Krankvent Conundrum

[AC]

Now would anybody think that KV's need to be accounted for in the mapping process???

[frogger]

I assume your talking about a brand name PCV (Positive Crankcase Ventilation) valve?

As I figure it your crankcase is either properly vented, or it's not (as far as mapping is concerned).

If it's properly vented - carry on mapping.
If it's not then you might end up tuning 'around' the issues the blocked PCV is causing (such as high or lumpy idle for instance).

I don't claim to be an expert on this issue though by any means!

Why do you ask? Custom crankcase venting?

[markiii]

crankvents, nope

[AC]

Car is already mapped being FI, but the KV's weren't fitted at the time. Just the standard PCV was present and did/does function fine (presumably).  I've added KV's since as most turbo peeps believe they are a worthwhile safety step as in some cases the standard PCV can be overcome by boost and the crankcase then gets pressurised which prevents the turbo oil feed return from draining back into the sump, the pressure build then can force oil out around the turbo shaft seals and into the inlet, cooler matrix, TB, showing oil burning signs etc.

I don't believe my Apexi actually suffers from this problem........  (yeah I know if ain't broke and all that).

Anyway when I put the KV's on I notice a drop in performance, vibration under full throttle and on one occasion the AFR dropped to 10 on full throttle.

All in all I am thinking 'yes' to my original question, just seems unlikely. Take them off, seems back to before  s:?: :?: s:?:  .

[markiii]

did you put them in the right way round?

[frogger]

Boost leak following fitting of krankvents?
Either through an actual leak, a knackered krankvent allowing boosted air to go into the crankcase, or a krankvent fitted wrong way round?

AFR ratio points towards that sort of thing.

Unplug crankvent end furthest away from engine and blow down it - you shouldn't be able too. suck on it and you should get a bit of oil and air  s:lol: :lol: s:lol:

EDIT: Damn, markiii beat me to it

[AC]

Fitting direction was my thought and yes I have been sucking and blowing them  s:lol: :lol: s:lol:  .

The first KV sits next to the standard pcv on the line from the TB. It's direction should allow scavenging of cc gases when the throttle is shut and the line to the std pcv is in vacuum, this same line when throttle is open and under boost should stop any cc pressurisation as the KV flow direction is pointing away from the std pcv back to the TB.

The second KV sits on the breather line from the back left of the cam cover that joins the intake pre turbo post filter and MAF.  This one flows away from the engine so when the throttle is open and the turbo is sucking it will draw air mainly through the intake but also allowing this breather line to scavenge of any cc gases.  In this direction it should also prevent any air being drawn back into the cc when the throttle is shut and vacuum is drawing on the above other line.

Does that sound right?

[frogger]

The cc vent system needs to draw in fresh air from one end (the breather) and expell any blow-by contaminated air from tother end (pcv valve) - If I've interpreted the system described in your last post correctly, then there's no 'fresh air' feed due to the direction of both valves only allowing air out of the case.

The vast majority of my experience is with non-turbo engines, so I can't comment on the 'best' way to vent the cc with a turbo.
However, it's pressure differenentials that matter, not just the pressure of the inlet air.

I would definately check with a more experienced turbo-engine builder on this, rather than just take my word, but I would think that the intake manifold's air pressure will still be less than the crankcase air pressure even on a turbo engine (though the individual bar/psi pressure values will no doubt be much higher) and as such the pressure differential to scavenge blow by gas should still exist. No harm in having a 'stronger' krankvent branded PCV to resist the higher pressures in the system on the occasions where the differential doesn't exist, but I'd question whether the whole system needs rerouting due to turbo'ing, and would also question whether a one way valve of any kind is required on the breather (though a catch can rather than a direct to inlet system is always a nice addition).

[frogger]

The following link has a 'stock' Toyota PCV diagram on page 2, note the two-way flow of the breather hose...

 m http://www.autoshop101.com/forms/h63.pdf m

[muffdan]

My understanding of the krank vents is to stop the boosted side of inlet manifold from putting pressure into the crank case. Doing so would cause that pressure to push air and oil out the other breather pipe and depending on what that pipe does, it will blow oil all over your engine bay or back into the inlet and through the combustion chamber. Not good.

