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

Hey Ben

I have a red top s13, so I do not have the connector on the top right. S14 and S15s have that connection, as apprently their valve cover has some internal baffling, eliminating the need for a factory catch can. There is a company out there who will fuse an S13 with an S14 cover, but thats quite expensive.

The thread on Zilvia (SR Owners... More HP Easy Mod... Catch Can Setup - Page 6 - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum) was designed as an experiment for a cheaper option and apparently itworks, and adds some baffling to the cover:



Currently, on my T piece, the front hose is connected to a catch can, and the rear facing hose is connected to a hard line on the block (is that the crank case)

Cheers

Sorry for the questions, I'm just getting familiar with the RWD setups. I believe I have them all figured out now.

Let me dissect this setup first:


The PCV line on the left looks stock. Good.

The crank case (yes the metal line going to the block) vent goes directly to the catch can.
The valve cover vent goes directly to the catch can.
The catch can vents to atmosphere.

This is essentially identical to a stock setup, except the valve cover vent section has now gone through two oil separators instead of one, the stock restrictor has been removed (an idea I'm liking less and less these days), and the whole shebang is vented to the atmosphere.

It has basically the same pros and cons as this example: http://www.sr20-forum.com/583995-post4.html

Acceptable.

I dont really want to vent to atmosphere as I believe you lose pressure and it compromises ring seal etc? Plus its illegal!

What if it was the same setup as above, but not vented to atmosphere but routed back into the intake?

Also my car doesnt have the stock separator as it was removed by the previous owner. The stainless headers didnt allow enough room for it I think?

Next we will dissect this example:




The PCV line on the left looks stock. That is good.

The crankcase is routed to the valve cover backwards. No big deal.
The valve cover is then vented in a new section added at the back. To where? I have no clue. That is important. With the length of the line, I assume it connects to the intake before the turbo. That would be fucking sweet. Assuming that's what this person did, then this is a pretty decent setup. The only issue is that now plenty of blow-by leaving the valve cover doesn't have many baffles to go through before it vents. Likely a good bit of oil is getting out of the valve cover in the air.

If that line goes to a catch can, that then goes to the intake tube, then he's in even better shape.

If it just vents to atmosphere, then this setup is not good, but totally acceptable. I can see the idea was to remove the stock catch can by using the valve cover instead. In my mind, he should have just connected the crank case to the new bung on the valve cover, and then run the normal valve cover vent to the intake. That would basically mimic the S15 setup, and that would be really nice. Everything would go through the baffles in the valve cover. With a bit of re-arranging of his hoses, he could get there. He is sooo close!

Maybe I'll go sign into Zilvia and help him out.

Venting to atmosphere is bad form all round. Good on you for trying to avoid it.

That would basically mirror a stock setup, except you'd be running the valve cover vent through an extra oil separator. This would be a great way to go if you don't have the stock oil separator anymore and you'd like to mount this catch can elsewhere.

You have my blessing.


If you want to go without a catch can at all, that other example show is a pretty ingenious solution. He just hasn't routed it perfectly.

Upon reading that thread, it seems that those valve covers with the extra bung have some baffle work done inside them. So that changes things a bit depending on how that is done.

Still, that seems unnecessary since you could route things the other way and be golden.

I see the point of that Zilvia thread is to make everything (all the oil) drain back automatically. That is a commendable goal. It is hard to do though, and it is hard to improve on the stock system without doing dramatic things (like weld additional bungs to the valve cover). I still believe that draining things back to the crank case would work just as well if those hoses were swapped as I said.

I see those folks on Zilva have been wondering what those damn restrictors are for as well. =D

And reading further, I see now why he has not done things as I've suggested.



He's racing with large elevation changes, and negative G's so he's trying to vent from the tallest spot possible. He also knows that in the past the main valve cover vent is prone to just spew oil out during extreme maneuvers.

If you are racing on a track with extreme elevation changes possibly with cornering at the same time (Laguna Seca, etc.) then his setup makes perfect sense. If you're just a normal person, you could do with less, or a more traditional setup. =]

Thanks Ben

I do believe it goes from the top of the valve cover through a catch can and then into the intake.

I dont mind welding stuff, or tapping and using epoxy. I also want it to look neat. And in terms of the baffling, its just a few holes that have been drilled to prevent oil from pushed up the AN fitting on the top of the valve cover.

Can you see any benefit of one setup over the other? Unfortunately I don't get to race on tracks like Laguna Seca!

Thanks

I do believe I eventually saw a picture that showed this.

That's a pretty thorough setup then. Very good.

I like the setup with the added bung on the valve cover a lot now that I know it is hooked up to an additional catch can and is plumbed back into the intake. (Don't forget to plumb it in post-MAF.)
It is obviously more effort, and might be more money to do. I do think it is probably the better setup.

The other method is fine too, but maybe not as awesome. Just make sure you also plumb it back into the intake.

Excellent time to bust off the valve cover and get 8AN fittings! Instead of welding do you see any problem with drilling and tapping, then using epoxy?