Proper oil catch can setup for a road racer

[99gst_racer]

Great tech article, BTW.
I have a question about it too.


When comparing these setups:

&

I would have assumed that the set-up that has the larger amount of vacuum pulling on the crankcase pressure would be the better performing set-up. While doing some searching, I found that most people aren't able to get more than 2-3 inches of vacuum from the pre-turbo intake pipe (of course, that heavily depends on the diameter of the pipe and which turbo is being used).

I really need to measure my crankcase pressure. I assume I have quite a bit even though my engine's tolerances are fresh and tight. Must be something to do with 40+ PSI of boost. The last time I drove the car, I didn't have the hood on it, and I had a misted my windshield with oil from either the cap or the dipstick.

Also, on the "bigger improved" set-up - is the stock PCV valve still needed with an inline check valve? I assume you have it in the diagram as a back up check valve, right?

 

[Calan]

Paul,

IMHO... if you run a PCV valve, you also run a check valve, since they always seem to leak boost.

The main purpose of the valve is to meter airflow between the IM and CC during low-load conditions (vacuum). As vacuum increases and decreases in the IM, the valve proportionally flows more or less air out of the crankcase. Whether or not that makes a lot of difference on modified DSMs...I dunno. My guess is that most people with heavily modded DSM's probably wouldn't see a bit of difference if the PCV valve was a straight tube (other than a small change to fuel trims). It's actually on my to-do list to find out.

The difference between those two setups ^^^ is that the one on the left preserves the PCV and ventilation aspect of the sytem, while the one on the right would be an all out race setup where you need maximum pressure relief while under boost and aren't worried about the oil becoming contaminated during normal driving.

I know of one person who says they are pulling a consistent 7 in/hg under all conditions. Because of who they are, I believe them. But I'm also not convinced that it's necessarily a good thing to pull that much vac...and they are running multiple mondo lines and have no provision for keeping the oil clean under normal (vac) driving.

It seems to me that about 1-2 in/hg of vac in the CC would be ideal; you would want just enough to provide constant flow out of the CC, but not a lot more. I would think that excessive vac in the CC could cause pumping losses (however slight) just like positive pressure does. That is just a hunch though.

EDIT: Now that I think about it, that very well could be the main reason the stock PCV valve is set up the way it is. By closing off under low-load conditions, it limits the amount of vacuum that can be pulled on the crankcase, which theoretically would make the engine more "neutral" in regards to crankcase pressure... if that makes sense. And of course it also helps keep the AFR more in line at the lower amounts of airflow. Or to be more precise...it makes the ECU's job of keeping closed loop AFR's in line easier.

It would be really interesting to see what happens to fuel trims when a good stock PCV is replaced with a straight fitting. I've got to get the car back together and get on that to-do list.

Tks BTW

 

[kiggly]

Well good luck, but I can't comprehend doing it.

Take a pint of oil, a pint of gasoline, a half can of brake cleaner, and a cup of water and mix them all together really well.

Now... pull the pint of oil back out for me.

Sure, just apply heat. At about 150F or hotter all the light ends of the gas and brake cleaner are well gone and the water is evaporating quickly. Thsi is one reason OEM's try to get oil up above 150F or so as quickly as possible - to reduce oil contamination during short drives.

The 'trash' that comes out of the breather is not particularly dirty or harmful unless the engine is producing something dirty or harmful. I don't see anything wrong at all with putting the oil back into the engine. In my eyes it is much more likely that if somebody is lazy with maintenance they will hurt their engine quicker by running it 1qt low than the slight oil dilution will reduce the oil film strength to some critical level.

The main function of the PCV system is emissions. It is a carnal sin to allow unburned hydrocarbons freely into the air from an emissions point of view. Look at some old cars from before emissions standards. The VERY old stuff just puked out oil onto the roads at the middle of the lane.

Also, I believe around 1psi vacuum in the crankcase is the highest level the main and cam bearing seals will sustain. Higher than this and it will trash the seals because air will get pulled by. If you pull air past those seals, they lose all their lubrication and will wear out quickly. This is a major consideration in OEM PCV system design.

Kevin

 

[my4ATEurV8]

Sure, just apply heat. At about 150F or hotter all the light ends of the gas and brake cleaner are well gone and the water is evaporating quickly. Thsi is one reason OEM's try to get oil up above 150F or so as quickly as possible - to reduce oil contamination during short drives.

The 'trash' that comes out of the breather is not particularly dirty or harmful unless the engine is producing something dirty or harmful. I don't see anything wrong at all with putting the oil back into the engine. In my eyes it is much more likely that if somebody is lazy with maintenance they will hurt their engine quicker by running it 1qt low than the slight oil dilution will reduce the oil film strength to some critical level.

.

Kevin

+2
thats pretty much what i was thinking.

 

[eclipsh]

So Kiggly, what would you say is the best ventilation system to run while still avoiding excess pressure and vacuum in the V/C and crank case? Everyone seems to agree the stock one is not sufficent after cranking up the boost.

 

[doesitonall4rs]

Does anybody know how much boost a stock PCV valve (Check valve) will hold before it starts to leak?

 

[Calan]

Does anybody know how much boost a stock PCV valve (Check valve) will hold before it starts to leak?

It's all over the place. I've tested a new one out of the box that leaked at 17 psi or so, and then I've seen some hold over 20 psi. Just run the $1.49 check valve and it's not an issue.

The 'trash' that comes out of the breather is not particularly dirty or harmful unless the engine is producing something dirty or harmful. I don't see anything wrong at all with putting the oil back into the engine.

I'll agree to respectfully disagree on this.

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For those interested, here is a pic of the first set of large volume filtered cans that we've produced for Brian and Eric. The can on the left is the dual-inlet VC > turbo inlet can, and the one on the right is the single-inlet PCV valve > IM can.

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Let's keep this thread clean and on-topic... please PM me for details or questions on these particular cans instead of posting here.

 

[azules demon]

sorry for dredging up an old post, i have been wondering about ventilation setup for running speed density. since im no long using MAF. i have been looking for a few days now on here and google checking other forums, and i may have over looked it. if someone could point me in the right direction so i can get this project completed id be grateful