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#1
January 15th 2003, 18:08
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crank case ventilation
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. 
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#5
January 16th 2003, 17:47
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Me thinks thats not such a good idea....
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.
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Brian 73 Superbeetle
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#6
January 16th 2003, 20:34
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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.
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Julian '74 Super "If you are under control you're going too slow" - Parnelli Jones
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#7
January 17th 2003, 06:27
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My (usually incorrect) 2 cents
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 
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If its worth having I can't afford it.
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#8
January 17th 2003, 08:30
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Re: My (usually incorrect) 2 cents
Quote:
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Brian 73 Superbeetle
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#9
January 17th 2003, 13:50
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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
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#10
January 21st 2003, 05:44
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....
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.  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!
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#11
January 21st 2003, 20:00
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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).
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P.J.Berg. Last edited by BergRace; January 21st 2003 at 20:05.
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#12
January 21st 2003, 20:20
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QUESTION?
How would you vent the case with a dry sump system? THANKS!!
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Julian '74 Super "If you are under control you're going too slow" - Parnelli Jones
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#13
January 22nd 2003, 14:24
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Quote:
Brian
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#15
January 22nd 2003, 21:52
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Quote:
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P.J.Berg.
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