My Breather Setup

[edizio]

Hey guys,

This is my first post so and I feel a bit awkward using it to ask a question but.. I've recently bought my first GTR R33 and things seems great, the drive-ability etc but there is something that is REALLY confusing me.

How on earth is my PCV system setup? I've drawn a picture below: -

As you can see, the catch can/breather is plumbed into the oil dip stick and the PCV valve that sits in the centre on the air intake side no longer goes back into the intake but goes directly to the rocker cover breathers and then out to a venturi port.

The venturi port creates the vacuum that sucks on the tubing that routes to the PCV valve however upon inspecting, any kind of hard suction on the PCV valve from the exhaust side causes it to shut whereas any suction from the other side caues it to open.

How is this working to allow the crankcase gases to escape? I'm noticing a problem because the oil is coming out of the dip stick feed which implies that the ventilation is not working properly.

[89CAL]

Oh dear...... I'm no GTR expert but seems like someone was trying to hide a problem or really had no idea

I'll let someone with a GTR comment in case the setup is slightly different to GTS-T, but not much about that looks right

[edizio]

It's definitely concerning because I'm getting quite a lot of oil in the catch can shown in the diagram after a pull on high boost.

It's probably worth me noting that I did a compression test and everything is perfect, 168-170 across all 6 cylinders

[XKLABA]

Have you got an actual picture of the Venturi setup ?

The factory setup goes - PCV then hose to cam cover - hose from cam cover to cam cover - hose from cam cover to inlet pipe of rear turbo

The PCV is set right, it is suppose to work when the engine is under vacuum and close when engine sees boost at which point the other end draws the gases out of the crank case breathers, so going off what you have discribed the venturi will be doing what the rear turbo is supose to, this will mean you will get blue smoke under full boost situations and be losing oil

So other then the Venturi setup the rest is as per factory

Also pic of catch can if you can but no line from block should go directly to catch can as it will just pump oil out so disconnect that and put dip stick back in

[edizio]

Hey thank for the reply. The Venturi port in the exhaust looks like this: -

http://i27.photobucket.com/albums/c190/huseinholland/CarMods/IMG_0836.jpg

This connects directly to the PCV valve and cam cover breathers on the rocker cover.

There is no connection to the inlet any more and does not go through the catch can. It's exactly set up as I've drawn in the diagram. I can get some shots of the car bay to show you when I'm on the computer, but as you say, directly connected to the dip stick tube. To be honest I typically understand how it usually works and how people tend to set it up but this set up is weird and I'm trying to understand what it is or was trying to achieve.

I'm not sure what you mean by draws the gases out of the crank case breathers. Where are these? I didn't realise the rb26 had crankcase breathers.

[KiwiRS4T]

Turn the one way valve around. It doesn't make sense the way it is. But monitor it - you may get heaps of smoke out the exhaust! I must admit I have thought of using a venturi in the exhaust to create negative crankcase pressure but have a look at the oil control thread (well maybe the lst 10 pages or so).

http://www.skylinesaustralia.com/forums/topic/110680-oil-control-in-rbs-for-circuit-drag-or-drift/?&hl=sk+oil+control

[GTSBoy]

Exhaust venturis are, um, not real bright. Welcome to the 1960s.

[89CAL]

Venturi seems silly when the intake pipe always has a vacuum

And yeah I'm not real sure why they plumbed the dipstick tube into the catch can. The only thing that worries me is that it may have been blowing the dipstick out which may have caused them to mask it with a catch can. Still put the dipstick in and see what happens. If all is well then you can probably rip the catch can out. If not Then go from there and plumb the catch can up properly

[XKLABA]

While in theory the exhaust Venturi should work in practise on a turbo engine ( depending on where it is located ) it will not

You will be better off putting it back to factory or do a proper breathing setup

The thread Bob linked is a good read

The crank case breaths through the head and out the cam covers

[edizio]

Putting it back into the intake is apparently not a good idea according to some. The car is tuned to the wideband AFR and putting back in oil mist air could lean out the ratios to the point of DET.

I understand from reading that a lot of you do not like the Venturi setup and for good reasons however, I'm just trying to understand what this setup was trying to do. I've taken the tubing off that connects to the PCV and found that even at idle there is a suction from that tube and when revving without even boosting this suction gets very much stronger. The port is on the down pipe which is 4" and the car is running a single turbo setup.

Massive apologies for being so dumb, but I still can't get it through my head how a valve that sits on the valve cover that only opens when air is blown into the engine (which cannot happen, as per the diagram, as exhaust gas will never reach due to the one way valve). When air is sucked from the engine because either the Venturi is creating suction or the crankcase is closed, the PCV is shut. The way I see it, only the rocker cover breathers are ever getting suction from the Venturi. The crankcase can only ever be breathing through the dip stick tube.

I would like to remove the catch can on the dip stick, I find that rubbish and the reasoning is probably that the dip stick was getting blown out due to the pressure on the crank case. The thing is the car is very well looked after and I have pictures of it running the old setup which went back into the intake and the guy mentioned that this is very much more effective at creating negative pressure.

Edited August 17, 2014 by edizio

[Ben C34]

You have missed the part where the rocker covers are attached to the crank case via the engine.

