My Breather Setup

[edizio]

Just to note, I have twin screamer pipes off the waste gates

[Badgaz]

FWIW The pcv is only evacuating blow by that is on idle/cruise i.e vacuum....when putting more pressure in the crankcase by way of rpm and boost the cam breathers are doing the most ventilation.....just plug up the pcv valve and use the cam cover breathers to a catch can if you have no legal issues with emissions control.

[edizio]

Ohhhhhhh!! I understand!

So all this time I was concerned that the suction would cause the PCV to shut but actually the ventilation whilst on boost was never through the PCV valve at all!!!!

So if I'm blowing oil out of the dip stick, there's a problem with the Venturi not creating enough suction on the exhaust cam cover breather given that there is exhaust back pressure. Right so now to fix!

This is a really good community, I'm grateful for your help and understanding in me being pretty oblivious to this part of the engine management.

Edited August 18, 2014 by edizio

[Badgaz]

yes but what you'll find is only having 1 venturi or flute to try and create enough vacuum to remove the crank case pressure is not enough and why the pressure is building in the crankcase and popping out the dipstick. There are 2 breathers off the top of the cam covers....you need at least this piping volume to evacuate the crankcase pressure, on factory setup they join them and plum them into the intake in front of the turbo which creates the vacuum necessary and also meets the emission controls for being legal.

[XGTRX]

Right so now to fix!

.

Try this, cam cover vent to catch can

[edizio]

Ok, so why vent to atmosphere when I could plumb up the dip stick with a one way valve so that it could breath in but not out and then let the vapour exit all through the cam cover breathers?

Or is this going to become a problem, once again, due to back pressure?

[89CAL]

Don't you want to be able to check your oil with the dipstick?

Using the cam cover fittings is what everyone does

[edizio]

I typically just pull the catch tank tube off and stick the dip stick in... Which is a pain because I check the oil before and after I go for a drive!

The car only comes out on nice days.. I use my motorbike or other car otherwise. She's too nice! And too quick lol

[XGTRX]

Ok, so why vent to atmosphere when I could plumb up the dip stick with a one way valve so that it could breath in but not out and then let the vapour exit all through the cam cover breathers?

Or is this going to become a problem, once again, due to back pressure?

Because you really don't know what your exhaust pressure is. If you are venting to atmosphere you do know what the pressure is. Also by an additional venting point you are equalizing the engine pressure and not relying on one point of relief.

At the end of the day whatever you have now isn't working very well. So maybe just try what has suggested and see how it goes. Sometimes you just have to do what's been proven to work and not get into the paralysis by analysis trap which sometimes we are all guilty of.

[edizio]

Hey guys, so an update!

I spoke to the car builder and he said that I could go atmos but the Venturi always worked for him and he never saw oil coming out as the suction was always sufficient so perhaps I should investigate further due to this being odd behaviour

So upon investigation, I found that I had a leak in the half moon seal on the exhaust side where oil seems to be leaking out so I've ordered a new half moon, cam cover gasket and bolt seals. I'm pretty certain that a leak in the cam cover would result in some funny behaviour so I am going to investigate a bit further.

His advice is that if I want to go to atmosphere, like you guys recommend, I'll need 2x 12AN hoses to be sufficient enough to vent.

I'll wait until the parts come and fix the car myself and then see what the behaviour is like.

PS, red metallic rb26 rocker cover with old and ugly breather hoses. What colour samco hoses would look nice! I'm totally crap when it comes to things like this, which is evident because I'm thinking purple!! Lol

[Ryno]

I personally like stainless braid, but go with whatever makes you happy as you'll be the only one that sees it.

This is what my engine looks like...

[edizio]

That looks great, I've actually got stainless braid for my fuel lines and for the exhaust Venturi but standard rubber on the breathers at the moment. Quite tempting! I'll keep posted on what I decide and take some pictures.

