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Catch Can Install

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Hey guys,

I'm wanting to install a catch can in my car, I've been noticing a bit of oil in my intake, then going through my turbo etc.. I also want to reduce crankcase pressure to help prevent blowing seals, and blow-by, since the chances of this are higher now the car is boosted.

Anyway, I know where the PCV (pressure control valve) and breather tubes are. Now my problem is (I think I've thought about it correctly!!) is that I get oil coming through my breather hose down into the intake pre-turbo. Now, this happens because when I get positive pressure in the intake manifold, the PCV closes, because there's no vacuum to open it, and the positive crankcase pressure (which is a lot higher than normal due to boost) has nowhere to go apart from down the breather tube (which normally SUCKS from the intake, not blows).

Ok, now the issue here I have is: is venting the crankcase pressure through the breather tube (i.e. when boosting) detrimental to the engine? Say, if the PCV was able to be open whilst boosting, would it be better for crankcase pressure to travel that route (in terms of engine life, seals blowing etc), or is it doing no harm going 'backwards' through the breather? If its no worse, then I'd just go for Option 4 (see below), but if that is the case, then they wouldn't have a breather in the 1st place, because all the fumes/oil would just go and get burnt up anyway, since its in the intake tract?

Anyway, I've been told if I want to keep the PCV, then ideally I should find another source of vacuum to keep the PCV open, and it was suggested to use the pre-turbo intake. I don't see how this really makes sense, because I don't see there being ANYWHERE near the amount of vacuum in there, compared to the intake manifold (due to lack of a throttle plate).

I took the hoses off the car temporarily, and noticed that there is positive pressure coming out of the crankcase at idle, do you guys think this would be enough to open the PCV by itself with no idle on the other side? (Remembering the PCV is just a 1 way valve, so vacuum on 1 side, or positive pressure on the other will do the same thing).

I'm just wondering how on earth I should hook up a catch can?

So the options I have thought of are -

Option 1: PCV > catch can > pre-turbo intake, which takes its fresh air source (breather tube) from the intake.

Option 2: Should I just put a breather filter on the breather tube instead? Making it not a fully closed system.

Option 3: Or, go for a fully open system, ditch the PCV, run a catch tank off the old PCV line, with a breather filter on top of the catch can (or somewhere to release the pressure). This makes perfect sense, but then you get the smell associated with it going into the atmosphere, and I HEARD that your oil gets dirtier quicker this way?

Option 4: Or should I do what a lot of people do, and just put a catch can in the breather line, and wait for positive pressure to push oil down the wrong way, like its doing at the moment! That wouldn't do jack on an N/A car anyway.

Man, I've really rambled! I've read heaps of forums about how to do this, and heaps ppl come up with some wacky and different ideas! I hope you guys can comprehend what I'm saying! I should link to a picture of my car (its in the gallery somewhere), so show you where my breather tube is now hooked up, but I'm sure you get the idea when I saw its pre turbo.

Thanks in advance guys! Hope it doesn't rack your brains at all! I hope I got it all wrong, and someone points out the obvious, and makes me look like a fool, cos I'm pretty stumped! There must be an easy way out!



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How about two PCV's Lawrence.

One is in the 'normal' line, from the crankcase to the intake manifold, and lets fumes flow through under suction at idle & no boost.

The other sits between that and the engine, and has a REALLY weak spring so it opens on any positive pressure and vents to a catch tank/atmosphere or the air filter body. (there's really no suction behind an air filter...!)

So when idling or no-boost, the crankcase is scavenged by the first PCV vavle as per normal.

As soon as boost is up the positive pressure in the crank pushes past the second one. So this needs a very weak spring and acts as a one-way valve to stop fresh air being sucked in at idle.

You are right about the lack of venting if the normal system is left in place. The crank pressure will build up from both the extra blow-by and also because the pcv valve is trying to clear INTO the positive pressure inlet manifold. This will blow past the front & rear crank seals.

(How about a dry sump system.... :ph34r: Scavenge everything back to the oil tank in the boot!)

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Thanks Keith, I thought you'd pop in here with an answer!

I have thought about the idea of using more than 1 PCV or check valve. I guess your idea would actually be pretty easy to fabricate up. There's already a bit of puff coming from the crankcase at idle already, so I'm guessing it would be pretty simple rigging up a valve in that fashion!

One more question, if ya don't mind answering it! If you can relieve all the pressure from the crankcase, would blow by cease to come out the breather tube (the one that leads to just after the air filter)? I guess another way of wording it is, is more beneficial for the pressure to come out of the PCV line, rather than the breather (like it is now at WOT)? I'm guessing yes to both questions though, it seems only logical, otherwise there's no reason for the PCV to exist :)

Thanks again Keith...and I don't think I'll be heading the dry sump way yet!! :D



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Yes, if you could catch all the blowby then air would go INTO the engine via the air filter vent tube like it is meant to.

My idea wouldn't work as it it would be easier for the blowby to go to the inlet behind the air filter than out through a valve. I should think more before I type!! :wacko:

See if you can find out what Subaru do for their turbos. I'm sure that as soon as you're on boost the blowby flows up to the tappet cover and down the tube to the air filter. It still get burned, but oil will condense out as you've noticed and form a puddle behind the air filter. Then off boost air flows back the other way and gets sucked through the PCV.

Its not really a problem, you just need to catch the condensate if you don't want oil in the intake system. Some sort of ceramic filter like they use on compressed air lines that drips it nto a jar...

How about you other turbo guys??


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Yea, i'm kinda working thru the same problem at the moment, havn't come up with any solutions tho.

Off the topic - Lawrence - my power fc with hand controller and extension cable turned up today :)

It's going in next Thursday to be fitted and the loom to be wired "back to standard" and the FCU to be taken out. Then it will be going for tuning.


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Corey: Thats awesome mate, it'll be good to see how the results turn out. Have you decided who you are going to get to tune it yet?

Do you know if you can run the car with a map sensor as well? I'm still tossing up whether to keep the microtech or not. My brother is in Japan atm with his wife (who's Japanese), and they've been getting stuff for me. Maybe if the results are good, I can get them to pick me one up before they come home, since she knows people in the performance car business! :) They're already getting me a couple of things :) Nothing that will really surprise you though!

Did you manage to get rid of your Link as well?



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