So you think k the setup is good at creating negative pressure, then in the same sentence say the gumby catch can was installed due to pressure build up?

[Ben C34]

And running the blowby into the exhaust isn't legal, so might as well make it a normal vent to atmosphere setup.

[edizio]

Hey, no, if you read the last part, I mentioned that he said this, not I.

I am here for advice because I am NOT sure, if I was sure, I wouldn't be asking, I'd be helping others out with their problems.

I agree that the solution at the moment does not work and that things seem suspicious, so I believe that I'm right in what I'm asking because I have genuinely found a problem with the motor and would like to fix it.

You have missed the part where the rocker covers are attached to the crank case via the engine.

I was under the impression that they were for the cams and that the gases could seep through from the crankcase whereas the PCV connects to a baffle that goes into the crank case. Are you saying that the PCV could just be blocked off in this circumstance?

[edizio]

And yes, the right thing to do is to put it back into the intake with a catch can that separates the oil from the gas and plumbs the oil back into the sump. However I'm trying to understand what the hell this current setup was meant to achieve when the PCV valve, at the moment, seems to be pretty useless.

[XKLABA]

I'm guessing he is in Holland so our laws mean nothing really

I would be interested to see how that Venturi setup works when at full noise as the exhaust starts to build back pressure

The problem with the RBs oiling is the blowby gases trying to escape the crank case via the head trapping the oil in the head, by creating to much negative pressure you will be increasing the air flow through the head making matters worse

The crank case breaths though the oil returns from the head and out through the cam covers ( there are no rockers in an RB )

[edizio]

I'm not from Holland and laws are important; again, I intend to fix this, I'm just, once again, trying to understand what this was trying to achieve.

Take a look at the setup from a picture I took: -

Sorry about the size!!

but yeah, the suction is good from the exhaust and only gets stronger but the way I see it, the PCV could just be blocked off because any suction just closes it. All the work is going through the rocker cover breathers which seems a bit strange.

[89CAL]

I still think plumb it into the intake. It's how Nissan designed it and how it should be. If the engine is healthy then you shouldnt be throwing oil in the system, if the engine is not healthy or is resonably worked, then it probably needs a catch can anyway.

The exhaust venturi is something I have never seen on an RB. Seem's really odd. And as above, the system will not work in venting the heads at high boost when there is exhaust back-pressure (unless you have a 3.5" or greater exhasut with no mufflers/cat). I'm not entirely sure if this will make a great deal of difference but anyway.

I run mine plumbed into the intake pipe, no problems, mines tuned, doesn't lean out.

[edizio]

The current system is a 4" straight through, so not emissions friendly there either.

The car is quite highly tuned, previously on the dyno it had 700hp on the wheels with the smaller turbo on it. Engine is fully forged and specced according to his design. There's pictures of him actually building it with it in pieces so it's all very confusing as to why exactly he would do something like this that seems, to you guys, an obvious mistake.

It's now running a GT4294R turbo and he estimates it to be around 850hp on max boost. It spools very quickly and feels very very quick but I have the boost controller set to 1.0bar for the road as opposed to 2.2. The list of modifications to the oil system is huge along with that to the fuel list too.

He said that the oil mist going in would make it lean and could cause DET if running at high power levels so this is a good way of venting the system.

This still doesn't explain to me why the vacuum should cause the PCV to shut although it seems the actual valve is behaving as it should.

[XKLABA]

The PVC is a differential valve, when ever the pressure on the out side is higher then on the inside it will open, this usually when the engine is in vacuum and it will draw the oily gases into the intake, the Venturi system is to try and keep the pressure on the outside lower then the inside so the PCV never opens and given you have a full 4" with no restrictions I'd say that is what happens, for piece of mind if it was my car I would like to see how it was working at full noise, but that is answered by the catch can, if the Venturi system was working properly at full noise the catch can should never see oil go into it there should also be no need for that catch can

A properly setup catch can arrangement will stop the oily mist getting to the intake

Just out of curiosity where are you located ?

[edizio]

Hey, I'm in the UK actually. Emissions for the UK are actually strange; pre 1995, as long as the car isn't above a specific value from a generic book, it's fine without the catalytic converter. The car passed without it on at the last time but this doesn't mean I'm happy with the solution as it may be problematic if I go to other countries in the EU and it's not really environmentally friendly.

Your explanation of the PCV is making sense to me; however in this scenario, wouldn't the PCV still be closed even though the crankcase is under positive pressure: -

I'm driving hard on boost - Positive pressure in crank case causing the PCV, negative pressure from the venturi in the pipe leading to the valve. In this scenario, I would expect the valve to be shut but shouldn't it be open to vent the crank case so that the blow by isn't just venting out of the catch tank - it obviously has no where else to go does it?

So, I then take my foot off the gas and theoretically I should be in a vacuum/negative but the crankcase won't have vented because it has no where to go so. I then have very little suction (well a little bit), from the venturi port and still positive pressure which means the port is still closed...

This is what I don't understand

This is the PCV valve that the venturi port connects to:

Now, I see that in some race car setups, they actually have a vacuum pump; even in this scenario, isn't the PCV still always just closed?