legacycentral bbs

OK, so we still have no consensus on where a catch can should be placed to keep the blowby oil from coating our turbos, intakes, intercoolers, and eventually burning in the combustion chamber -- effectively reducing octane and burned oil deposits eventually increasing compression.

What about this product, from that mr fix it site -- any comments on this thing?

http://www.misterfixit.com/envalve.htm

and... would new rings fix the problem -- thereby eliminating blowby at the source?

free5ty1e i just put new piston rings and pistons with every brand new part and i still get a little blow bye, i say it comes from vavle covers and that f pice going to pcv and in the turbo two spots.

i just let the turbo eat the oil they made it that way so no use trying to get it to stop.

yeah, forgot rings have gaps that don't completely close up when the piston is installed.

So... does ANYBODY have a catch can successfully installed (and doing its job, keeping oil out of the turbo wheels/intake/intercooler/combustion chamber)??

...and maintaining a properly functioning PCV system both on and off boost?

i would think the answer is no.

ok i think my dad is crazy he wants me to unplug the vacum lines from the vavle covers and put a little filter on that so its open air IS HE CRAZY. he really thinks thats how it should go we get in to fights cuz this oil in the turbo bullshit.

Yeah you know I wouldnt mind if we came up with a solution that was "not-so-friendly" to the environment... frankly I'm more concerned with all the oil in my turbo and BOV and intercooler and combustion chamber. I mean, sure I can just take it all apart every week and clean it all out, and use some top-end cleaner in the engine, but it would build right up again.

Damn tree-hugging hippies and their regulations

i have followed many of these topics and have tried many different setups with my my00rst. i was about to swap my setup again and configure it the way the manuals show but when i look closer at it it seems to be flawed. it shows the valve covers and the crank case drawing air from the intake pipe, have you ever held your hand over this pipe? it creates vacuum and with the addition of boost it creates alot of vacuum. wouldnt this cause air to be pulled out of the valve covers and the crank case instead of vice versa? am i looking at this wrong?


jay

That's what you want......the crankcase to be under vacuum. It helps the piston's seal, and oil seals from leaking.

ya but on the diagrams that were posted on the first page of this thread it shows them also getting fresh air from the air intake to mix with the blowby gasses before it goes into the pcv. also it only shows fresh air to the valve covers, no vacuum at all. i understand the concept of how it all works im just not following the diagram for this reason.

so... do we need two catchcans, one for each line running to the intake? Sealed catchcans or vented?

The diagram only shows the arrows for part throttle. If you read the text portion of my scan
http://www.main.experiencetherave.com:8 ... system.jpg

It mentions there are two specific conditions, part throttle where air is drawn in through the rockers, and sucked into the manifold through the PCV valve.

Under full throttle, blow by gasses are sucked in through the PCV valve & the rocker vents in the intake.

For turbo's.....it should be the same/similar under part throttle.

Under full throttle since you have positive manifold pressure, all the blow by gasses would be sucked out through the rocker vents into the intake.

Okay, after much consideration and investigation, here's my newly refined theory on how and why the PCV system works. Let me know what you guys think.

I have a feeling the key lies in the fact that the fittings are not all the same size, and the fact that one of the plastic fittings has a specially shaped end.

Refer to the diagram of the turbo PCV system to get your bearings: http://www.graphics.cornell.edu/~v/vacuum/

Let's quickly address the long tee that connects the two valve covers to the middle of the block -- it's just there to help make sure vapors freely move between the heads and block, since the closed-deck block interface may otherwise impede that.

Now, the breather fitting towards the rear of the block has a 19mm outer diameter. It connects via a short hose to that "F"-shaped pipe. That F-shaped pipe is 19mm OD at the bottom, but tapers down. The lower arm of the "F" has a 15mm OD, and connects to the PCV valve on the intake manifold. The upper arm has a 12mm OD, and connects to a little plastic connector that goes into the compressor inlet boot.

The PCV valve actually functions both as a metering valve and a check valve. The plunger inside has seats on both ends. For the purposes of this discussion, the details of the metering functionality aren't critical. The check valve functionality is, though. The valve only allows gases to flow into the intake manifold, and not out of it, irrespective of the pressure differential that may exist.

