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Previous Next Up Topic Engines / Subbug - Subaru Power / Catch-can drain? (15290 hits)
By @Jeff GS Date 2010-01-05 02:23 Edited 2010-01-05 21:56
I've had another of those - "while I'm doing this" inspirations, and hoping to get some insight if this will, or won't work.

Tied into my 2.0L's PCV system is a remote catch can, plumbed so that all airflow going into the PCV system flows through the can, and any blow-by during on-boost driving is also routed through the can.

My crankcase vent system closely follows the OEM routing, as shown here:

It has been modified slightly - adding another T intersection and creating only one path from the air filter intake tube to the PCV system plumbing with catch can in-line (edited pic to clarify):

The intent is to trap any oil vapors before they make their way into the intake of the turbo during boost situations.  Here's how the catch can looks (can object on the right):

The lower side fitting goes to the PCV system, engine side, while the top fitting goes to the intake tube.
You can see the drain fitting on the bottom, installed to remove any accumulated oil build-up.

Note the general location of the can - situated directly above the turbo oil drain line - and this is what got me thinking...... (and I'm finally getting to the point!)

Could I run a simple drain line off the bottom of the can Tee'd into the turbo oil drain back into the engine?  This would make it an auto-drain, truly no maintenance and fully closed system!  Certainly the plumbing isn't any problem.  My main concern is any possibility of vacuum or pressure being on that drain line (from the attached PCV system) upsetting normal turbo oil drain or actually drawing oil up into the can?  I don't "think" that would be any issue, given the normally short time the engine is on boost, and otherwise free-flowing air route through the can.

I wouldn't mind a 2nd opinion though!

By @Jeff GS Date 2010-01-05 22:18
I edited my "modified" picture to more accurately depict my layout.  As I see it the PCV system has 3 modes of operation:
1) At idle with high manifold vacuum - PCV valve is closed and small amount of crankcase pressure is vented through main vent and valve covers back to intake and atmospheric pressure in the intake tube.
2) At cruise/no boost - PCV valve is open, drawing air in from the intake tube, through the valve covers, crankcase and out through the main vent and into the intake manifold - purging out residual water vapor and other contaminants.  Note the restrictor which was copied from the OEM system, it seems to bias the vapor flow towards the PCV valve from the main crankcase vent.
3) Under boost - PCV valve closed again, excess crankcase pressure is vented out through valve covers and main crankcase vent - back through the PCV plumbing - through catch can and into intake tube, and then drawn into the turbo with the small amount of vacuum it is creating in the intake.  This is where I want to trap the "blow-by" and excessive oil vapors in the catch-can.

I'll probably end up trying it without the drain to start (one less thing to have to deal with at initial start-up), then add it later to see if it makes any difference in turbo operation or excess oil accumulation in the can.

I guess some are thinking by now I really over-obsess some of these details!  :-)

By Jay H (X-20) (ManxVair CC) Date 2010-01-07 04:34
Hey Jeff,
This catch can.... Is it simply a catch can with inlet and outlet? Does it have filter media in it? Is it a moisture separator complete with inlet dip tube forcing a directional change for the air?

By @Jeff GS Date 2010-01-07 12:55
Hey Jay,

Here's more detail on the can:

That baffle section sits snugly in the bottom, with the lower "disc" just above the can side inlet.  The lower disc has a fairly large center hole allowing gasses to pass up/down through the baffles.  You can see the upper disc has outer holes positioned to prevent line of sight gas passage through the baffle assembly.  Above the baffle assembly is a round piece of fuel cell foam that fills up the upper 1/2 of the can.

Any gas passing through (from the side inlet) has to travel down to the lower inner tube side openings, back up through the inner tube past the lower disc, then jog out to the openings in the upper disc, then up through the foam to get out the top.  Normal non-boost operation would have the gas flow traveling in the opposite direction.

I'm hoping the "labyrinth" passages will encourage trapping oil vapors in the bottom of the can.  I studied several catch can designs, ranging from simple open containers with foam inside, to more elaborate factory style with internal baffles, etc. to formulate a design for mine.

By Jay H (X-20) (ManxVair CC) Date 2010-01-08 00:51
Jeff, I would think that your design would be a good idea. I wonder how flow reversal will affect the ability of the catch can to condense the vapor effectively.

The PCV will close under boost, but you'll be drawing the entire PVC system upstream of the valve into a vacuum as it all ties upstream of the compressor wheel.

Do you have a screen on the top port (inlet in your drawing) to keep fuel cell foam from reversing and making its way into the piping should it begin to break down or something of that nature?

