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Turbo's and PCV vacuum catch cans


conkitchen

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Public service announcement:

 

As it might seem obvious, normally aspirated (NA) motors need to vent the crankcase pressure, either to atmosphere (not eco friendly) or to a catch can.

 

Basic atmospheric vented catch cans are good for NA motors since the vapor is pushed out the top of the valve cover. Which in turn collects any oil mist to be reclaimed later. Or more commonly done run back to the air cleaner/carb.

 

On turbos, the pressures inside the crankcase swell under boost and thus need a vacuum assisted PCV catch can. NOTE: I am running a journal type bearing turbo.

 

Was tracing a smoke issue at idle with my turbo for some time. Along with some smoke came an oil drip at the turbo. Turns out crankcase pressures got too high (part of another issue being fixed) and blocked the positive flow of oil through the turbo back into the engine block. I was using a non-vacuum catch can which ended up becoming pressurized.  

 

I have since hooked up a catch can pulling manifold vacuum after the throttle body and instantly solved the smoke and oil dripping.

 

Used two check valves and a tee connection between them. One goes to the brake booster while the other is at the manifold port. Under boost the valves close off.

Edited by conkitchen

But what do I know

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I need to install a catch can on my turbo build as I presently just vent to atmosphere and I cringe about how many polar bears/whales/trees/etc I must have harmed in doing so over the years (/sarcasm, but some truth in that).

Would you mind sharing the routing of your vacuum lines and tee/check valve wrt the catch can please?

Thanks!

Colin

1968 1602

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Oh, PCVs... I don't be having none of them thingies on my '02... can I safely go back to sleep and run my catch can like a NA car with no vacuum going to the can?

I just googled and all the turbo catch can diagrams out there reference PCVs too. Insight definitely appreciated :)

Colin

1968 1602

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Isn't the better way of drawing a vacuum for this to use a venturi and one way valve into the exhaust?

No experience of this but remember reading it in a David Vizard book years ago (so it must be true!).

rtheriaque wrote:

Carbs: They're necessary and barely controlled fuel leaks that sometimes match the air passing through them.

My build blog:http://www.bmw2002faq.com/blog/163-simeons-blog/

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Isn't the better way of drawing a vacuum for this to use a venturi and one way valve into the exhaust?

No experience of this but remember reading it in a David Vizard book years ago (so it must be true!).

 

Perhaps, but then it might smoke with any oil vapor spewing into the exhaust.

 

For me the biggest issue was to recirculate the crankcase gases (or blow-by which in my case is the other problem) into the combustion chamber and to alleviate the lower crankcase pressure so the turbo would drain back into the engine.

 

I had run ( before the catch can) the PCV to atmosphere via a K&N filter attachment and it blasted my engine bay with oil spray.

But what do I know

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I also need to do this on my new turbo engine.  What brand/type catch can did you use? Is it the dual chamber variety?  Also did you use any particular type/brand of pcv valve or just a generic?  In your second picture, what is the silver,cylindrical part just to the left of your finger.  Is that part of the oil catch can setup or something else?

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I also need to do this on my new turbo engine.  What brand/type catch can did you use? Is it the dual chamber variety?  Also did you use any particular type/brand of pcv valve or just a generic?  In your second picture, what is the silver,cylindrical part just to the left of your finger.  Is that part of the oil catch can setup or something else?

The catch can is internally baffled and is shown in the first image (sorry for the quality) next to the radiator. It was acquired from ebay. Liked the bare metal and black look plus the vacuum gauge. That other thing is the altitude compensator. It's part of the idle and metering system for factory turbo's. Suffice to say your car likely does not have or need this. The PCV valve was the BMW style commonly had and used for the brake booster. Ebay has em as does any part supplier.

Edited by conkitchen

But what do I know

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The real issue about crankcase ventilation is making sure the breather is large enough to flow the amount of air that is produced by the leak past the piston rings (this happens to all engines turbo or NA.)  It is a % of the total amount of  air that the engine is pumping so the amount of air over a given amount of time goes up with engine speed as well as throttle position and boost pressure (in the case of turbo charging) 

 

Where you take the air out of the engine is very important,  you want it to be from a place that is not in direct contact with oil and oil vapor.  If the vent is near any moving parts inside the engine there will be oil cast off flying around an if the air is moving quickly past that point you will get a lot of oil along with the air leaving the engine. You want to run as large of a vent and hose as you can,  if you slow the velocity of the air down the oil will be much less likely to follow the air out of the engine.  you also want to have some kind of baffle in the system to help separate the oil and air (look inside the stock valve cover and you will see that they built it with a cover over the vent to try and reduce the amount of oil being splashed right on the outlet)  The problem with the stock valve cover vent is IT IS TOO SMALL if you are running anything more than a reasonably stock engine.  High compression, High engine RPMs and Boost pressure will cause a serious increase in crankcase vent air volume and the stock breather is not big enough!  There is also the problem of tired engines that have excessive blow by (bad ring sealing) 

