Oil catch can/ Breather

[MWP]

Agreed though, that a CORRECT oil catch can (or oil/air separator) system should take the PCV gases from the crankcase, route them into an oil/air separator (aka catch can), and then have the gases pass back into the intake of the engine before the throttle butterfly.

Incorrect.
The gasses need to be sucked out of the crank case, hence why it goes to the inlet manifold after the TB.

I dont get what you mean by this extra pipe though...

If you just suck air from the crank case, itll create a vaccum... but the bad gasses will still be in there.
By having a small breather pipe from before the TB to the crankcase, clean air can get in so the dirty air can all be sucked out.

Nearly every factory engine is setup this way.
Some are more elaborate than others with solenoids to control when the air flows, etc, but they all work the same way in principal.
Allow clean air in, pull the dirty air out.

[The Witzl]

But what about on a turbo-charged engine? Would you still have the crankcase vent after the TB, with a secondary vent before the TB?

How about on a 4A-GE where there is only one crankcase vent which is connected directly in front of the TB as i mentioned earlier?



What you have stated makes sense for an old carburetted engine like the 2T-G or 18R-G that has the two vents (and in fact thats how its done on the 18RG from factory, now that i think about it)..
... but you do realise that in effect what you are doing is allowing air to BYPASS the TB, thus increasing idle - if this is not the PCV system config from factory.

[takai]

Nor does it work particularly well for ITBs. But that aside the crankcase is under pressure anyway, you dont need to suck the oil vapour out, it has a positive displacement pressure anyway.

[MWP]

But what about on a turbo-charged engine? Would you still have the crankcase vent after the TB, with a secondary vent before the TB?

Yes you could.
The positive pressure wouldnt go back into the crankcase due to the PCV valve.

What you have stated makes sense for an old carburetted engine like the 2T-G or 18R-G that has the two vents (and in fact thats how its done on the 18RG from factory, now that i think about it)..
... but you do realise that in effect what you are doing is allowing air to BYPASS the TB, thus increasing idle - if this is not the PCV system config from factory.

Thats where the PCV valve comes in.
It only opens when there is enough of a vaccum from the inlet manifold, like when cruising or downshifting.

Nor does it work particularly well for ITBs. But that aside the crankcase is under pressure anyway, you dont need to suck the oil vapour out, it has a positive displacement pressure anyway.

It can still work with ITB's, in the same way brake boosters still work.

The crank case should be at a slight vaccum though... i listed the advantages of this earlier.

Companies do actually make pumps that vaccum air out of the crankcase maintaining a constant negative pressure.
It has been shown to increase engine power due to better pistion ring sealing reducing blow-by.

[Biggo]

Yes you could.

Companies do actually make pumps that vaccum air out of the crankcase maintaining a constant negative pressure.
It has been shown to increase engine power due to better pistion ring sealing reducing blow-by.

This sounds interesting, do have any idea where i can start looking into it? A brand or something.

[MWP]

This sounds interesting, do have any idea where i can start looking into it? A brand or something.

A bit of info here:
http://www.dragstuff.com/techarticles/vacuum-pumps.html

Lost more:
http://www.google.com.au/search?q=crankcase+vacuum+pump

[The Witzl]

I wouldnt trust a PCV valve to hold against 15psi + from a turbocharger..... especially at something like 6000rpm!!

I have priced up some aftermarket PCV valves that are designed to withstand that sort of pressure - and at $80+ i decided that just using the intake pipe before the turbo was a better idea

Dont get me wrong MWP, i'm not arguing with you or trying to discredit you, i'm only trying to draw out the most information from this discussion as possible..... and help me get the most understanding and knowledge in this area as possible

[4agte]

the gt autosound drag s15 uses one aparantly and im pretty sure they are pushing more than 15psi dont know what brand tho

[MWP]

I wouldnt trust a PCV valve to hold against 15psi + from a turbocharger..... especially at something like 6000rpm!!

I have priced up some aftermarket PCV valves that are designed to withstand that sort of pressure - and at $80+ i decided that just using the intake pipe before the turbo was a better idea

15psi really isnt a lot.
I think i would try a standard one first just too see what happens.
The stock PCV valves ive come across look like thay would hold ok.
They might leak a tiny bit, but that wont effect anything.

Dont get me wrong MWP, i'm not arguing with you or trying to discredit you, i'm only trying to draw out the most information from this discussion as possible..... and help me get the most understanding and knowledge in this area as possible

No problem... we would all be clueless if these little debates didnt take place

[mic*]

Tap your PCV line as close to the source of blowby gases as possible.

Install one can (any sealed can/bottle) that has a line running in (blowby source) preferably that extends a few cm's down from the can/bottle top, and i line running out straight from the top.

The reason CAMS reccommends a size based on displacement is coz thats what will determine blowby volume.

Essentially the larger the better coz the gas velocity will slow more and more oil will condense.

Its a bloody simple concept. You must plumb it back on late model cars to meet emmissions regulations. For toyota PCV systems check this out: http://www.autoshop101.com/forms/h63.pdf

[The Witzl]

its not the pressure that i see as being the problem - its the force exerted upon the PCV that i see as the problem..... when you have the engine at 6000rpm +15psi boost, thats a SHITELOAD of air being rammed into the engine, and subsequently a pooload of force from that air.

If it leaked - then HELLO Mr pressurised crankcase. Something I DONT want in an 18R-G!!

[mic*]

its not the pressure that i see as being the problem - its the force exerted upon the PCV that i see as the problem..... when you have the engine at 6000rpm +15psi boost, thats a SHITELOAD of air being rammed into the engine, and subsequently a pooload of force from that air.

If it leaked - then HELLO Mr pressurised crankcase. Something I DONT want in an 18R-G!!

Karl, pressure is pressure mate. With no flow, ie blocked, its doesnt matter how much potential flow there is untill it breaks - from too much pressure.

[mic*]

Look at it this way, a compressor for air tools will obliterate the valve - far too much pressure for the valve, but when it does, it will only flow the small flow rate that it can acheive.

You could have something flowing like Niagara but if it dont have enough pressure, it just doesnt have enough force to break things.

Pressure = force per unit area
Flow = volume per unit time

[MWP]

its not the pressure that i see as being the problem - its the force exerted upon the PCV that i see as the problem..... when you have the engine at 6000rpm +15psi boost, thats a SHITELOAD of air being rammed into the engine, and subsequently a pooload of force from that air.

Oh.
You would have the fresh air in not from before the TB like in NA, but before the turbo.
On boost the line after the TB to the crankcase would be blocked by the PCV valve.
Hence the crankcase would never be pressurised.

[Toycrash]

On a racecar DO NOT vent anything back in to intake manifold!
Hoses from block and valvecover to can and drain back to oilpan. But the drain is not supossed to drain everything back, just precaution if can is trying to overfill.
And breather to atmo.

I will not take apart to any legality or class rules, its your job to think where to obey them or not.