GT-T bov vents to small sealed chamber... wtf?

[snwtoy]

fivebob, I'm quite prepared to eat humble pie, I don't mind learning something new, ever.

Please explain to me the test I should perform to prove that there is a connection between the bov outlet chamber, and the rest of the airbox.

To date I have performed:
Visual test
Touch/feel test
Fluid leak test

Each of these tests have given no indication whatsoever of a connection between the two chambers.

The only outlet to the chamber into which the BOV vents is to the throttle bypass/speed control/whatever that line is called as per my diagram above.
If there is some other semi-permeable membrane involved which will pass air but not fluid, then that is the only other possibility I have not considered.

[fivebob]

fivebob, I'm quite prepared to eat humble pie, I don't mind learning something new, ever.

Please explain to me the test I should perform to prove that there is a connection between the bov outlet chamber, and the rest of the airbox.

To date I have performed:
Visual test
Touch/feel test
Fluid leak test

Each of these tests have given no indication whatsoever of a connection between the two chambers.

Can't understand why, unless your fluid leak test was unsatisfactory, or the airflow is blocked by dirt, which is exteremly unlikely. I suppose you could have a faulty airbox.

The fluid leak test I performed was to block the idle speed control port off and blow through the BOV connection, result no pressure, only flow, ...hmmm thinks... put's hand in airbox, can feel air, but can't see any holes... thinks again... connects BOV port to tap, blocks idle speed port and turns on water, observes where the water flows into the airbox. Hint the tube from the turbo is not completely moulded into the airbox.

BTW I would recommend doing this test if you're planning on driving soon as it a PITA to get rid of the water

The only outlet to the chamber into which the BOV vents is to the throttle bypass/speed control/whatever that line is called as per my diagram above.
If there is some other semi-permeable membrane involved which will pass air but not fluid, then that is the only other possibility I have not considered.

No there is no semi permeable membrane, the valve is kept open by the manifold depression being greater than the depression in the airbox, and air flows back into the manifold as a result. If the valve is vented to atmosphere it doesn't have than airbox depression and will stay open longer and not close properly, so is prone to leak, it also sucks unfiltered air directly into the engine .

That's why I said you don't understand the Bypass function of the valve, you're assumuing it's the same as an aftermarket BOV, which I repeat it's not!!!.

BTW if you didn't plug the BOV & Idle speed feed in the airbox you are also sucking unfiltered air through those.

FWIW I usually don't post in such definite terms, (with bold and colour) unless I'm very certain of my facts, don't like the taste of humble pie

[snwtoy]

Fivebob - I have just found a rubbery gasket/sealant running around the inside of the joint in the mouldings of the airbox lid
Is it possible that yours doesn't have this seal and as such vents air into the top of the larger chamber?

[fivebob]

Fivebob - I have just found a rubbery gasket/sealant running around the inside of the joint in the mouldings of the airbox lid
Is it possible that yours doesn't have this seal and as such vents air into the top of the larger chamber?

It does not and I have two examples that show this. Neither should yours as the BOV will not function correctly with the chamber sealed.

Perhaps the previous owner put it there. Possibly because they removed the stock BOV, other than that I can see no reason for it unless the they had the brains of a chocolate fish

[fivebob]

Fivebob - I have just found a rubbery gasket/sealant running around the inside of the joint in the mouldings of the airbox lid
Is it possible that yours doesn't have this seal and as such vents air into the top of the larger chamber?

Oops just re-read your post....

Do you mean around the tube going to the turbo, which is where it vents, or around the edge of the lid???

[rodstr]

i found a little hole just behind the arrow

[fivebob]

i found a little hole just behind the arrow

It's not just that little hole either, though that is a visible sign. Air leaks from all around the joint inside of the tube that your arrow is pointing at.

[snwtoy]

I too have found a hole where rodstr has pointed. It's hard to see, but mine was filled with a black rubbery substance. Looks like it wasn't a gasket afterall, I've just spent the last hour picking black rubber from around the tube and that hole.

Now there is definitely a vent = air coming from that hole and around the edge of the pipe to the turbo. Is this how it is supposed to be? I don't want to put mine back on now in case I suck some of this rubbery shit into the motor

Assuming I get rid of the black shit and it doesn't go into the motor, if I disconnect the bov, and filter the hole where the bov is connected is this going to allow unfiltered air into the engine?

[fivebob]

Assuming I get rid of the black sh*t and it doesn't go into the motor, if I disconnect the bov, and filter the hole where the bov is connected is this going to allow unfiltered air into the engine?

Yes it will still suck unfiltered air into the engine, via the bypass function of the BOV. If you disconnect the BOV from the airbox, you have to attach a filter to it. Even then it's still prone to leaking as they are not designed to be vented to atmosphere, if you want to do that then I suggest that you replace the BOV with an aftermarket item.

Guess the PO of your car either had no brains, or ran an aftermarket BOV, or possibly both

[snwtoy]

Well I've got a big thank-you to say to fivebob for helping clueless fools like myself work out this all goes together.

One more clarification though, if I do get a replacement bov, what becomes of the turbo-bypass feed?

[vvega]

good man im sure your gratatude will be greatly aprecialted
it is truly rare to get a thank you here
well done

v

[snwtoy]

I'm getting more and more confused now

Firstly, is this diagram correct?

Secondly, can you name the numbered parts for me?

I have:
1 = idle speed control
2 = bov actuator line
3 = one-way restricted airflow valve which seems to slow the closing of the bov, rather than letting it snap shut.

