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

[snwtoy]

It's true..

It looks like it vents into the top of the airbox. But take the top of the airbox off and have a closer look - there's a sealed chamber built into it that the bov is 'venting' into.

Now this begs the question.. how the hell does a bov work if it's vent is blocked? - answer? It doesn't work. Which would account for the fact it is dead silent in standard form.

Doesn't make sense to me.. did the designers know what it was supposed to be doing?

Fivebob - any insights?

[CozmoNz]

maybe the bov side of things is fine.

the *airbox designers* are a bit retarded?

Simple, chuck a wee poddie filter thing on the end of the hose where the bov vents to...

whamo..

or are caldina's afm?

[fivebob]

It's true..

It looks like it vents into the top of the airbox. But take the top of the airbox off and have a closer look - there's a sealed chamber built into it that the bov is 'venting' into.

No it's not true !!8O

If you look a bit closer at the airbox you will find that it is not sealed at all. The chamber vents into the airbox and also supplies air for the idle speed control.

It doesn't work. Which would account for the fact it is dead silent in standard form.

Au Contraire, by the looks I'd say it works very well, but you're right about it being quiet, not sure if they meant it to be quiet or if that's just a by-product of the design.

the *airbox designers* are a bit retarded?

Err no, in fact looking at the design of the airbox I'd say they're actually very smart cookies, I was quite impressed with the way it was put together.

[Crimson Tears]

I'm sure the Toyota corporation whom have been making vehicles sucessfully for years are retarded and don't know how to build induction systems.

[Santa'sBoostinSleigh]

am i right in saying this is a plumb-back design?

i noticed that it was all sealed and bizzo while i was tu-tuing ages ago
i found that if ya remove the pipe from the other end it runs not the best, and if you block the return line it kills the car...

[fivebob]

am i right in saying this is a plumb-back design?

Yes, as are almost all factory BOV's

i noticed that it was all sealed and bizzo while i was tu-tuing ages ago

But it's not sealed, far from it. Just looks sealed until you engage brain and figure out how it really works

i found that if ya remove the pipe from the other end it runs not the best, and if you block the return line it kills the car...

Of course it's run like $hit when you create the boost leak from hell by removing the pipe.

The "return line" as you call it is in fact the air supply for the idle speed control valve, so it's no wonder the engine died

[TygerTung]

All factory blow off valves are there to reduce noise

[snwtoy]

It's true..

It looks like it vents into the top of the airbox. But take the top of the airbox off and have a closer look - there's a sealed chamber built into it that the bov is 'venting' into.

No it's not true !!8O

If you look a bit closer at the airbox you will find that it is not sealed at all. The chamber vents into the airbox and also supplies air for the idle speed control.

It doesn't work. Which would account for the fact it is dead silent in standard form.

Au Contraire, by the looks I'd say it works very well, but you're right about it being quiet, not sure if they meant it to be quiet or if that's just a by-product of the design.

My bad.. I didn't look close enough, I just assumed because it didn't feed into the main intake it went nowhere
Odd that they've incorporated it into the airbox.

Does the idle bypass actually need a rush of air from the bov when you back off the accelerator? I disconnected the bov from the airbox and put a filter over the hole in the airbox.
Car still seems to run fine, but my boost guage isn't hooked up yet so I can't tell if it's leaking boost. Why would it leak boost when disconnected? Out through the idle bypass? Surely that would have a one-way valve somewhere? Or not given it didn't need it when connected to the arse end of the bov? The idle bypass hose isn't attatched with any clips so I assume it's not under pressure

[fivebob]

My bad.. I didn't look close enough, I just assumed because it didn't feed into the main intake it went nowhere
Odd that they've incorporated it into the airbox.

But it does feed back into the main intake, it's just not obvious when you look at it.

Does the idle bypass actually need a rush of air from the bov when you back off the accelerator?

No, not really, but like I said before it doesn't just feed the ISC, it's cleverly feed back into the main airbox in such a manner as to A) not disturb the flow too much, and B) slowly dissapate the pressure.

I disconnected the bov from the airbox and put a filter over the hole in the airbox.