Under normal circumstances I would see this as an asset, but should you break a ring land and begin to experience blow by, this can may function more as a supply of oil in the much more destructive liquid state to be supplied to the compressor wheel as opposed to simply having oil vapor make its way to the compressor wheel.

I realize this would not be the normal operating condition of the engine, but trying to play Devil's advocate.... thinking along the lines of mechanical preservation/casualty control as well. I'd hate to see your oil vapor condenser shell out an expensive turbo should you experience blow-by.

You've discussed having an open drain to the oil pan. If a drain were in place, I would think there is less concern that the catch would have as much potential to supply liquid to the turbo inlet pipe.

I think a simple drain would need to have a liquid trap as well. I've seen AC drains that didn't drain because of air being sucked up through the drain line. It simply would not allow the water to drain out, and as a result, the water level would overflow and drip all over. I'm applying what I know about fluid dynamics with plumbing in this situation. A simple fluid trap stopped the air flow through the drain allowing the liquid to drain.

Your catch with a drain that incorporates a trap (in such a way that the trap isn't emptied when you mash the loud pedal) should be the ticket.

I like your design. You've obviously done a lot of thinking about what you want and its construction! :-) I do enjoy all the pictures along with your entire build.

By @Jeff GS Date 2010-01-09 17:22
Hi Jay,

Still pondering your reply.  To be honest I hadn't really considered any real liquid "volume" accumulation in the tank, other than maybe a couple tablespoons?  You do raise some good points though.
I think that if a lot of oil did accumulate, eventually it would build up high enough to run back out the side port from the PCV system - which is the typical airflow direction probably 70-80% of the time (off boost).  If that happened, I'd think you'd really start to see some serious smoking problems out the exhaust with that oil being drawn into the intake system!  I do have that AN hose arced up pretty high though (to help drain any accumulation of blow-by oil back into the crankcase before it ever reaches the catch can....)  I suppose there is some marginal possibility this "liquid height" could rise up high enough to cause problems - but that would be a pretty extreme situation.

Generally, I don't think oil would accumulate enough to make it up and out the top vent in the can (in any significant volume) to cause any problems inside the intake tube and into the turbo?

As far as the auto-drain feature - thinking this through a bit further, it seems like the turbo drain point in the head/case simply becomes another crankcase vent, especially since it should be above the general oil level in the crankcase (as would any turbo drain).  It apparently doesn't cause any drain problems from the turbo, I suppose because of the slight pressure from the turbo likely overcomes the crankcase pressure 95% of the time.  I think T'ing into this drain with a source of some relative vacuum probably wouldn't be such a  good idea.  One option would be to install a valve in the catch can drain line, either a 1-way valve, or maybe a normally open solenoid valve that shuts when the engine is running - allowing drain back whenever the engine is off.  I like fewer electrical devices though - preferring the KISS approach.

Simple ideas....are never quite that simple are they?

By @Jeff GS Date 2010-01-09 17:35
Oh yea, one other bit of info:
I pulled out a new PCV valve and tested it for flow from the "three modes of operation" idea above.
I found, using lung power at least, I could not get it to shut when drawing vacuum on the intake manifold side.  It closes down some against the spring - but I couldn't get it to close completely.
Blowing into it from the manifold easily make it seal up 100%, so that part is correct.

It seems the PCV system is drawing vacuum into the intake then - both during idle and cruise situations, and shuts under boost.

For the FWIW dept......

By Jay H (X-20) (ManxVair CC) Date 2010-01-10 01:17
Jeff, you are chartering untested waters. Knowing your abilities and skill, I think you've probably hit at all the angles. I'm interested to see how this functions for you. I imagine when you fire this thing up, there will be dancing in the streets. Keep up the great work.

FYI: I was worried about my PCV valve in that the spring pressure might not be strong enough to keep the barrel close to the seat under hard acceleration. This was due to my flipped manifold and rear engine configuration. (My PCV valve faced forward while angled slightly down) As it turns out, even with hard launches, I haven't noticed an inability to seat under boost. I'm not sure which direction your PCV will face, but if it is forward, I would think your PCV's spring would hold the barrel close enough that with the increased pressure under boost, she should shut just fine.

By ron w 1919 Date 2010-01-16 03:03
it seems to me if you have that much blow bye maybe you should tear the engine down and fix it.the rings are obviously junk!!!Also if the catch can shuts all air flow down then be prepared to put all the seals back in that the pressure in the crank case blows out!just a thought!
By Jay H (X-20) (ManxVair CC) Date 2010-01-16 11:12
Ron, I was simply suggesting that should you experience blow by, it may be more expensive to repair if that situation took place. I didn't mean to suggest that he is currently experiencing blow by, or that he ever would.

