time I will use a NEW exaust system.

Troy