Take my advice and either put it back immediately before you do any damage to the engine from sucking unfiltered air through the bypass, or, if you really must have the Psssst noise, replace it with an aftermarket BOV.

Car still seems to run fine, but my boost guage isn't hooked up yet so I can't tell if it's leaking boost. Why would it leak boost when disconnected? Out through the idle bypass? Surely that would have a one-way valve somewhere? Or not given it didn't need it when connected to the arse end of the bov? The idle bypass hose isn't attatched with any clips so I assume it's not under pressure

It will leak out the vent of the BOV/Bypass valve, the stock valve is designed to use the vaccum of the intake to help it seal when under boost. It also acts as a turbo bypass when off boost by sucking air back through the valve. You must not run it vented to atmosphere or you will suck unfiltered air into you engine, leak boost and ruin the seat of the valve by trapping grit on the sealing surfaces

[RomanV]

or you will suck unfiltered air into you engine, leak boost and ruin the seat of the valve by trapping grit on the sealing surfaces

Speaking from experience there?

[fivebob]

or you will suck unfiltered air into you engine, leak boost and ruin the seat of the valve by trapping grit on the sealing surfaces

Speaking from experience there?

Yeah, other peoples

Actually when you know how the Toyota valve works it just simple logic as to what will happen if you vent it to atmosphere, and it's not nice

[vvega]

see you give good advice and nowone belives you
tell them you have a800 hp ct26 and they all wanna by one

somthimes helping people is just a rod for your own back

v

[Lanius]

see you give good advice and nowone belives you
tell them you have a800 hp ct26 and they all wanna by one

somthimes helping people is just a rod for your own back

v

Try not to get tar over all of us with that brush dude ...

[vvega]

wasent directed just a general statement


v

[snwtoy]

*insert good technical details that make snwtoy look like silly 16 yo idiot*

I will re-examine the airbox tomorrow Hope I haven't done any damage

[snwtoy]

Ok, after my re-examination of the top of the airbox:

But it does feed back into the main intake, it's just not obvious when you look at it.

It doesn't.

No, not really, but like I said before it doesn't just feed the ISC, it's cleverly feed back into the main airbox in such a manner as to A) not disturb the flow too much, and B) slowly dissapate the pressure.

Again, it doesn't feed back into the intake/airbox at all. I can provide pictorial evidence if necessary.

Take my advice and either put it back immediately before you do any damage to the engine from sucking unfiltered air through the bypass, or, if you really must have the Psssst noise, replace it with an aftermarket BOV.

As mentioned, I filtered the bypass line.

It will leak out the vent of the BOV/Bypass valve, the stock valve is designed to use the vaccum of the intake to help it seal when under boost. You must not run it vented to atmosphere or you will suck unfiltered air into you engine, leak boost and ruin the seat of the valve by trapping grit on the sealing surfaces

You're wrong here. As there is no connection between the BOV outlet and the intake, it does not use any intake vacuum whatsoever. Nice theory though.
There is always a higher pressure behind the bov, than at it's outlet, so it will never 'suck' air and grit in anywhere.
The throttle bypass is either a one-way valve, or it is closed when the throttle is opened, so air (boost) cannot leak out through there.

It also acts as a turbo bypass when off boost by sucking air back through the valve.

This part is correct, but all I have effectively done is change the source of the air for the throttle bypass, from air from the bov just in front of the throttle, to ordinary filtered air. I can't see this causing trouble, and the engine doesn't seem to mind at all, so long as there is air to suck.


Thoughts?

[Wildcard]

Regarding the stock BOV sucking air and leaking - I have read for a long time similar ideas to what Fivebob is saying, that the valve acts as a bypass at part throttle and will indeed leak without the intake connection.

However, my own basic tests show otherwise... [this is with an MR2 factory BOV]:

I ran a tube from the BOV outlet to the cabin to test if the BOV was leaking in this arrangement, the answer was no, held 16psi without fail and there was no noticeable vacuum from the tube anywhere in the throttle range. The only time the valve opened [this was extremely audible] was when the throttle snaps shut.

