Catch Can

[100_Percent_Juice]

Im thinking about fabbing up a catch can which leaves me with 2 questions.

1. Can 1 catchcan do the job of 2? ie hook both lines into one instead of having 2 seperate.

2. What kind of pressure +/- am i looking at for those lines?

[tysonK]

sperry will answer all your questions.

hold on.

[sperry]

One catch can is possible, if you size everything properly with the lines. However, after about 6 different attempts, I can't get either one or two cans to work. Of course my situation is a little different, as I'm dealing w/ a ton of blow-by pressure, an unusual oil-breather configuration, and massive lateral-Gs on the race track.

However, in general, the "best" setup is to run two cans. One in between the valve cover breathers (after the T) and the intake on 3/8" hose, and one in between the crank case breather (after the PCV) and the intake on 1/2" hose. Unfortunately, none of the kits really provide you with everything you need to do it right, you'll have to do some work putting together a real solution, but if you're planning to build your own, you can do it right.

The question is, why do you think you need a catch can? Are you seeing oil in your intake? Does the car see high lateral-Gs? Are you drag racing, or otherwise winding the motor out to high loads/rpms on a regular basis? For the most part, a catch can on a street driven car is really just bling... or at most, for piece of mind. It's not really necessary, and they can be quite a bit of work to get right. I know on my car it's been a *huge* hassle to get them setup properly... but like I said, I'm fighting a bit of a different issue than a mostly stock car would have (my blow by pressure pumps oil out the valve cover breathers under hard cornering).

[100_Percent_Juice]

Thanks, that answers a lot of my questions. I was mainly thinking about doing it after i posted pics of my turbo and there was blow by oil in there and my intercooler. It was just a suggesting by several people. Also I see a little smoke out of my exhaust at random times and that is also a reason people told me I needed a catch can. I really wasn't looking forward to it because I just know something like that can be a pain in the butt. Thanks for your input.

[cody]

I haven't gotten around to installing my Avo Catch Can and as I've read up on it, I'm getting worried that it might not be safe to install it since it's only one can.

I emailed AVO for install directions and they only had the Japanese version available (attached).

This is the clearest instructions I've found. Do they look safe?

The AVO kit came with a T, a hose clamp, zip ties, some little hoses, some random nuts and washers and a length of "garden Hose" sized hose. Of course I bought it from Ezdeno "used" but it seems unused.

If it's a risk at all, I'll abandon the idea of using it since it's really not necessary. The only reasons I bought it is because I understand oil in the intake lowers the effective octane of the mixture and some say an IC coated with oil on the inside is less efficient.

[sperry]

Considering oil in the intake is potentially fatal for a motor (I'm proof) I'd say a catch can is very important on high HP turbo cars.

However, a poor catch can may be worse. I've always been told two catch cans is the *only* way to be sure it's right, but there are also considerations with hose size and plumbing configuration that make the difference between blowing up a motor and cleaning the oil out of the intake. Since I never actually figured it out on my car, and ended up just going to a massive breather can, I'm not willing to comment on what's "right".

Chances are all the "kits" out there are just doing catch cans lip service because 90% of the people out there don't need 'em. And for the 10% that do, they're not messing around with "kits". I tried the Perrin kit... and it didn't work for me. I tried like 40 different configurations to try to get it to work (including adding a second can)... but by the time things were "all set" I think my ring lands were so far gone that *no* catch can could handle the blowby pressure my crankcase was seeing.

So, I'd say, get the opinion of a professional on this one, I don't know anyone in the club that can answer this one in a manner that would be "right". But if you have an hour or six, I'd be happy to sketch out the oil breather system on the WRX, the STi, and hybrid WRX/STi motors, and list all the possible known methods for catching the blowby oil in them. Bring beer and a whiteboard.

[Double Phister]

Originally Posted by sperry

...if you have an hour or six, I'd be happy to sketch out the oil breather system on the WRX, the STi, and hybrid WRX/STi motors, and list all the possible known methods for catching the blowby oil in them. Bring beer and a whiteboard.

How about MSPAINT in a tech thread instead? I'll buy you a beer or three next time I'm up there or you're down here.
I just saw a thread on nazioc with someone showing off their crawford (:shutters: ) breather non-catch can install. Thoughts on that setup?