So, you want the vent between the TB and rocker cover gasket to allow air to flow from the CC to the inlet. This stops the CC from seeing boost.
You then want the other vent to allow air to pass from atmosphere (or better still from the inlet pre-turbo like on the TTET setup) into the breather.

Someone please correct me if I'm wrong  s:) s:)

[frogger]

Wouldn't this do the job?
As said, I'm not used to turbo engines, just trying to get it straight in my own head.



Excuse the pic quality   s:lol: :lol: s:lol:

[VVT-i]

My KV setup is as follows...

Small Krankvent

I have mine placed inline between the PCV and inlet manifold, I also have a catch tank in this line to..

PCV - Catchtank - Krankvent - Inlet Manifold

The the Krankvent here prevents boost pressure from the inlet manifold entering the crank case, the PCV has the hoses to the catch tank, the catch tank itself and the hose to the Krankvent in wich to work as designed, the catch tank catches any oil vapour drops helping to keep things that little bit cleaner.. the arrow on the Krankvent pints away from the engine.

Large Krankvent

I have this "inline" between the crank case breather and the throttle body, under boost the Krankvent prevents boost pressure entering the engine, under normal conditions the brether works as normal venting back into the throttle body.

Some people choose to vent this Krankvent to atmosphere and fit a small filter onto the Krankvent, they then plug the hose by fitting a bung on the hose coming from the throttle body to prevent a vac leak. IMO this can lead to a dirty engine bay, I also feel there is no need to vent to atmosphere at all as you are only on boost a very short time before the breather vents as normal.

I have ran with this setup for around 3 years with no problems to speak of.

[markiii]

krankvents are designed to generate vaccuum in teh crnakcase

they should allow air out of teh crankcase but not air in.

fitted any other way you might as well not buy them


small crankvent should go in teh pcv line allowing air from teh crankacase out

large crankvent should go in teh rear breather line, and allow air out of teh crankcase

[markiii]

that said, on your Apexi I seem to remember that teh rear breather goes to the Apexi intake pipe, pre turbo, and teh TB connection now has a bung, correct?

[AC]

You're right Mark, the TB outlet is bunged!  So if I've got a KV sat on the line that connects to the standard pcv does that mean I'm wrongly plumbed?  The other end of that line disappears to another line which I thought was connected to the TB  s:oops: :oops: s:oops:  . I'm now wondering where or even if a KV to prevent boost entering the crankcase works/is needed on my Apexi?

[markiii]

the standard pcv line goes to teh intakemanifold so having a correctly plimbed KV in that line is a benefit.

so concentrating on teh rear breather, am I right in saying it goes from teh breather on teh back of teh cc into a crankvent and then from there to teh pre turbo but post air filter intake pipe?

remind me where the MAF currently sits?

[AC]

the standard pcv line goes to the intakemanifold so having a correctly plimbed KV in that line is a benefit.

The KV fitted in that line only allows air flow out of the engine, is that right?

so concentrating on the rear breather, am I right in saying it goes from the breather on the back of the cc into a crankvent and then from there to the pre turbo but post air filter intake pipe?

Correct, seen in the photo here as the thin blue silicon pipe running under the brace next to the barrel.

remind me where the MAF currently sits?

It sits immediately behind the cone filter, out of shot in the bottom left, about as far forward in the intake as possible.  The breather line mentioned above connects back to the intake (where Apexi is written) pre turbo and is about half way between MAF and compressor wheel.

[VVT-i]

the standard pcv line goes to the intakemanifold so having a correctly plimbed KV in that line is a benefit.

The KV fitted in that line only allows air flow out of the engine, is that right?

Correct, both KVs only allow air to get out of the crank case.

When an engine runs it creates it's own pressure (piston movement) this pressure must be vented out of the crank case, through the pcv into the inlet manifold (small KV here.. flowing away from the engine) and via the top breather into the TB (standard setup of course) large KV here.

Cut the hose between the PCV and inlet manifold and fit the small KV as near to the inlet manifold as you can get it,

As for the large KV.. I'm not familiar with your set up, someone who knows how your Apexi is plumbed in would be better to advise on that one... but we're half way there lol.