I run mine vented to atmosphere at the moment because of a piping problem rather than a desire for more noise. I still run mine with a filter also - just to be safe.

[Mr Revhead]

arnt the sw20 and st215 ones different?
the sw20 one being twin chamber, as in one vacuum chamber to open, and another on the other side to close it?
and the st215 being single? one to open only? and a spring/intake vacuum (through air outlet) to shut it? thats my understanding. having said that im going to go look at my mates one to confirm my memory.

also its not at all uncommon for BOV to suck a little as they shut, especially the loud ones, as they use a softer shut off to make more noise, and for a fraction of a second they are still closeing while the intake is sucking.... at least thats what a lot of the older ones used to do.

snwtoy: the air bypass valve (BOV) mounts so it vents into the top of the airbox, if it doesnt feed back into there where does it vent to?

[snwtoy]

snwtoy: the air bypass valve (BOV) mounts so it vents into the top of the airbox, if it doesnt feed back into there where does it vent to?

That's been my point all along.. it doesn't vent anywhere except to the throttle bypass line. In other words it's not really as efficient as it might be in factory form as the bypass line is long and quite small in diameter.

Is there proof that there is suction in the section between turbo and throttle? I would like to think that with the bov allowing the turbo to stay spooling there is always positive pressure behind the throttle? Even if this is not the case, the suction must be almost insignificant as many aftermarket bov's don't bother to filter the air sucked back through?

Here's my simple diagram of the GT-T intake - note that until you actually take the lid off the airbox and examine it closely you would assume the bov vents back to the intake.

*edit - misleading pic removed

[fivebob]

Ok, after my re-examination of the top of the airbox:

But it does feed back into the main intake, it's just not obvious when you look at it.

It doesn't.

Then you didn't perform any tests other than a visual examination, did you?

No, not really, but like I said before it doesn't just feed the ISC, it's cleverly feed back into the main airbox in such a manner as to A) not disturb the flow too much, and B) slowly dissapate the pressure.

Again, it doesn't feed back into the intake/airbox at all. I can provide pictorial evidence if necessary.

Pics will show nothing, you need to examine in another manner

As mentioned, I filtered the bypass line.

No, from your description you filtered the Idle speed control, not the Turbo bypass/bov.

It will leak out the vent of the BOV/Bypass valve, the stock valve is designed to use the vaccum of the intake to help it seal when under boost. You must not run it vented to atmosphere or you will suck unfiltered air into you engine, leak boost and ruin the seat of the valve by trapping grit on the sealing surfaces

You're wrong here. As there is no connection between the BOV outlet and the intake, it does not use any intake vacuum whatsoever. Nice theory though.

Sorry but I'm not wrong, it's you that doesn't understand the bypass function of the valve not me.

It's not theory, it's fact. The Bypass valve sucks air when off boost, it's been proven many times not just by me. I have observed many times in my current car by by the strange whistling noises it makes on partial throttle.

There is always a higher pressure behind the bov, than at it's outlet, so it will never 'suck' air and grit in anywhere.
The throttle bypass is either a one-way valve, or it is closed when the throttle is opened, so air (boost) cannot leak out through there.

Hate to say it again, but you're wrong. The valve has low pressure behind it when there is high airflow, through the depression in the airbox, which it is connected to!!!!.

It is a bypass valve for off boost, it does suck air through when there is no boost in the manifold to keep it closed.

It also acts as a turbo bypass when off boost by sucking air back through the valve.

This part is correct, but all I have effectively done is change the source of the air for the throttle bypass, from air from the bov just in front of the throttle, to ordinary filtered air. I can't see this causing trouble, and the engine doesn't seem to mind at all, so long as there is air to suck.

I suspect what you call the "throttle bypass" is the idle speed control valve. The bypass function I referred to is different, it works at all throttle openings when off boost and does not bypass the throttle plate.

Thoughts?

I think you need to learn to examine and test things in an other than visual manner. Perhaps you'd like another cahnce to redeem yourself and post the corrections before I provide proof that what I say is correct?