The little plastic 12mm connector has a special shape. Its end is cut on the diagonal. It basically has an opening facing downwards, at the compressor inlet. This helps the compressor pull a vacuum on the pipe.

Then there's the other side of the setup -- basically two hoses from the valve covers which join with an equal-length setup, entering the compressor inlet boot from the side.

Okay.

So, now, there are basically two types of situations, categorized by manifold pressure. The first is vacuum -- idle and low load -- and the second is boost -- high load.

Vacuum: In this situation there is a strong vacuum sucking through the PCV valve. Thus, the intake manifold sucks crankcase fumes out the block, through the "F"-shaped pipe, through the 15mm hose, and into the PCV valve. How do they know not to go through the 12mm hose? Well, three reasons. 1) The 15mm hose is depressurized, 2) The 15mm hose is larger and so easier to flow into, and 3) The 15mm hose is closer. And how do they know not to go out the valve cover breathers? The pressure at those breathers is close to atmospheric, while the pressure at the crankcase breather is lower than atmospheric.

Boost: In this situation, the PCV valve is closed because manifold pressure is high. However, the 12mm plastic fitting kind of takes over the same role. The compressor is spinning, so there is a partial vacuum at the compressor inlet. The shape of the 12mm fitting kind of collects this vacuum, so to speak. So crankcase fumes come up the "F"-shaped pipe and go through the 12mm fitting into the compressor inlet boot. Again, they don't come out through the valve cover breathers because the pressure there is higher because they don't have that tapered angled plastic fitting concentrating the vacuum at the compressor inlet.

So in both situations, fresh air comes in through the valve cover breathers and yucky crankcase gas exits through the block and enters either the intake manifold or the compressor inlet.

There's also this middle ground when manifold pressure is very close to atmospheric pressure. I'd guess that in this situation a mix of the two above things happen, probably more of the "boost" situation, since the compressor is spinning (otherwise you couldn't have atmospheric pressure at part throttle).

So what does this mean for those of us who want to modify the system but maintain its functionality? Here are my guesses:

- If you're installing a turbo with a horizontalish compressor outlet (i.e. any EJ turbocharger aside from our stock one), and need to somehow relocate the "F"-shaped pipe, I think the way to do it is to get some extra 3/4" hose and use it between the pipe and the block. If necessary, you could also use some 1/2" and 5/8" hose to extend the arms of the "F", but too much and I think you might risk upsetting the balance.

- If you want to install a catch can to just prevent oil from collecting in the intercooler, I'm not sure there's a good way to do it while maintaining the PCV system's functinoality. It would have to go between the "F" pipe and the 12mm fitting, but a) there's very little room there and b) a restriction in there seems like it might very well prevent PCV from working at all when on boost.

- If you want to eliminate the PCV system entirely, I think what you'd do first is put two 1/2" breather filters on the two valve cover breathers. You'd then remove the F-pipe entirely. You'd cap off the two fittings on the compressor inlet boot, and cap off the PCV valve. Now here's the tricky part. You still need to pull at least a light vacuum on the block breather. So you'd need to run some hose from the 19mm breather on the block out to some low-pressure portion of your engine bay. If you just find a place where lots of air passes by as you drive, and end the hose perpendicular to that airflow, the venturi effect might be enough. You'd probably want to stick another filter at the end of this hose. I don't know what the right size of hose to use would be. It seems like if you used 3/4" hose you probably wouldn't get the gas velocity you need, so you might start with a 3/4"-to-something-smaller adapter and then use narrower hose to go out to this low pressure area. This way your car will pollute more, and drip oil wherever it goes (just like back in the 50s!), but the air intake charge will be cleaner.

- If you're modifying your intake, you can relocate the fitting that goes to the valve covers to wherever you like, as long is it's not exposed to too much vacuum right before the compressor. The other fitting does need to stay more or less where it is, though, since it needs to allow the compressor to suck from it.

Your thoughts?

