Is My Knowledge Of The Pcv Correct?

[zoomzoom]

After cleaning my intake of oily sludge, I installed a catch can filter and my setup is as follows:

The exhaust side rocker cover pipe goes into the catch can, then the catch can feeds back into the pre-turbo inlet pipe.

The rocker cover to intake manifold pipe is now blocked.

Am I correct in thinking when pressure is created in the rocker cover it will flow through out the rocker cover, into the catch can, and back into the intake?

On futher thinking, on a stock setup does gas flow both ways through the turbo inlet PCV pipe? If the manifold is under vacuum then does it draw air through the turbo inlet, through the rocker cover then into the manifold?

I just want to check if there is any problems with my setup.

[bubba]

You only block the PCV valve if venting to atmosphere.

[zoomzoom]

You only block the PCV valve if venting to atmosphere.

I dont understand sorry.

Ill elaborate: If I leave the rocker cover to manifold pipe on, then my oil catch can on the exhaust side seems useless since the manifold will be sucking in oil mist under vacuum?

[bubba]

I dont understand sorry.

Ill elaborate: If I leave the rocker cover to manifold pipe on, then my oil catch can on the exhaust side seems useless since the manifold will be sucking in oil mist under vacuum?

By blocking the pipe from cam cover to plenum, you have effectively block the PCV valve. You only do this if you are running your catch can venting to atmosphere (i.e. NOT returning to the intake).

The PCV valve is designed to suck air from the cam cover when the engine is under vacuum to relieve any pressure accumulated in the crankcase while on boost (that's why it is called a Positive Crankcase Ventilation valve).

The two main way of hooking up a "catch can" are:

1) run both cam cover breathers to "catch can" then "catch can" to intake pipe, leave PCV connected

2) block PCV, run both cam cover breathers to "catch can" then vent to atmosphere via a small filter on the can (this is illegal but prevents any oil mist getting in to the engine)

Really, in option 1 you should be running an "oil/air separator" as opposed to just a "catch can".. a separator is baffled and filled with a medium (such as steel wool) to aid the separation of oil and air so that the air that is returned to the intake doesn't contain oil.

Edited October 5, 2010 by bubba

[simpletool]

The PCV valve is designed to suck air from the cam cover when the engine is under vacuum to relieve any pressure accumulated in the crankcase while on boost (that's why it is called a Positive Crankcase Ventilation valve).

Well yes and no. The PCV is mostly there to vent crankcase pressure during the over-run. ie. when you come off the throttle at high revs. The exhaust side into the turbo inlet works well when the turbo is on boost and therefore the area before the turbo inlet is negative pressure compared to ...well pretty much everything.

When the throttle is shut then this low pressure area is no longer low pressure. Hence the PCV valve opens when the intake manifold is lower pressure than in the cam covers - which is when the throttle is shut (or partially open).

Currently your car is only venting pressure from the cam covers when on boost - this is OK but not ideal. Think of all that time spend under vacuum when the PCV valve would be open.

Edited October 5, 2010 by simpletool

[zoomzoom]

Really, in option 1 you should be running an "oil/air separator" as opposed to just a "catch can".. a separator is baffled and filled with a medium (such as steel wool) to aid the separation of oil and air so that the air that is returned to the intake doesn't contain oil.

Yes thats exactly what I made.

Well yes and no. The PCV is mostly there to vent crankcase pressure during the over-run. ie. when you come off the throttle at high revs. The exhaust side into the turbo inlet works well when the turbo is on boost and therefore the area before the turbo inlet is negative pressure compared to ...well pretty much everything.

When the throttle is shut then this low pressure area is no longer low pressure. Hence the PCV valve opens when the intake manifold is lower pressure than in the cam covers - which is when the throttle is shut (or partially open).

Currently your car is only venting pressure from the cam covers when on boost - this is OK but not ideal. Think of all that time spend under vacuum when the PCV valve would be open.

Ok now everything makes much more sense.