Sorry to have confused the situation. You are right though, If you are experiencing blow by that badly you should do a tear down.

By ron w 1919 Date 2010-01-16 12:39
I used to run an blown 572ci bbc in a dragster,we vented the crank case to the exhaust.we put a tube with a 45 degree cut in the exhaust flow causing a vacuum ! I must say that I must have miss read you post.Sorry for that!! do you have a post of you build?  Ron
By ron w 1919 Date 2010-01-16 13:18
so tell me how did the radiator project come out?I am building an inntercooled twin turbo 2.0 and using a dual pass radiator and a polaris 4wheeler radiator on the heater hoses .am an running separate fans and controls.the dual pass is behind the engine,the polaris is above the trans .both are have ducts from underneath . I haven't been able to test this as it,s been -10 here.more ducting may need to happen?the polaris rad has its own fan switch built in the rad that makes things a little easier .I am running a porsche 5 speed final gear ratio of 3.63 .I can easily pull less gear with the 300hp-315 lbs of torque.may have to build wheelie bars,LOL.this is a street drive rail ! can't wait to blow the doors off of just about anything! I love things that a very fast,things get boring more power may be needed!!! 
By @Jeff GS Date 2010-01-16 15:17
Hey guys - I didn't mean to imply I'm trying to control bad blow-by problem, after all the OEM PCV system just vents any blow-by back into the intake.  My goal is to build a car that could survive something like a hill-climb or even the Nevada Silver State Challenge open road run.  While either of these isn't likely to happen, knowing (or at least thinking) the car is capable of such performance is the goal.
I've read on NASIOC about Subaru's having a bit of "extra" blow-by when run under heavy or extended boost conditions, so just trying to anticipate.  It's my take a turbocharged street vehicle probably sees actual hard boost about 10% of the time, the rest it's running along N/A, and the stock crankcase vent system works just fine.
But what happens when the guy drops the flag, you Hammer it and hold the throttle down for a few miles!  I think in that situation some extra blow-by control could come in handy!

So back to reality....  :-)  Ron, if you're referring to my radiator install, I'm not there yet.  It's also been damn cold here with little work getting done on the buggy.  I've identified a couple of off the shelf radiator candidates from AFCO and Griffin, but either isn't quite exactly what I need - either a little too big or outlets in the wrong spots.  In fact, I'm going to have to finish up the front suspension work first just to see where radiator lines can be run going past it.  That work will be happening this Spring and Summer.  It was a huge hurdle last year just getting the turbo/intake/intercooler/exhaust system work completed!

Overall I'm excited, I'm seeing this Summer as when I'll finally be doing some finish assembly work on the chassis and hopefully get it running for the first time!

By Charles W 2165 Date 2010-05-06 19:17 Edited 2010-05-06 20:01
I know you are trying to think the pcv thing through throughly. The only thing I can contribute is that a catch can should be in the path back to the high vaccun port of the pcv and also the line back to the turbo inlet should be as long as possible. My son has the mann provent and our own plumbing setup using another pcv turned around backward (the line from the valve cover to the turbo inlet) blocking the port in front of the turbo inlet unless it's under boost. He is running a 30r turbo and a 3 inch inlet but it's really close to the pass valve cover. Thats where the oil in our setup was coming from. The catch can will get moisture in it and unless it's heated the moisture will stay there so it really needs it's own sump that can be drained. Also the good oil needs to go back to the pan. Most subys loose oil when they are run hard and I think thats the reason a lot of them spin rod bearings. The kids driving them are used to running the s**t out of a na honda and the oil staying in the motor. They don't check the oil often and it dissappears. In the case of the hot rodded ones the oil gets hotter and gets fuel diluted and gets thinner making for even more oil loss. The only problem with the mann provent is the orings are for a diesel motor and they swell up and need to be replaced with ones for a gas motor. It's amazing the amount of lines required on a high tech turbo motor.
By @Jeff GS Date 2010-05-07 19:27 Edited 2010-05-07 19:29
Hi Charles,

If I'm reading your description right - that would put the catch can in the line directly above the "2" in the OEM picture above.  I don't see how that would work all that well, considering the PCV valve closes under boost?  When on-boost, excess bypass gasses would route back into the intake (pre turbo) unimpeded, while off-boost it would "catch" any blow-by going to the PCV valve, which I'd think would tend to be minimal during those periods?

In my layout, the catch can gets air passing through it during all phases of operation, both on (vapors) and off (intake air) boost, though it doesn't do anything to catch any blow-by during off-boost (normal PCV) operation.  That's the theory anyway.....  :-)

Previous Next Up Topic Engines / Subbug - Subaru Power / Catch-can drain? (15290 hits)

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