[8URSTI]

What is the purpose of a catch can?.....To eliminate any oil being put BACK into your engine HOPEFULLY by trappin it in the catch can......To do this you need a vaccum source to suck the oil out of the engine through the catch can and back into the intake. Most people use the intake as a vaccum soarce because it is the easiest way and its they way they do it from the factory. No matter what catch can you have you will always be contaminating your intake air if you route it this way.

Also if you run anything through your PCV valve you are just dumping bad crap into your motor. The 2.0 guys have it easier as they dont have the extra CCV that the 2.5 guys do. Therfore that is why most people claim that 2 catch cans is best to handle the other CCV. So what is another source of vaccum on our motors other than the intake pre turbo and intake manifold(pcv) ????? The EXHAUST!

I have my open valve cover vents looped to eachother and my baffled ones "T"d with my 1 CCV run to a catch can and the catch can is then bunged in downstream after the stock 02 sensor in the exhaust. My lines are also overly LARGE (-10an). To me. This seems like the absoulute best way to run a catch can. You have no way of contaminating the motor and your are getting the required vaccum from the exhaust to take the excess oil out of your motor..........

[sperry]

Originally Posted by 8URSTI

Also if you run anything through your PCV valve you are just dumping bad crap into your motor. The 2.0 guys have it easier as they dont have the extra CCV that the 2.5 guys do. Therfore that is why most people claim that 2 catch cans is best to handle the other CCV. So what is another source of vaccum on our motors other than the intake pre turbo and intake manifold(pcv) ????? The EXHAUST!

Except using the exhaust as a vacuum source is illegal in most (all?) SCCA classes, IIRC. Fine for the dragstrip, but not workable for the majority of people on here that need to comply with SCCA regs.

And the 2.0L motor's oil breather system sucks... it's prone to pumping oil out the valve breathers under high lateral Gs. My hybrid motor (STi block WRX heads) could fill up two Perrin catch cans in 2 laps at RFR. 'Course some of that may have been due to the excessive blow-by from my pistons, but without the secondary breathers there's no way to keep crank pressure from forcing oil out the heads.

Here are some drawings (as best as I can remember w/o a car or service manuals in front of me) that diagram how the whole thing works.

First the layout of the WRX and STi systems:



The only important difference is that the STi has dual breathers on the heads and block, but since they don't plumb into the intake at any point, they don't matter at all in terms of how to hook up catch cans.

Here's the normal operation of the breather lines:



You can see that while the car's under vacuum, the PCV is open and clearing the crank-case of the nasty fumes in there by sucking them into the intake to be burned in the cylinders. To replenish the CC with clean air, the valve breathers suck from the intake.

But when the car is under boost, things reverse a little bit. The CC is still being ventilated by the crank-case breather, but now the draw is from the intake's high-velocity flow, because the PCV is closed due to boost pressure. Additionally, if there's blow-by past the piston rings, the CC is being pressurized by that exhaust gas. So the primary flow should be out of the CCV and into the intake. If that flow can't ventilate enough pressure, then the valve breathers reverse their flow, also bleeding off CC pressure through the oil galleries. What's bad about this, is that on cars with big turbos that are seeing lots of lateral G's, oil can crawl up the side of the valve covers and get blown out the breathers. My WRX had a huge problem with this, partially because of the single breathers in my WRX heads, plus the high CC pressure due to the big turbo on the STi block I was running.

Here are the popular layouts for single and dual catch cans:



The first is the normal way to T a single can into the system. What's crucially important when doing this is to ensure the hose size for the different breathers. You really need to make sure that the CCV lines are significantly larger than the valve breather lines because of the situation where the valve breathers are drawing air from the intake through the catch can. I don't know all the "whys" to how this is supposed to work... but it's what's generally accepted as "okay". Frankly, I wouldn't run a single can like this.

The second picture is the "normal" way to hook up dual cans. This I'm fine with. Basically everything should work just like stock, except if there's ever any oil in the system it's caught before it ends up in the intake.

The third picture is an "ideal" way to put the CCV can in before the PCV so even under idle you're not sucking directly from the crank-case into the intake manifold w/o catching the oil, but doing this requires quite a bit of extra plumbing because of the way the outlet on the CCV is designed... it's really not worth all the extra effort, but it's "ideal".

Now then, while dual catch cans seem to be the right solution, some of us (i.e. road racers) are still blowing an awful lot of oil around the breather lines due to lateral Gs. In this situation, I don't think a catch can is the right solution. The right solution is to avoid any chance of getting oil into the intake by never routing the breathers back to the intake at all.