So ideally I will have to make another filter/catch can for the PCV hose.

Edited October 5, 2010 by zoomzoom

[lachlanw]

is it law to have a working pcv in oz ? if so block it . so it looks stock .

if not throw it away and get 2 bungs that fit

[JonnoHR31]

Currently your car is only venting pressure from the cam covers when on boost - this is OK but not ideal. Think of all that time spend under vacuum when the PCV valve would be open.

no its venting all the time through the catch can and intake pipe. the only time the intake pipe isnt sucking air is when the engine is off

[mattymagoo22]

is it law to have a working pcv in oz ? if so block it . so it looks stock .

if not throw it away and get 2 bungs that fit

If you do this and your crankcase has no way of venting pressure the oil will be pushed past the oil seals and it will make quite a mess.

[JonnoHR31]

not if you still have the exhaust side plumbed up

[blind_elk]

then my oil catch can on the exhaust side seems useless since the manifold will be sucking in oil mist under vacuum?

There's nothing wrong with that. The major problem is when you are on boost, and you feed oil mist from the rocker covers to the intake side of the turbo, then into the cylinders. Oil in the air/fuel mix significantly lowers the effective octane rating of the mix, and thus you risk detonation. When the engine is under vacuum, ie off boost, the effect of any oil vapour, entering via the PCV valve, on the effective octane rating is minimal, and thus the risk of detonation is extremely small.

lachlanw, yes in Oz it is a requirement to have a working PCV system, same as it is a requirement to have a catalytic converter, and all the other anti-pollution equipment.

[bubba]

I don't think it's a case of having a "working PCV system" as that is more the manufacturer designing something in to control something else in the engine (i.e. a valve to control the pressurising of the crankcase). I believe it's illegal due to the fact that whatever goes in the intake, has to come out through the catalytic converter. Nothing can be vented before then so you can't run your breather system venting to atmosphere, just like you can't run your bov venting to atmosphere. That's also the reason that screamer pipes are illegal, but you could make one legal if you mounted a small cat converter to it and muffled it to keep it below the accepted noise level.

Note: can't can be read as shouldn't

Edited October 6, 2010 by bubba

[lachlanw]

run a air/ oil seperator in the line between the cam covers and the turbo air pipe . block pcv . end of storey

maggtymagoo your a tard . the line fromt he cam covers to the turbo intake will flow more than ebough to not have any pressur ein the engine . and its always under partial vacuum .

do you want oil in your intake manifold and higher knock values ? no . so f**k the pcv

[zoomzoom]

There's nothing wrong with that. The major problem is when you are on boost, and you feed oil mist from the rocker covers to the intake side of the turbo, then into the cylinders. Oil in the air/fuel mix significantly lowers the effective octane rating of the mix, and thus you risk detonation. When the engine is under vacuum, ie off boost, the effect of any oil vapour, entering via the PCV valve, on the effective octane rating is minimal, and thus the risk of detonation is extremely small.

lachlanw, yes in Oz it is a requirement to have a working PCV system, same as it is a requirement to have a catalytic converter, and all the other anti-pollution equipment.

Just to bump this again, is the rocker cover to turbo inlet vent pipe enough to relieve pressure? If so then why would nissan even bother to fit the rocker cover to manifold pipe? Does it significantly lower the pressure in the engine to stop oil being pulled into the cylinders when under light load?

I ask only because my idle wavers with the RC to manifold pipe functioning, whereas the idle is perfect with the pipe blocked. I put a 3mm restrictor in the pipe to reduce the amount of air the manifold is pulling in under vacuum. It did help, but it seems easier now just to get rid of the whole pipe.

Alas, nissan is full of engineers and I am not, so I am hestitant to block it.

Edited October 17, 2010 by zoomzoom

[gotRICE?]

I had mine blocked for a while, but after a few months it was beginning to smoke a bit out the exhaust. I think just venting straight to atmo, in my application wasnt enough. As i had the Exhaust cam cover to turbo pipe blocked also.