Has anyone fitted an oil catch can?

[Tlag]

As you may know, Im slowly building a high power engine and it will need a catch can set up. The problem I am having is the plumbing.

 

The short motor is a 2.5 STI block and has two crankcase breather ports, effectively, one in front and one behind the inlet manifold. The heads are Legacy GTB and have one breather port on each head, wheras as the 2.5 avcs heads have 2 on each.

 

The inlet manifold has a PCV valve directly under the throttle body.

 

Catch cans, typically have 2 inlets for dirty air/oil and one outlet to allow the cleaned air back into the turbo inlet pipe. Some catch cans have 3 inlets and one outlet.

 

So, how do I plumb it together? Ive read loads on the various websites and a lot of people have a lot of different opinions but I cant find a definitive answer.

[Gambit]

I've never fitted one but they do look like a pain in the rear hole. I've read they are set up the same way the Imprezas. I'm just looking for more info if it helps. 

[Gambit]

Not sure if any of this will help. 

 

 

 

 

 

I see what you mean it's a bit of a mine field :( 

[Tlag]

Thanks for that Pete. You seem to have discovered the minefield that I'm going through :)

My main issue is that the 2.5's have two vents on the cam covers and the 2.0's only have one. The extra ones are supposed to be to balance the pressures between crankcase and cam covers using the extra vent on the crank case. The question is, what do I do with the extra one on the crank case. So far, I'm still looking.

[Gambit]

You're welcome mate. It is I can't find anything I will keep looking but it's pages among pages of just nothing. :(

Just going to add some bit's might help others or yourself in the future if anyone is going to do it :)

 

How should a catch can be installed?

There are a variety of ways to install a catch can. There's one right way, two sort-of right ways, and some would argue that at least one common installation method which is wrong.

 

Sort of right ways:
1) Disconnect the hose which runs between the PCV valve and the turbo inlet pipe. Run a line from the PCV to the catch can, and another line from the catch can to the turbo inlet hose.

2) Disconnect the hose running between the crank case breather lines and the turbo inlet pipe. Run new hose between the breather line and the catch can and another hose between the can and the inlet pipe.

 

Right way:
Use two catch cans. Configure one as discussed in option one and the other as described in option 2. For optimal effectiveness, this is the way to go.

 

Wrong way:

Disconnect the PCV<->Inlet line as well as the Crank Vent<->Inlet line. "T" the PCV and Crank vent lines together, and run the remaining end of the "T" to a single nipple on the inlet pipe. Cap the remaining nipple on the inlet. You'll be sending boost into places that definitely shouldn't ever see any. Bad idea.

 

Valve cover vent lines? There's more than one?
Yes, but they're T'd into that black tube which runs in front of your intercooler. The third part of the T is a hose running to your inlet pipe.

 

Can't I just vent these lines to atmosphere?

You could indeed, but there are several reasons why you shouldn't.
1) You'll lose the benefit of having the inlet's vacuum help suck filthy air out of your crank case (thanks to Wylde Horses for this one)
2) It's bad for the environment
3) It'll make a mess of your engine compartment.
4) It'd let metered air out of the system

[Jay762]

not fitted one to a car yet but given the amount of stuff that gets put back into the manifold in the name of emissions reduction I can see myself doing one soon - I was looking to adopt the same simple method used on my bikes. Have the vents going to the catch tank only with the tank venting to atmosphere - mounted away from the air intake to the cabin. The oil gets retained and the pressure gets vented to atmosphere.

 

The intake system on the car now just has external air and petrol going to the cylinder heads

 

wrt points 1-4 above

1) what benefit? Also the positive pressure generated in normal engine operation circulates air no problem

2) so is the current industrial revolution happening in China plus cows farting

3) never had that using a catch tank with filter attached to the vent and an internal baffle

4) If you blank the feeds into the manifold and turbo inlet this becomes irrelevant - although Im not convinced of its relevance in its own right.

 

I would start with a simple solution - even if it means two catch tanks to reduce plumbing, blank the intakes and remove the PCV

[Tlag]

I've no objection to two catch tanks.

My main concern is that extra, central crankcase vent. Apparently, a lot of oil goes through it due to it being directly above the crank shaft and un baffled. It's main purpose is to balance the pressures between the crankcase and heads. I can't think of an easy solution to achieve that but I have seen a solution which requires me to have the cam covers drilled and a pipe welded on to each so I can achieve it. Two catch cans would then be an easy solution.

Before I take that option, I want to explore everything else to see if I can resolve it without engineering work.

[Jay762]

Thought - If they are all to atmosphere is that not equal and therefore balanced?

[Tlag]

That sounds about right but....... I would still need to vent the cam covers some how.

[Gambit]

Well I got to a point of going over the same stuff I read so gave up yesterday. I did come across one link sounded promising someone had asked if they had done it to their 2.5 Legacy had a link to it, thought great found exactly what I wanted..... Dead link 

[Tlag]

I keep finding dead links too. :(

I have decided to install extra vent pipes on top of the cam covers. I will then, simply link the new vents to the large un baffled one on the crank case. That will solve that issue and any oil that comes out the crank vent will find its way back into the system.

Next, i will get 2 x two port catch cans. One will be for the original cam cover vents and the other for the baffled crank case vent. This will mean deleting the PCV altogether and making the whole thing simpler.

As I am going front mounted intercooler and deleting the air con, I should have plenty of space to make a tidy installation of the cans.

That's the theory anyway. Any comments or advise greatly appreciated. :)

[Jay762]

I'd stand by that approach - keep it simple :)

[Gambit]

I like the idea and with no air con saves weight and more to the point that you said keeps it tidy :)