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.

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 :-)

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

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

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?

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.

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

Xklaba, starting to understand I think.. Although I can't imagine that much back pressure. It is 4" all the way through to a tiny back box and doesn't have any cats. Maybe I'm still a little confused but am I wrong in thinking that the gases should be escaping through the PCV valve?

That is correct except for the reasoning behind why the gases aren't being sucked out. They aren't being sucked out because any suction closes the PCV valve, which surely can't be right?? and I believe that's why oil is going out the dipstickbut I can't understand why someone clever enough to build an engine and set up all the timings etc would fit a Venturi to a valve that never releases any positive pressure from the crankcase. It seems to me like if a Venturi is being used, then a PCV valve is not the correct valve to use. I am not advocating for or against the use of Venturi to create negative pressure, nor am I saying I will keep this solution, but if this setup, in theory, were supposed to work, how would having a PCV valve connected do anything if it only opens on positive pressure from the exhaust side, for which there never will be any because of the one way valve not allowing any exhaust gases through. The tube that connects to the PCV in this setup is always under vacuum. The Venturi is creating good suction at idle and even more as the rpm increases which implies to me that all PCV valve will never be open.

Xgtrx, no, positive pressure from the exhaust never reaches the PCV because of the one way valve. My original post shows the valve that stops any exhaust gases travelling back up. If exhaust gases were getting up, they would actually open the PCV valve which is what I don't really understand and I the opposite case of what I've been asking about

Hey, So, this is where the PCV is connected to; straight off the end of the black pipe that comes from the intake cam breather. I thought that's the valve cover not the intake manifold. I have an Apexi Power FC ECU; I do a lot of the tuning myself and with the original owner but I'm ok with the tuning aspect; I built my own det cans and have the AFRs at 11.5 on boost with 12 coming on to boost. I run idle at around 13.9 as the cams don't take idling at 14.7. The ignition timing is a bit more convoluted to explain but that should be good too. The CAS is set by the original owner and I haven't touched that and the boost controller is a greddy protecB that I manage the boost with.

Okay right, so I have custom intake and exhaust cams on this car! (TODA 264 9.3mm). Currently with the operation of the PCV valve though, if the positive pressure inside the crankcase is higher, the valve remains shut? because that's currently what happens if I simulate the effect by blowing on the side with the screw

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?

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.

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.

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.

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. 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?

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.

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.

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

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.