Catchcan plumbing question...

[Ronin 09]

OK I searched, and read the whole of the "catchcans what's the deal?" thread.

I couldn't find the answer to my question, which is quite simple, so bear with me.

I got a Hybrid Oil Catch can and installed it on the weekend. Basically, the rocker covers are still connected, one hose runs from the rocker cover breather to the catch can. The can came with a blanking plug, so you can install a hose from the can back to the intake that does not work.

My question is this - by my thinking the rocker covers are not venting, and basically the hose from the rocker cover to the intake will flow all the gas. Thus the can is doing nothing. Secondly, will there by a build up of pressure in the head because the catch can does not vent back to the intake?

[JimX]

My cheapie can also came with a blanking plug, and from what I can tell the blanking plug is not meant to be a blanking plug! I had it swapped with another plug with a hole, which is what I believe it's meant to be. This is so the crank case gases flow out of the rocker covers, through the can where the oil can condense, and then back into the intake again without any oil. Looking at the translucent lines of each it seems to be working well. Very little crap on the exhaust line and none at all on the intake.

Yes there will be a buildup of pressure in the can unless you have one of those venting caps, and I don't know how dangerous this is because I don't know how easily it escapes. When I was fitting mine (with no venting cap) I took the drain plug off the bottom and put my finger over it. At idle it was trying to slowly suck my finger up into the can. I didn't rev it but I imagine that under revs it would blow it back out again. That means pressure both ways and I don't think it easily cancels out.

What I would do if you can't swap the blanking plug for one with a hole is to just drill a hole in the blanking plug, then fit it all up as before.

Oh, of course if you do have a venting cap as many (illegal) cans do, then you don't need to feed the intake back at all. Just leave it with the blanking plug for the cops to see if they pop your bonnet. Although they may spot the breather and do you for it anyway.

[Ronin 09]

Thanks for that answer Jimx, I suspected that it should be open back to the intake side. I'll try and source a new plug, but I was going to drill out the blanking plug otherwise.

cheers mate

[Steve]

......I took the drain plug off the bottom and put my finger over it. At idle it was trying to slowly suck my finger up into the can. I didn't rev it but I imagine that under revs it would blow it back out again. That means pressure both ways and I don't think it easily cancels out.

.....

Sounds like its time to block your PCV valve.

[JimX]

What's blocking the PCV valve do again? I know you've mentioned it in the past but I forget

[Steve]

under normal vacuum, the pcv will suck air and fumes from the rocker cover into the plenum, under boost is should seal shut causing the fumes to have to exit via the catch can.

If you block it you have 2 advantages:

1. no crank case gasses will go into the plenum, they must exit via the catch can only.

2. under vacuum there is no air leaking around the throttle body, under boost you dont loose any boost pressure.

Even a small leak through the pcv valve can make a noticeable difference to how the car feels at idle, part throttle and WOT. I brought my boost threshold back by around 500rpm (GT30 turbo) and also tidied up the idle heaps (it was sucking at idle) by blocking mine.

[JimX]

Ah right. There's no hose connecting the rocker covers to the plenum at present that I recall. There's one line which is blocked off on the plenum, which could have gone to the crank case originally. I'll have to take another look.

[Skyrine-Dave]

what does it mean when oil starts to spray out the dip stick under boost ?

[Sydneykid]

Hi Guys, We use a catch can vented to atmosphere with a small air filter on top, this reduces the smell a lot. The catch can has two inlets, one from each rocker cover. We replaced the PVC valve on the inlet manifold (plenum) with a bolt and blocked off the inlet in the air feed to the turbo.

Blacking off the inlet in the air feed to the turbo stops oil fumes getting into the inlet and filling up the intercooler with oil. Which, over time, reduces its efficiency. Some oil mist also gets into the engine and causes detonation. This happens when the car is on boost.

Replacing the PVC valve with a bolt stops the oil fumes getting into the engine via the PVC valve. This oil carbons up the combustion chamber and fouls the plugs. This happens when the car is not on boost. This also causes it to detonate when you get back on the throttle.

