Thread: Crank Case Ventilation fully explained. (Turbocharged edition.)

I've had 0 luck using exhaust scavenging vacuum on my turbo G20. This is using one of the muscle car kits with anti-reverse valve and angled nipple for it.

jannn, those guys with the extra port on the top of their valve covers did so because of serious vertical loads they had to deal with (negative Gs due to steep falling track lines like the corkscrew at Leguna Seca) which they used to keep the oil inside the valve cover. That shouldn't be needed in your situation I wouldn't think.

With a properly working stock setup if you're seeing lots of blow-by you might be better off addressing your ring seal issues.

At the most, I would just route your current catch can to your intake instead of atmosphere. Simple, easy, effective, and most of the work is already done. It's at least something worth trying before you go modifying the valve cover.

Hey! and thank you guys i gave up e-vac exhaust system because it just does not work and end up to do almost to the original setup here is the picture.. i think this will be work very properly!

I believe the exhaust system doesnt work for most b/c its got to be setup a certain way for the venturi effect to work properly

Yes, I've seen directions online for installing the exhaust probe pipe backwards! I think this is the main issue people have when they use a probe instead of just flush-mounting the pipe. The outlet should face the direction of flow, not face into it.

It's also a good idea to swivel the probe with the engine idling to figure out which angle gets you the best vaccuum. A gauge can be used or even just going by feel with your thumb covering the probe inlet. Do this before committing to a mounting angle and rotation.

As mentioned in my NA thread bump, I've been reading up a lot on the PCV and blow-by function for my Subaru's and came across some interesting things that may help us turbo SR20 guys too.

Here a diagram of the PCV and breather function for 2005 Legacy GT (this applies to all EJ255/EJ257 motors too).


Basically when the PCV valve closes due to positive plenum pressure, the crankcase continues to vent to the turbo intake/inlet (intake duct). Since turbo intake/inlet vacuum is fairly low it's hard for it evacuate the positive pressure in the crankcase through just one 5/8" hose, additional venting points might prove useful (DSM guys tend to put extra valve cover breathers to help with this).

Just food for thought

Yah, same thing Fred Cooke did on his Mazda engine which is linked in the N/A thread.

Good thread, but that is talking about turbo application, not seeing any NA references or teeing PCV to intake plumbing?

I've had a couple of catch can setups on my GTiR motor but am still looking for a permanent solution.

Currently ive got this:





PCV-check valve removed (seems to work ok)
stock oil separator removed
AN -8 hoses from rocker cover to catch can
hose from block to now-removed stock oil separator used as a drain for the catch can.

It solved my blow-by issues but the fabricator who whipped it up put the filter sideways, so occasionally surrounding areas have a very fine film of oil on them... so im building a new catch can and moving it elsewhere.
my question: can the hose that leads to the block be used as a drain? or will it just push the oil back into the catch can? This is for a track car, but ideally I dont want to have to drain it.

Looks can be deceiving.
You'd be much better off with a dedicated oil separator and running it to the intake plenum.
Although on a dedicated track car, maybe that is not so important.


Why not modify what you have to point the filter up?


Yes, it can be used as a drain. The stock system uses it as a drain, and it looks like your current setup also uses it as a drain as well.