The first diagram is a basic breather can. The two sets of breathers are simply ventilated to atmosphere with a can to catch the oil/water in the gases. This means the CCV and valve breathers can suck/blow/whatever as they need without the threat of octane lowering oil in the intake.

The second diagram goes one step further by returning any caught oil back to the block, so if you're pumping oil out the valve breathers around long hard turns, it goes back into the block instead of just sitting around in a catch can.

The drawbacks to the breather cans is twofold... 1) They're messy and stinky... you have blow-by exhaust directly blowing into the engine bay. Not so nice on a street car. 2) They're not street legal... there's a reason we have CCV's and PCV's... it's to meet emissions regulations. And finally, on the drain-back can, you end up polluting your oil with water (exhaust condensation) and all the rest of the crap that's in blow-by gases, meaning you have to change the oil more frequently. None of these things are a big deal on a race car, but IMO make breather cans on street cars "too much".

Anyway, that's what I can remember off hand about all this junk... I've tried pretty much everyone of those configurations above and about 20 other ones that didn't work. I'm still not all that confident that I know what I'm talking about on this, since I never got it all working on my car. My current motor is getting built with a drain-back breather can designed by GST Mike, so we'll see how that works... should be good, especially since I'm getting my blown ring-lands repaired as well, meaning a lot less CC pressure to deal with.

[Double Phister]

thanks for the tech scott.

Here's the thread I mentioned

The guy says that condensation isn't an issue because the stuff doesn't sit in the can. What are your thoughts?

[sperry]

Originally Posted by R4ND0M_AX3

thanks for the tech scott.

Here's the thread I mentioned

The guy says that condensation isn't an issue because the stuff doesn't sit in the can. What are your thoughts?

A true air-oil separator will make sure not to have any significant pressure drops so that the water vapor in the gases doesn't condense. If the Crawford piece is a true air oil separator, then condensation won't be an issue, and all the water vapor in the gases will go through the intake and out the exhaust pipe.

However, I get the feeling that the Crawford "air-oil separator" is really just a swirly catch can with a drain. Blowing how water vapor from a small tube into an open can will allow the gases pressure to drop and therefore condense the water vapor into water, which drains back into the motor with the oil.

There's a reason true air-oil separators for aircraft with 400hp+ motors cost twice as much as the Crawford piece. They're a lot more complicated than just a can w/ a drain. However if someone would like to buy one of those things, and cut it open to prove to me it's not just a baffled can, I'd be willing to change my mind.

Also, I wouldn't remove the PCV setup on a street driven car... It's there for a reason, to actively draw crank-case gases out of the block when you're not under boost. This is normally the primary means for keeping the crank-case clean. Under boost there's less vacuum to draw the block clean, you end up relying on blow-by pressure which is made up of the gases you're trying to remove! Without the PCV you'll never really ventilate the crank-case with clean air which leads to sludge buildup and nasty oil. Again, no big deal on a race car since the oil gets changed frequently, but on a street car, no thanks.

[Dean]

I am reviving this thread due to a possible need for one...

Either my 90k engine is getting old and burning it and/or my tune is getting better so I am making more power at higher boost and/or driving it harder now that I have it well setup causing breather dumpage and the net is I am losing oil.

1/2Qt or so per hour of track time at Laguna Seca. I don't drive it enough on the street to know what that consumption level is.

I may have to rebuild/replace the motor at some point, but will probably do this anyway.

This appears to be a simple 1 can solution, but can't figure out which of Scott's diagram it fits probably because I don't know which hose is which.

Not sure I want to spend $300-500 or whatever it is on the GST solution complete with rag breather cap like Scott.

Any updated thoughts/opinions/links?

[Kevin M]

1/2 qt per hour sounds cheaper than a catch can setup. The real question is where that oil is going- if it's passing through the compressor, you need to do something about it. Otherwise, who cares?

[sperry]

Dean, I don't trust any single can solutions that don't address both the crank and valve breathers. And any single can solution that does address both circuits is going to be expensive, 'cause it'll have to be big enough to allow the pressure differentials between the two circuits to equalize without pumping crank pressure into the heads.

You might want to look into the Crawford can. I don't think it will handle as much flow as the GST can does, but it's essentially the same device, plus it recirculates back to the intake instead of just vomiting air through a rag. But it's expensive like the GST can is.

Or you can go with a dual catch can setup, and even for relatively cheap if you go the Dean route and fabricate your own out of some 3" PCV pipe sections and caps. Hell, I've got a bin in my garage full of like 5 different catch can attempts if you want to sort through it for parts! We could probably do a dual setup on the car for the cost of some pizza at my place if you don't care how pretty it looks.