I had a catch can on the top hose of the F pipe and it was collecting a bright orange colored liquid and smelled like gas. I could accumulate quite a bit of liquid in a 10 mile trip. I ended up just removing it until one of the ESX techs gets a chance to hook up my flat intake manifold and top feed injectors i'll be purchasing from him in December. He said he would install the catch can at the same time.

What if some kind of filter was put between the 12 mm pipe and the comppressor? Wouldn't that prevent oil from coating an intercooler as that's the only upstream source? I understand that it would need to be low restriction to not affect functionality, but something could probably be found.

Now for broken F-pipes ... Could one just build an F-pipe replica out of correct diameter piping (be it copper, plastic, whatever) or is the taper so critical that the system would no longer work efficiently? I would rather fabricate one than source one of these brittle, rare, and likely expensive units.

I realize that maybe only the Subaru engineers would know the answer to these questions entirely (or maybe not), but we can speculate in their absence.

Steve

Bright orange liquid? Weird. What in blowby is orange?

few things of note and a few questions to go along with it.

when doing my turbo install (which isnt done yet thanks to this) i broke the f piece. i didnt read this trhead till tonight but pmd matt about the sizes of the hose extensions. so i wne out and spent 2 bucks on 3/8 5/8 and 1/2 hose 2 of which will be the right size 1 will probaly not. the one will be the one which attaches to the center of the crankcase at the bottom of the f picece which appears to be 19mm od. my f piece didnt want to budge and so i broke it off which left the piece of hose that attaches the f to the crankcase on the crank case. it had hardened over time and it took a standard scewdriver and a hammer to get it off.(cracking it into pieces) in order to remedy the absense of the f i will be using a hose attached to the crank case to a "t" that is 19x3/8x5/8 or some other variation that makes all of the pieces connect to where they need to go.

the question is will this upset the balence enough to cause damage to the motor in any way? or is it a non problem? or in worse case senario, a trial and error hope for the best type deal

Let's just decide to stick with English units here, since that's what you're gonna find at a hardware store. 19mm is about 3/4", 15mm is about 5/8", and 12mm is about 1/2".

So you're proposing replacing the F-shaped piece with a 3/4"-to-5/8"-to-1/2" tee. You'd run a long 3/4" hose from the crankcase up to the tee, and a short 5/8" hose from the tee to the PCV valve and a short 1/2" hose from the tee to the plastic 12mm fitting.

If I'm right about my guesses, I think that you're on the right track... You do want to make it easier for the gases from the crankcase to get to the 5/8" fitting than to get to the 1/2" fitting. So if the tee has the 3/4" end across from the 5/8" end, that might work. Maybe you'd even stick a small restriction in the 1/2" hose.

You're gonna have to try and see... I don't know how you'd be able to test that it's working right, though. Anyone have any suggestions?

thats exactly what im thinking of its just that i need to get 3/4 hose and a new tee. i may use a tee with a 3/4x5/8x5/8 because that will be easier to find and use a 5/8-1/2 adaptor to make it fit properly.

im still a little wary on the sizes of the hose and will get back to you on it tomorow.

on a last note the piece that sticks out of the crankcase that conects to the f piece was also lined with that orange stuff mentioned earlier.

when i installed my turbo, i cut the F pipe below the fork and then used a longer hose to move the F and then clamped it.

I dunno what that orange fluid was so i pulled the catchcan off.

Do you remember what size hose you used to extend it, dzx?

I seriously doubt that the tubing size is going to matter as far as which way gasses will flow. If the other end of the tubes were at exactly the same pressure, the gasses would prefer to flow down the tube with greatest diameter (or more exactly, the tube with the lowest total drag taking into account length and number and shape of bends). The drag can be expressed as a pressure drop. The fluid will flow down the tube with the greatest pressure differential, after accounting for the pressure drop due to drag.

In practice for gasses, the drag is so low as to be negligible, so the gas will flow based upon pressure differential alone. IE will not flow down the smaller tube unless there is less pressure at the other end compared to the big tube.

