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magn1t
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All you need to know about factory BOVs

Mon 13 Aug, 2012 11:43 am

First of all, read this.....like most US sites, its not 100% correct
.http://www.stealth316.com/2-bov1.htm

Here's a rough diagram of how the BOV looks inside.
It's better than an aftermarket one because it's designed as a safety valve. It's supposed to open with excess boost, an aftermarket one won't.
It's also open at idle.That's why vent to atmo makes them stall, it's got nothing to do with metering air and dumping it making it go rich, it's because air goes in through the BOV, bypassing the AFM in turn dropping the Hz signal to zero, making it stall.

Image
edit
The pics have gone but there's a link here to another site.
http://www.bimmerforums.com/forum/showt ... hold-boost

There's 4 chambers in it, 2 will try to keep it closed with positive pressure, the other 2 will try to open it with positive pressure.

So, the spring plus pressure in A will hold it closed
Positive pressure in C will hold it closed.
Positive pressure in both B and D will force it open.

Lets say we get the boost up to 13 ish PSI. that's with respect to atmospheric pressure.
In A there's 13 PSI plus the spring.
In C there's zero.
In B there's a bit less than 13 PSI.
In D there's 13 PSI.

A and D are equal and opposite so cancel leaving just the spring.
C is always zero.
That leaves just B, C and the spring.
As the boost rises, so does the pressure in B which eventually overcomes the spring pressure so it vents.
The pressure in B will always be between the pressure in C and D due to leakage/vent hole.

Lifting the throttle, the pressure in A drops and the pressure in B and D overcomes A and the spring, it opens.
Likewise, when the engine is idling, THE VALVE IS ALWAYS OPEN. it's very important.


Reversing it works(C to the Y pipe, D to vent) , so long as you've got 9B or 13G turbos that hold less that 13 or so PSI to the red line.
The spring + boost in A plus boost in C will hold it closed.
Atmo in B and D, it won't leak.

Lifting the throttle, boost at C will still try to hold it closed as will the spring, vac at A has to be sufficient to open it. Again the pressure in B will be between C and D, that determines whether it will open or not. Higher boost = it's harder to open to the point where it won't open at all until the boost drops.

So that's how it is from the factory.

Next step. Modification.

Image

There's the tools needed to mod it easily
Looking back at the diagram, all you need to do is to block the vent hole between B and D (RTV).
Then make a hole in the plastic divider between B and C.(melt it with a hot welding rod)
( Alternatively you could make and external hole so that it looks like the GReddy)
Then it'll be the same as most aftermarket valves with 3 chambers.
B and C will always be at the same pressure so they cancel out.
That leaves just A plus the spring fighting against D.
A and D will always be at the same pressure so long as the throttle is open, they cancel out leaving just the spring to hold it closed.

You can see the tester I made, I got a modded one up to 60 PSI(air compressor and air line) without leakage and the hose blew off.


If you're feeling bored and want some entertainment at the expense of retards, check this out.

http://www.3sgto.org/threads/3007-Open- ... d-Loop-BOV

Steve
Last edited by magn1t on Sat 03 Sep, 2016 8:23 pm, edited 2 times in total.
quote from barryboys.
Yes, yes, yes, that might be so, but you're clearly missing the bigger picture.....
4 intercoolers!!!!!!!!
Beat that!!!!
 
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Scruffy
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Re: All you need to know about factory BOVs

Mon 13 Aug, 2012 9:58 pm

interesting. shouldve just made a video to prove it's open at idle and that pretty much wouldve sorted most of it, seeing as nobody seems willing to go have a look at their own
"GTO's have a turbo?!"
~Mag & Turbo
 
magn1t
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Re: All you need to know about factory BOVs

Thu 01 Sep, 2016 2:30 pm

I mislaid my tester a while back.
Then I found it again with a tidy up but put it in a safe place.
But I found it again.

https://www.youtube.com/watch?v=l9JRbr1Cfuc

Followed by

https://www.youtube.com/watch?v=5SvVUq1zhCA
quote from barryboys.
Yes, yes, yes, that might be so, but you're clearly missing the bigger picture.....
4 intercoolers!!!!!!!!
Beat that!!!!
 
skates
Posts: 47
Joined: Fri 28 Aug, 2015 8:55 pm

Re: All you need to know about factory BOVs

Fri 02 Sep, 2016 11:14 am

Don't look here. You don't want fast. Fast is bad. I do know a guy but you can't tell anyone. Spies everywhere.
Last edited by skates on Mon 21 Nov, 2016 12:43 am, edited 1 time in total.
 
magn1t
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Re: All you need to know about factory BOVs

Fri 02 Sep, 2016 2:26 pm

skates wrote:
You should fit a JDM ecu :D

????????????


Here's another vid. It's the same Evo BOV, just modded now so it doesn't leak.

https://www.youtube.com/watch?v=ddSJkx0 ... e=youtu.be
quote from barryboys.
Yes, yes, yes, that might be so, but you're clearly missing the bigger picture.....
4 intercoolers!!!!!!!!
Beat that!!!!
 
skates
Posts: 47
Joined: Fri 28 Aug, 2015 8:55 pm

Re: All you need to know about factory BOVs

Fri 02 Sep, 2016 3:31 pm

We are pleased to announce less power was made by this experiment.
Last edited by skates on Mon 21 Nov, 2016 12:42 am, edited 1 time in total.
 
