Let's Talk Pcv...

[Tony de Wonderful]

Ok so I hear some people say that the RB benefits from positive crankcase ventilation and some say it does not?

So should you just let it breath 'oh naturale', or does it benefit from a bit of -ve pressure to suck out those fumes and blow by?

FYI I couldn't give a monkeys about emissions laws it is purely for the health of the engine.

[GTR_NUTZ]

Yeah man I'm in the same boat. I got a GTR, a little off topic but i want to set up a oil catch can so I don't know if i should block the pcv valve and run the catch can or let it breath and run a catch can OR block/ unblock the pcv and run no catch can. (stock set up)

I've been told people just block it to keep the revs down at idel and numerous things about a RB26 not creating alot of blow by to really worry about any problems. I guess the only reason why it breaths in the first place is just for emission laws.

But if you block it, all that pressure has gotta go somewhere... ie. through seals causing oil leaks. Out the dip stick..

[KiwiRS4T]

I am making a venturi set up attached to my dip stick tube to remove pressure from my crank case. This is a stop gap plan until I can get the engine out to do the proper oil control - smaller oil restrictors and better drains etc. There is a theory that the "drain" some people put at the back of the head actually acts as a breather for the sump and that excessive pressure build up in the crankcase helps tp prevent the oil from draining from the head.

If it works I'll post up pics etc

[Hanaldo]

Was told by a very experienced RB specialist to leave it plumbed in. His 700rwhp RB certainly doesn't have any problems with it...

[GTScotT]

+1 plumb it in.

I dont know a motor that wont benefit from ventilation.

[Tony de Wonderful]

Was told by a very experienced RB specialist to leave it plumbed in. His 700rwhp RB certainly doesn't have any problems with it...

Sure but does he run it through a catch can before it goes to the intake?

[Hanaldo]

Of course.

[Tony de Wonderful]

I am making a venturi set up attached to my dip stick tube to remove pressure from my crank case. This is a stop gap plan until I can get the engine out to do the proper oil control - smaller oil restrictors and better drains etc. There is a theory that the "drain" some people put at the back of the head actually acts as a breather for the sump and that excessive pressure build up in the crankcase helps tp prevent the oil from draining from the head.

If it works I'll post up pics etc

Doesn't the RB crankcase breath through the head with the stock set up? I thought that was the point of the breather system on the rocker covers. I understand that gases coming from the bottom end are competing against oil trying to flow back in the opposite direction, but otoh if you are producing a load of gas then surely you have a busted piston ring at the very least?

[Tony de Wonderful]

Here's a thought. You go from idle to WOT with the recirc system. It puts the head under a bit more -ve pressure compared to idling, the gases in the bottom end try and equalise pressure and so flow up into the head, but this is right when you are wanting to stop build up of oil in the head and that oil is trying to drain down against the flow of gas up caused by your extra -ve pressure? Surely better to leave the head just at atmospheric pressure and the system open?

[JonnoHR31]

closed throttle is when you have the most -ve pressure in standard form as its sucking through the intake manifold, once you go past 0 boost the pcv valve shuts and its sucked through the intake pipe (high flow but not much vacuum).

[KiwiRS4T]

"

Doesn't the RB crankcase breath through the head with the stock set up? I thought that was the point of the breather system on the rocker covers. I understand that gases coming from the bottom end are competing against oil trying to flow back in the opposite direction, but otoh if you are producing a load of gas then surely you have a busted piston ring at the very least? "

No. I have read the 40 page oil control thread twice

http://www.skylinesaustralia.com/forums/topic/110680-oil-control-in-rbs-for-circuit-drag-or-drift/page__hl__sk+oil+control

and it is a problem suffered by others with a new or old engine. It only manifests itself with sustained high revs therefore really only on the track. I had it with my RB25DET and now again with the RB30DET (yes I should have learnt).

You are right about the breathers on the can covers but when the head fills with oil they just fill the catch can with oil (and blow it out elsehere as well). The problem is thought to be worse with RB30s.

There is always some blow by and especially at high boost and revs and the action of the crank is thought to make things worse.

So yes you need to keep your breathers and preferably run them through a catch can and then into the intake for a street car.

[Birth]

Hi guys - for the second time (I should have learnt) I have installed a catch can and blocked the PVC valve. Both times I have. Loan the front crank seal. From now on I think I'll be leaving the PVC valve plumbed in.

It seems likely to me that the blown seal is from too much pressure with the valve removed. Any thoughts?

[bubba]

Did you leave it plumbed to the intake?

If you block the PCV valve you HAVE to run atmo..

[Birth]

I ran a hose from the catch can to the intake pipe before the turbo - I gather this is not what you mean by atmo?

I seem to be the only person on SAU complaining about a blown seal, other people seem to have their dipstick blown out. Poor me.

[bubba]

Ok lets firstly dispell some myths..

All a "catch can" does is catch oil.. requirement for most racing categories (must hold a certain volume) so you don't spew fluids onto the track. Useless in a street car.

In a street car running a plumbed back system, you need an "oil/air separator" which is kind of like a catch can but has strategic baffling to scrub the oil vapour from the air before it is returned to the intake stream.

You can run a "catch can" AND an "oil/air separator" and then plumb back to the intake. For a stock street car this is overkill, only a separator is needed to scrub those nasty oil vapours out. For a modded street car with bigger turbo, making reasonable power and gets beaten up on then the catch can and separator setup would be beneficial while remaining legal.

If you block the PCV valve then must also block the return to the intake pipe. Basically, vent cam covers to catch can and then vent to atmosphere (those little filters you see on top of catch cans). I also vent my dipstick to the catch can to help reduce oil stuck in the head.

[Tony de Wonderful]

Did you leave it plumbed to the intake?

If you block the PCV valve you HAVE to run atmo..

Is that so? I've see a few set ups with the PCV blocked but the two ports on the rocker covers routed back to the intake either by way of a catch can or not? What's the problem with taht?

[rob82]

Is that so? I've see a few set ups with the PCV blocked but the two ports on the rocker covers routed back to the intake either by way of a catch can or not? What's the problem with taht?

Your AFM wont be metering the air that is drawn in through the catch can vent - leaning the engine out.

[JonnoHR31]

obviously you dont run to the intake and vent the can to atmo. he means a sealed system with the pcv blocked but the intake hose still in place

[W0rp3D]

Back to what i believe was part of the original question and what i would like to know, is it better to use bigger breather hoses to get more out faster than standard, i have mine plumbed up in the factory configuration but i use a line from the cam cover that does not have a restrictor in it like the factory line does, it then runs through a catch can filled with stainless steel wool as a filter and then back to the intake pipe, is this better/worse/no different to have the restrictor in the line?

[Birth]

Hi guys, im looking for opinions as to why the catch can helped blow my from seal and what I need to change to get the system to work. Thanks Ben