Catch can

[presterone]

In the valve cover It looks like there is a flapper plate that lifts up when engine vacuum is applied (intake manifold side of VC) so if I run lines from both nipples of the valve cover straight to a catch can, will it not vent PCV at idle or something?

 

[JNR]

You could, but what would you use for vacuum to have a working PCV system? I mean, the purpose is to pull out the gasses and reburn them, so if you take out the PCV valve, you would not have any working vacuum to pull them out. If you recirc'd it back to the intake tube, I suppose there may be enough vacuum from the air being pulled into the turbo (inlet), but not sure it'd be as effective.

What you could do instead is just run the line that comes off the (pass.) side of the valve cover thru a ctach can, and back to the air inlet tube (pre-turbo), so when you're under boost it will "filter" out the residue, but let the air go back thru the system; under n/a (vacuum) conditions, that same nipple acts as fresh air for the PCV system, where it takes metered air (pre-turbo).

Keep the PCV valve and you could run another (separate) catch can from that valve to the intake manifold (will need check valve on out side of can though so the can doesn't get pressurized), or at the minimum run a low crack pressure plastic inline check-valve so when under boost it can't go back thruthe valve (it's possible with an oem PCV valve only that some (pressure) will go back into the valve cover baffled area.

EDIT - here's an excellent article on how it works and how you can install catch can(s), particularly on the 4G63T

 

[Okayplayer]

In most of the examples in the link you provided, it shows multiple catch cans. I have a JB fab catch can with a breather on top. Would it be necessary to hook to some vac source in order to maximize it's use? I used a hollowed out pcv in the stock location to one side of the breather, and the other goes to the nipple on the passenger side of the valve cover. Am I wrong?? /ubbthreads/images/graemlins/uhh.gif

 

[JNR]

I guess I don't see the reason/benefit to have a breather on the top of the catch can on a turbo system, since the air inlet of the PCV (the oem hard 90 deg nipple off VC) also acts as a 'return' to the air intake tube (pre-turbo) under boost conditions...If (on a N/A setup) you were to put a small air filter on that PCV inlet tube, it *works*, but on a MAF system there is some unmetered air then, although it's pretty small; I did this on my GTO, fwiw, and ran a [sealed] catch can in-between the PCV valve and intake manifold inlet nipple...if it were turbo/supercharged, however, I would need a check valve that would only allow flow under vacuum and not under pressure.

The PO in his infinite wisdom simply installed a small ricer filter off the 90 deg tube on VC and needless to say it go soaked with crap (when it was under boost) and popped my dipstick, as it had nowhere to go, for the most part. IMO, this would be the same thing with a filter on the catch can, but may work only a little better since it wouldn't get so filled with crap (the filter) if the CC worked properly.

If you're only going to run one CC, do it on the line between the VC and air intake tube and have it sealed (no filter).

Really the *only* purpose of a catch can is to act as a filter for the air (gasses) that have 'contaminents' in it, so it doesn't get in your turbo compressor wheel, IC and it's tubing, or intake manifold/CC...Just think of it as an inline filter on those lines and you can see why a air filter won't work properly, since it then "opens" up that line, if that makes sense.

 

[Okayplayer]

So basically in a turbo set up, it only works well if it has a vacuum source to draw the oil rich air into the can. Makes sense, I wonder what difference this will make...

 

[presterone]

JNR thank you for the link it was very informative. I have never really questioned the Catch can Idea because I have never had a use for one, but I am running more boost than stock through a larger turbo so I figured this twenty two year old system could use a little tweaking. Also I have a speed density setup so that might help me with my filtered(open to atmosphere) JNZ tuning cheapo catch can?, rather than having to worry about a post MAF air leak.