Hope that contributes to the knowledge bank.

[Steve]

what does it mean when oil starts to spray out the dip stick under boost ?

this is bad, your crank case is pressurising. You either have massive blowby (gasses that go around the pistons when the a/f mixture is ignited) or your crankcase gasses are not being allowed to vent.

You need to check if your PCV, or catch can (if fitted) is operating correctly. If it is, its a good indication that your engine is quite tired.

One check to do is to remove the oil filler cap. You should be able to feel gasses coming out, gently, at idle. If the gasses are coming out fast (like being blown out by a fan), your rings are tired. If no gasses are coming out, you could have a blockage in the line that links the bottom end to the head (not sure where this is on an RB engine, anyone?).

If you are not sure, just give the engine a little rev - this should increase the amount the engine 'breathes' through the rocker cover. Even if the engine breathes a fair bit, you may still get a decent life out of it, no guarantees though.

Also, you need to check thoroughly that the PCV ventilation can actually go somewhere, and is not blocked off as discussed above.

Hope that makes sense.

[R31 POWER]

See if someone can help.

Ok I have a bolt in where the pvc valve was and 2 hoses coming from the rocker to a catch can.Can this cause the idle to drop and want to stall sometimes.

[knore]

I think someone needs to make a definative way to setup catch cans on R33s etc

I got a trust can today, im just putting the left and right rocker hoses to the catch can and blocking the left over pipe that goes down towards the turbo

Im assuming this is right

[jay.r33]

hi guys is it possible to get some pics showing the correct way to install the catch can thanks

[riceline]

Hey guys... Just nocked up this little image in Paint to try and help figure this out...

From what I can gather..

The Blue and yellow ones hook up to either side of the oil air catch can (vented one of cause) and the Red one (that usally goes to the inlet pipe before the turbo gets blocked off)

Is this right guys?

hope this helps.

[RYanR31]

perhaps a non vented can, one hose from each rocker cover to the catch can(or use the standard cross over pipe and use the third pipe to go to catch can), another hose from the can to the intake so the oil is caught by the can before it goes into the intake, and blocked off PCV. this will keep the system enclosed and will keep the idle stable without it breathing through a filter on the catch can. This will enable the same sort of setup but with a catch can in the middle to catch the oil. (obviously)

[riceline]

hmm thats not a bad idea..

thing is.. what is the PCV?

and what you are asying (using my little image )

the blue and yellow hook up normaly. The red one goes to one of the inlets on the catch can and the other to the inlet pipe.

thing that I was wondering.. I was hoping to change the pipe from the AFM to the turbo to a metal (stainless) one. How would this be set up?

[RYanR31]

yea the way you said it is the way i said, you can just change that pipe between the turbo and the AFm because the pipe that usually goes to the pipe from the rocker cover wont be needed anyways so yea. you can either keep the standard pipe going between the rocker covers and use the 3rd pipe to run ONE pipe to the catch can or you can run two seperate ones and block off the 3rd, then run the intake pipe to the unvented catch can. The PCV valve is on the drivers side of the drivers side rocker cover and is a one way check valve which doesnt allow boost to pressurise the crank case. this can be blocked off. i think the intake pipe is also a PCV valve.

[Sydneykid]

Hey guys... Just nocked up this little image in Paint to try and help figure this out...

 

From what I can gather..

The Blue and yellow ones hook up to either side of the oil air catch can (vented one of cause) and the Red one (that usally goes to the inlet pipe before the turbo gets blocked off)

 

Is this right guys?  

hope this helps.

Hi Riceline, in your picture you cut off the 4th connection, the one that goes to the PCV valve on the plenum. It is on the cam cover juts down from the blue one in your picture.

If you open up the angle of the photo a bit so we can see the inlet plenum, then I can draw on your picture the choices you have for plumbing up a catch can. Yes that's right you have CHOICES, there is not a wrong and a right.

[WLD747]

Anyone got a pic of this done correctly.

[Trust33]

Cool stuff i never new untill now what way to do it.