Catch can plumbing
 

I've read a tonne of posts on various forums, and I'm just confusing myself a bit - so I'm looking for some clarification.

I've just bought a CDF 3-Port can, with a fourth port for the breather outlet.

From what I understand, my two head breathers 'T' together in the black metal tubing in front of my TMIC:

https://lh4.googleusercontent.com/-Y...907_181218.jpg

So what I'd do is remove that black metal tubing from the car, and run each head breather into a separate port on the can. I'd then blank off the port on the intake hose which the metal T previously vented into.

Then comes the third input from the crankcase breather. I've read a couple of different approaches:

1) Blank off the PCV valve, and run the crankcase breather direct to the catch can, and also blank off the intake.

2) Blank off the intake hose, but leave the PCV plumbed in - and then run the hose into the catch-can AFTER the PCV.

The outlet breather hose from the can simply VTA.

If I understand right, the PCV only "sucks" when the car is off boost - so even when there is minimal crank pressure, the nasty stuff is still getting sucked out. If I blank it, I lose that off-boost sucking - but I also don't get the nasties being blown into my inlet manifold when ON boost which dilutes my AFR etc.

Is it really fine to run the crankcase breather with zero vacuum, or should I keep the PCV valve in place?

Thanks all. 2005 STI if it matters...

there are two basic options
1) the catch can is fitted so it interupts the standard breather system, PCV retained.
all pipes feed from heads/crankcase via catch can back to turbo inlet, no other change to pipework.
2) the PCV is blanked, all pipes, one from crankcase, one from the combined heads, run to catch can, the outlet of which either vents to atmosphere or run back to sump.
The latter is best for track work, No1 is better for the engine on a fast road car.
In my experience the head breather produces 0, the crankcase breather quite a lot on launch starts but this is just my car.
Trev

Don't vent the can back to the inlet as some oily vapours will be going into the inlet as the can doesn't quite catch it all. VTA is best, run the vent under the car & leave the pipe open with NO filter on it as they can get blocked. Some keep the PCV but Iv got rid of mine as I don't want any oily vapours going into my inlet, there are arguments for both though.

Thanks guys, I guess I've been looking for a "what's best/safest" and there just isn't one - seems to be varying opinions at both sides.

My is a daily, and drives 7 miles to work each day off boost - so with that in mind my PCV does a lot of sucking.

So I guess the question is what's worse? Oily vapour in my Intake Manifold or no vacuum pressure on the crank breather?

Oh and I'm pretty much settled on VTA, as surely the existing return to intake pipes are essentially unmetered air (they're after the MAF) so blanking them off can only be a good thing(?)

Hi mate, I fitted my cdf can not long ago. Both heads, into a port each on the can.
I remvoed the 't' piece from the crankcase breather under the turbo. Blanked the pcv and run a hose direct from the crankcase to the last port of the can.

Just to give you a warning, after 600 miles and a mapping session. The breather filter blocked up and blew the o ring clean off the lid of the can! Some extreme pressure there! I cut the filter off bought a new o ring and its currently vta at the min until I get time to route some hose under the car to get the oil fumes away from my cabin air intake.

Thanks Dan!

I'll get an extra bit of hose then to chuck the fumes out behind me somewhere :D