 

I do not recommend venting the crankcase back into the intake unless you have made sure you are not moving a lot of oil with the air.  It does not take much oil to cause a lot of smoke for one, also a small amount of oil will cause engine detonation very quickly and can cause serious damage if not caught in time. 

 

The problem with trying to pull a vacuum using the intake manifold and a PCV valve is that under wide open throttle (on NA engines) or boost (turbo engines) there is no vacuum being produced to pull the air out of the crankcase (in the case of a turbo engine, if you are not using a 1 way valve you will be pushing pressure back into the crankcase) Under the conditions that the engine is making the most crankcase pressure your system is not doing you any good at all!  Using an exhaust venturi  type vacuum pump it will not do anything at low engine speeds and light throttle settings. 

 

On the NA race engines that have Wet Sump oil systems we use an extended neck on the valve cover filler with a couple of baffles to help separate the oil/air and at least a 1" ID hose to the catch can (make sure you put big enough holes in the catch can to flow the amount of air that will be going THROUGH it! If you look at any pictures of the race cars from the late 60's-70's you can see the modified valve covers.   On the dry sump engines we either run the crankcase breather right back into the dry sump oil tank or seal the engine completely and run a larger scavenge pump and actually pull a vacuum in the engine using the oil pump ( I usually pull 10-14" of vacuum at 7000 rpm)   

1970 1602 (purchased 12/1974)

1974 2002 Turbo

1988 M5

1986 Euro 325iC

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Exhaust discharge point will eventually coke/plug up on an exhaust discharge point. The high load temps of exhaust is around 900-1100F. Oil on the exhaust tube interior will cook and coke up.

The baffle/oil separator in the M10 valve cover is too small to do much separation. Reference a M20 or S14 valve cover baffle. Make a big one like those have or make a decent external oil separator and send the oil back to the sump. I've done the oil return bit. Pass the oil laden vapor thru some ss pot scrubber material to get the oil to separate, then drain the fallout oil to the sump.

This early engine vent design on the M10 never was setup to collect any oil from the vent. Later designs needed more due to the environmental concern.

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

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....This early engine vent design on the M10 never was setup to collect any oil from the vent. Later designs needed more due to the environmental concern.

 Exactly why I went with a vacuum canister for my turbo situation. Non-turbo M10's should be okay without (vacuum) for PCVing. For me and the turbo oil flow, the non-vacuum vent would build up too much internal pressure and push oil past the turbo seal.

 

Although I now concern myself about too much vacuum as it may impede oil flow into the pump and for crankcase splash.

I am pulling .04 MPa which is 5.8 PSI converted to HG = 1.18 or VACUUM. I notice my oil filler cap is under vacuum which may not be good.

 

Two steps forward one step back it seems.

Edited by conkitchen

But what do I know

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A full PCV crankcase system has two connections. One to suck out the vapors and send them to the intake with a flow limiting valve (PCV valve). The second connection would be an filtered air inlet to the crankcase usually from a hoky filter mounted in the air cleaner housing. When vent vapor flow got too much for the flow limiting valve to handle, the excess went out the normal air inlet.

I was where you are now with drawing a negative pressure in the crankcase until I made the second air vent.

The M10 had no air inlet connection because it is not a PCV system, only a vent system and only the vent on the valve cover exists.

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

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Read on the interweb:

 

The max normal idle vacuum readings for an engine should be between 17" and 21" of mercury.

My calculations are (at idle) .04+ MPa converts to 11.8" of mercury. Which jives with my #3 piston low compression test.

 

I think I'm safe even though my oil filler cap is under suction. Perhaps it won't leak oil then.

 

If I introduce a second "air leak" to relieve pressures I'll be chasing my tail trying to get the damn thing to idle below 1k rpm. These turbo fuel pumps have all sorts of intended leaks in them to control idle, boost, and WOT, etc...

Edited by conkitchen

But what do I know

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I've been following this thread with interest as I am just finishing up a turbo engine build.  After trying to digest everything, I am still uncertain as to what the best possible solution is for crankcase ventilation/oil return on our non-pcv turbo engines. Can anyone spell this out for me?

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