I DO think the shape of the tube near the compressor is crucial, it appears to be a venturi device, otherwise it would flow big-time in the wrong direction.

I've seen some strategies for disassebling PCV systems and adding filters, catch-cans, etc. They are messy and if neglected can clog and blow seals, and possibly splash oil places you don't want it in surprising quantities, such as on hot manifolds.

But wouldn't the diameter of the hoses matter in situations where the pressure differential would otherwise be small, like when you're near atmospheric manifold pressure?

And it seems to me that if the hose going to the compressor inlet were too large you wouldn't get enough of the venturi effect.

Do you think the length of the hoses matters much? Does a longer narrow hose present more of a pressure drop at any given flow rate than a shorter narrow hose?

Yes you would not get a proper venturi effect if the intersecting hose is too big. The equations to figure this out are very complex, but for air the intersecting hole needs to be pretty small and shaped correctly. For water there is more leeway since it is more difficult for the fast-flowing water to make a U-turn and back up the vacuum hose. Interestingly, the higher the pressure and velocity of the flowing media, the greater vacuum can be generated. Perhaps some of the problem is that at higher boost, you are sucking too hard on the PCV system ??? In any case you are flowing at conditions not calculated by the Subaru enginers, so the venturi may not work as designed one way or the other.

These type of venturi effect devices are pretty common, like the fittings that go on the faucet in labs to provide a vacuum source, and the vacuum-generators that can be fitted on air compressors. The important thing is that the fluid in the big pipe needs to be flowing rapidly and in a laminar fashion for it to work properly. Too much turbulence and no worky.

Longer hoses will present a greater pressure drop, but unless very narrow, things like elbows and surface roughness in the tube will have greater effect. One elbow typically presents as much pressure drop as twenty to fifty FEET of pipe, and that's a smooth elbow at that. Elevation change is important for heavy fluids like water but means zippo for air.

I think it is likely that the hoses are different sizes to eliminate the possibility of a flow reversal, or unpredictable flow. If both hoses go to the same place, or where the pressure is the same, then the size is crucial. Let me give an example:

If I am trying to distribute water to two places predictably, I want to make sure the main pipe (header) is way bigger than the two others' combined cross-sections. So, I use a 3" pipe. I want the flow to go to point A and B, unless a valve is closed. I pipe with 2" pipe to point A, and 1" pipe to point B. Now I'm sure there is adequate flow in the header for water to pour out both A and B when the valves are open. If the header were too small, say 2", then when both valves are open, virtually all the water would come to point A, and point B would get nothing.

Also, if the header AND both A and B were piped the same size, the SLIGHTEST difference in length, roughness, number of turns, temperature, etc would cause virtually all the water to come out the pipe with least resistance. Note this is true only if both pipes are open at the ends (same outlet pressure exactly), or go to the same place or same pressure.

I would say the hoses are different sizes due to the last point, to make flow predictable and not subject to reversing or stopping due to some slight fluctuation.

If you didn't mind making swiss cheese out of your pipes, fitting a pressure monitor to several of these hoses would tell the truth. Usually a 1/8" hole and tubing is all that is needed, and a sensitive manometer. Then with this set-up you can also find out the truth about intake pressures and pressure drops.

Huh. From what I could tell from reading other Subaru forums, it's generally accepted that running high boost causes the intake charge to become oil-heavy because crankcase pressure gets high, but maybe at least some of it is that the PCV hose's pressure is too low. That's a very interesting thought. It seems reasonable that the venturi would be designed according to the expected airflow.

I'm curious to know what the corresponding part looks like on other Subaru turbo motors designed to flow different amounts of air.

I think I understand what you're saying, professor, and it seems convincing to me. So we think we have a pretty fair understanding of how the system works.

So you think Jason would be just fine with the tee as he's proposed?

Of course there is always this system...

http://community-2.webtv.net/PAGEBUILDE ... VACUATION/

A bit extreme and I'm sure emmissions testers would have a heart attack, but no doubt effective.

Shows just how much vacuum you can get with the venturi. Note they just used a crude 45-degree connection and got a lot of vac, maybe the geometry isn't as important as I thought.