Also, can someone confirm tha the purple side of the one-way valve is closest to the bov... I took it off and am not sure which way round it goes back..

Damn.. updated again with valve pointing the other way..

[snwtoy]

Can someone describe for me the moment there is enough negative pressure to open the bov for the bypass function fivebob describes? And explain if this is by design why there are no aparent issues with adding an aftermarket valve which will not open under negative pressure?

[fivebob]

Can someone describe for me the moment there is enough negative pressure to open the bov for the bypass function fivebob describes? And explain if this is by design why there are no aparent issues with adding an aftermarket valve which will not open under negative pressure?

Chamber (A)- connected to the manifold
Chamber (B)- connected to the manifold via one way restrictor
Chamber (C)- Turbo pressure
Chamber (D)- the airbox.

(A) & (B) are separated by a diaphragm

Under boost (A) & (B) have the same pressure The valve is kept closed by the spring, plus boost pressure in (C), and the depression in (D).

When the throttle is closed (A) sees vacuum and pulls the valve open, (B) still has pressure and assists in the fast opening of the valve, slowly it reaches the same pressure and the valve closes, pressure fluctuations in (C) & (D) from the venting makes the valve oscillate between open and closed.

When the throttle is partially open and the engine is not Boosting vacuum in (C) causes the valve to lift from it's seat allowing a small amount of air to enter the intake. If the throttle is reduced at this point then (A) sees more vacuum than (B) and the valve opens and is kept open by the depression in (C) when the pressures in (A) & (B) equalise. This is the bypass function I was referring to.

As to whether this is by design or a by-product of the design I don't know, but it would allow for the engine to increase flow at a marginally faster rate when the engine is off boost. However this function is not necessary for the normal operation of the engine which is why aftermarket BOV's don't cause problems.

The design of this valve is superior to most aftermarket valves (especially the cheap ones) in that the more boost the tighter the valve seals, unlike most aftermarket valves that rely on the spring pressure to keep them closed and hence have a slower response.

Looking at this diagram I can't see why they would leak when vented to atmosphere, the assistance provided by the depression in the airbox shouldn't affect the sealing that much. However the anecdotal evidence suggests that they do, perhaps that is just a myth, or possibly caused by grit being trapped on the sealing surface if a filter is not used.

[snwtoy]

Thanks again Fivebob, I like diagrams

I think the "one-way" valve attatched to chamber B needs a little more explanation.
I sat with the bov on my desk for a few hours yesterday, trying to fathom how it works.

It would seem that the 'one way' valve is actually a variable restriction valve - it restricts airflow in both directions, but it restricts a lot more in one direction than the other. Positive pressure toward (B) is restricted more than negative pressure. This means that chamber (B) is happy to go negative and close the valve, but only reluctantly helps to help open the valve.

Under boost, intially (A) will see greater pressure than (B) and close the valve. When the pressure at (A) and (B) equalizes it will be the spring and the pressures at C and D keeping the valve closed.

When the throttle is closed, (A) sees vacuum, and (B) will also see vacuum but because of the valve restriciton it will intially be less than (A). Allowing the valve to open.

As the pressure in the manifold equalizes, (A) equalizes (B) will be slower to equalize, maintaining the pressure imbalance and closing the valve before positive boost pressure arrives.

I think?

[fivebob]

It would seem that the 'one way' valve is actually a variable restriction valve - it restricts airflow in both directions, but it restricts a lot more in one direction than the other. Positive pressure toward (B) is restricted more than negative pressure. This means that chamber (B) is happy to go negative and close the valve, but only reluctantly helps to help open the valve.

I think it's the opposite to what you describe, i.e. it restricts vacuum more than boost, so that it both opens and closes the BOV faster. I'll check when I'm at my workshop this afternoon to make sure.

BTW the offical acronym for this device is a VTV (Vacuum Transmitting Valve) and it's an expensive piece of plastic for it's size as several US MR2 owners have found out when Toyota quoted them $US40 for a new one

[snwtoy]

I think it's the opposite to what you describe, i.e. it restricts vacuum more than boost, so that it both opens and closes the BOV faster. I'll check when I'm at my workshop this afternoon to make sure.
BTW the offical acronym for this device is a VTV (Vacuum Transmitting Valve) and it's an expensive piece of plastic for it's size as several US MR2 owners have found out when Toyota quoted them $US40 for a new one

If that is the case I may have re-installed it backwards.
Can you confirm whether I need the purple side facing the bov, or the black side?

[fivebob]

I think it's the opposite to what you describe, i.e. it restricts vacuum more than boost, so that it both opens and closes the BOV faster. I'll check when I'm at my workshop this afternoon to make sure.
BTW the offical acronym for this device is a VTV (Vacuum Transmitting Valve) and it's an expensive piece of plastic for it's size as several US MR2 owners have found out when Toyota quoted them $US40 for a new one

If that is the case I may have re-installed it backwards.
Can you confirm whether I need the purple side facing the bov, or the black side?

Purple side goes to the BOV.

I've updated the diagram above to show the flow restriction of the VTV. It provides restriction both ways, but is more restrictive to flow from the BOV (i.e. Vacuum in the manifold)

[vvega]

that is a great bit of info there fivebob and the effort you have gone to to help is admerable to say the least

i vote the diagram and explanation gets faq'ed for furture referance as i can see this been a plague later on as they get cheaper and become more comon:S

v

[10k 20v]

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