[Dean]

Originally Posted by Kevin M

1/2 qt per hour sounds cheaper than a catch can setup. The real question is where that oil is going- if it's passing through the compressor, you need to do something about it. Otherwise, who cares?

I know there is at least some coming into the intake as there was a little buildup on the IC-TB hose & TB last I had the IC off. Didn't actually look into the IC though.

There are <$50 single catch cans out there, so I'm not sure cost is a huge issue.

[Dean]

Originally Posted by sperry

Hell, I've got a bin in my garage full of like 5 different catch can attempts if you want to sort through it for parts! We could probably do a dual setup on the car for the cost of some pizza at my place if you don't care how pretty it looks.

That would rock. Pretty is not my my middle name, Cheap is.

[cody]

I still have the AVO can I bought from the other Dean. It's designed to be a one can solution as there are 3 barbs at the top of it, but reading this thread (as well as trying to discern the crappy Japanese instructions they faxed me) confused me enough to insence my flight or fight response mechanism.

Fortunately, now that I've replaced the 5-30 Royal Purple with 10-30 Royal Purple, I don't seem to have any noticable consumption.

[MikeK]

Originally Posted by Dean

This appears to be a simple 1 can solution, but can't figure out which of Scott's diagram it fits probably because I don't know which hose is which.

The actual square can in those pictures looks identical to mine (mine is a greddy).

[dayofpain]

you actually hurt my brain looking at this.

i have one i need to install. i used to think i knew where it went. now i cant make up my mind where to put it.

[Dean]

Revival part 2...

OK, I have been doing more research on this and have a basic question... Why would anyone want to hook either an A/O separator or catch can back into the intake especially on a race car? It is post combustion, so what is the compelling reason to add any volume post MAF sensor?

I would think you would be far better having it vent filtered to atmosphere. Something like this:

[100_Percent_Juice]

nevermind

[sperry]

Originally Posted by Dean

Revival part 2...

OK, I have been doing more research on this and have a basic question... Why would anyone want to hook either an A/O separator or catch can back into the intake especially on a race car? It is post combustion, so what is the compelling reason to add any volume post MAF sensor?

I would think you would be far better having it vent filtered to atmosphere. Something like this:

Vent to atmosphere is messy, stinky, and not legal for emissions (the latter being the biggest reason most people don't use them, as they're dead obvious at inspection, but that isn't really a big deal in NV since most places are lax on inspections). On a racecar, emissions and the mess really don't matter much, and it's always nicer to not blow exhaust back into the intake since it lowers the effective octane of the intake charge.

But for a street car, it's much cleaner not to have something mucking up the interior of the engine bay, plus you get the vacuum of the intake to assist the catch can, rather than relying on crank case/valve cover pressure just to blow everything out.

IMO, on a street car, I'd run a pair of closed-loop catch cans; on a race car, I'd run an open vented air/oil separator that drains back to the crank.

[Dean]

Originally Posted by sperry

IMO, on a street car, I'd run a pair of closed-loop catch cans; on a race car, I'd run an open vented air/oil separator that drains back to the crank.

OK, that is what I was thinking, but did not see that as the conclusion on IWSTI and such.

Another question I have is why is there a perceived pressure differential between crankcase and heads that has to be dealt with? They are definitely connected by large enough oil drain passages to allow any instantaneous surge to quickly equalize. Is there something I am missing?

[sperry]

Originally Posted by Dean

OK, that is what I was thinking, but did not see that as the conclusion on IWSTI and such.

Another question I have is why is there a perceived pressure differential between crankcase and heads that has to be dealt with? They are definitely connected by large enough oil drain passages to allow any instantaneous surge to quickly equalize. Is there something I am missing?

That's something I never really understood. The best guess I've got is that if the crank breather can't relieve the blow-by pressure in the crankcase, that pressure pushes oil into the heads and exasperates the issue with oil coming out the valve breathers as the valve breathers end up taking the "overflow" pressure from the crank.

By keeping the valve breather lines smaller than the crank breather line, apparently that helps keep the "path of least resistance" out the crank breather. But I'm not so sure I believe the science behind that theory.

[knucklesplitter]

My testing has shown that there is quite a bit of oil being ingested through the PVC valve also. So it is arguable that the Subaru turbo engines needs 3 catch cans.