It'll be within the next week or two that I fix the leak so I'll probably order something in once I decide what I am going to do :-)

[GTSBoy]

Seriously. Throw away all that crap that is on there now and build a breather system based on the summaries towards the end of the oil control thread.

Edited August 20, 2014 by GTSBoy

[KiwiRS4T]

I personally like stainless braid, but go with whatever makes you happy as you'll be the only one that sees it.

This is what my engine looks like...

Very nice. I like braided lines but I use rubber hose cause I'm poor. BTW what kind of plenum is that?

[jjman]

Hey guys, so an update!

I spoke to the car builder and he said that I could go atmos but the Venturi always worked for him and he never saw oil coming out as the suction was always sufficient so perhaps I should investigate further due to this being odd behaviour

So upon investigation, I found that I had a leak in the half moon seal on the exhaust side where oil seems to be leaking out so I've ordered a new half moon, cam cover gasket and bolt seals. I'm pretty certain that a leak in the cam cover would result in some funny behaviour so I am going to investigate a bit further.

His advice is that if I want to go to atmosphere, like you guys recommend, I'll need 2x 12AN hoses to be sufficient enough to vent.

I'll wait until the parts come and fix the car myself and then see what the behaviour is like.

PS, red metallic rb26 rocker cover with old and ugly breather hoses. What colour samco hoses would look nice! I'm totally crap when it comes to things like this, which is evident because I'm thinking purple!! Lol

Im thinking the reason that you perhaps have the leak out of the half moon seal is the setup you have pressurized the cam covers with your current setup

Just vent atmo (including blocking the PCV valve) in a subtle way and be done with it. E.g. just like Ryno's setup above. The hose coming out of the can can go down to breathe out below the car (but made to look like it is going somewhere legit in case the 5-0 has a brief look under the bonnet...)

Edited August 20, 2014 by jjman

[edizio]

Pressurising the cam covers doesn't sound good. That would imply that I'm getting positive pressure from the exhaust wouldn't it? Which is weird because I tested the one way valve to make sure no exhaust enters the system..

Chances are I'm going to go with the atmo setup with the 2 12AN lines like you guys recommend, it doesn't look hard to set up either. It's a shame though, as you guys write, in theory the Venturi system seems like it should work.

[GTSBoy]

No, the engine itself pressurises the cam covers (which are in the same volume as the sump!) by blow-by past the rings. That's why you have to have a breather system at all. The PCV system cannot suck the crankcase gases into the intake manifold under thos circumstances because there is boost in there.

And to make matters worse, the one way valve in your exhaust venturi is set up to prevent any flow from ever going out to the exhaust, so even if it could suck the crankcase gases out (assuming the venturi works) then it won't.

That's why none of this silly circus works. Piss it all off, start again.

[edizio]

Yes, will probably replace the system :-)

Although! The one way valve should only be letting gases go back down into the exhaust and not up into it. Didn't quite understand what you said there

[Ryno]

Very nice. I like braided lines but I use rubber hose cause I'm poor. BTW what kind of plenum is that?

If you look closely you will see the engine is a RB25DET, the plenum top was made by MX Performance in Sydney... I'm not sure if he's still in business (as I can't find his website anymore) however I'm really happy with it - similar quality to Plazmaman and a little better price wise. I also run a MX Performance exhaust manifold, it has 1" runners and spools the turbo much earlier than the stock manifold.

[GTSBoy]

Yes, will probably replace the system :-)

Although! The one way valve should only be letting gases go back down into the exhaust and not up into it. Didn't quite understand what you said there

I quote from your original post.....

"any kind of hard suction on the PCV valve from the exhaust side causes it to shut"

I read that to mean that the one way valve will not permit flow in the direction engine -> exhaust and will only permist flow in the direction exhaust->engine, which is of course the wrong way around, which has already been said by somebody earlier on in this thread.

So when you are on boost you have nowhere for crankcase gases to go at all. The PCV connection at the intake manifold will only suck on the crankcase when the engine has vacuum, and the venturi will NEVER suck on the engine.