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Scruffy
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Re: All you need to know about factory BOVs

Fri 02 Sep, 2016 8:43 pm

I think youve mistakenly thought magn1t was the one complaining about stalling etc in one of his links to a yanky forum.
Not to mention youd be pretty damn hard pressed to find anything but a 'JDM' ecu in NZs GTOs anyway
"GTO's have a turbo?!"
~Mag & Turbo
 
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Scruffy
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Re: All you need to know about factory BOVs

Fri 02 Sep, 2016 8:43 pm

also, nice reply 4 years later steve :lol:
"GTO's have a turbo?!"
~Mag & Turbo
 
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box
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Re: All you need to know about factory BOVs

Fri 02 Sep, 2016 8:56 pm

Shivers, 4 years?.....time flies.
Image
 
magn1t
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Re: All you need to know about factory BOVs

Sat 03 Sep, 2016 12:47 am

yes, time flies.............but what's the rush?
So I'll cobble up the modded evo BOV on the red GTO, vented........take a video of it open at idle? So It keeps stalling.


The black car is all back together but I've flooded it again.........wrong ECU.

But before I do that...........I've still got the dragsport BOV on the red car, the diaphragm split so it was an air leak.
I RTVd it up to get the fuel trims back to 100%.
I'll made a video of that too?
On the pressure tester?

Performance parts?
quote from barryboys.
Yes, yes, yes, that might be so, but you're clearly missing the bigger picture.....
4 intercoolers!!!!!!!!
Beat that!!!!
 
skates
Posts: 47
Joined: Fri 28 Aug, 2015 8:55 pm

Re: All you need to know about factory BOVs

Sat 03 Sep, 2016 5:31 am

Scruffy wrote:
I think youve mistakenly thought magn1t was the one complaining about stalling etc in one of his links to a yanky forum.
Not to mention youd be pretty damn hard pressed to find anything but a 'JDM' ecu in NZs GTOs anyway


Nah, I'm just pointing out Steves reason for the stalling isn't right using a large slab of irony.
 
magn1t
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Re: All you need to know about factory BOVs

Sat 03 Sep, 2016 9:45 am

They stall when the airflow signal drops to zero...............as I'll show with a vid.
Maybe in another 4 years time.
Air flows IN through the open BOV.
Air also flows OUT through the open BOV depending on the conditions at the time.The speed of the turbos.
Which.......you guessed it......they don't spin when the engine is idling properly.


The ECU will ignore the AFM reading when the throttle switch is closed.Only when it's closed. Not when it's still open.
Mal -adjustment of the TPS upsets that function.
Also when you unplug the AFM.
In that case the ECU detects that it's un-plugged and works in Alpha N mode which uses the TPS as the load.
quote from barryboys.
Yes, yes, yes, that might be so, but you're clearly missing the bigger picture.....
4 intercoolers!!!!!!!!
Beat that!!!!
 
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ravensierra
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Location: Auckland City

Re: All you need to know about factory BOVs

Sat 03 Sep, 2016 1:52 pm

What? But turbos do spin at idle
Image
 
magn1t
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Re: All you need to know about factory BOVs

Sat 03 Sep, 2016 4:38 pm

This is my dragsport BOV, I bought it back in about 2000. It caused no end of problems in the black car as VTA. It got plumbed in properly afterwards then it got swapped into the red car so I could upgrade by going back to the proper GTO BOVs.
The rubber diaphragm split and caused a leak. I wouldn't have know if it wasn't for me trying to get the low fuel trims back to 100% then checking for leaks.
I've RTVd the split and seems to be working (for) now.

https://youtu.be/seHBPNKPnlc

Those spring clips are a fail on race day.


Here's the one which scruffy asked for.

https://www.youtube.com/watch?v=07SseGVDieg


ravensierra wrote:
What? But turbos do spin at idle


Do they?

A lighter test. The air is being sucked in.
Baby ones can spin a lot but not move much air.
These spin. My TDO5s don't.They'll move a few degrees, stop, move another half turn, stop....... etc.

https://www.youtube.com/watch?v=-3nRlZR ... e=youtu.be


Here with the EVO BOV fited, it stalled for the first time.
https://www.youtube.com/watch?v=nM90SUf ... e=youtu.be




This popped up too. Quite funny really?
People who've got no fecking idea what they're doing?
How to gain 50 HP with nothing other than guesswork.

https://www.youtube.com/watch?v=9Rh7P_8dvPc


But

The internet is full of them.
quote from barryboys.
Yes, yes, yes, that might be so, but you're clearly missing the bigger picture.....
4 intercoolers!!!!!!!!
Beat that!!!!
 
skates
Posts: 47
Joined: Fri 28 Aug, 2015 8:55 pm

Re: All you need to know about factory BOVs

Wed 07 Sep, 2016 1:00 am

Thread shouldn't really be titled all you need to know about factory BOVs, should it.
You've not surprisingly turned up some broken BOVs and turbos in the junkyard :lol:
 
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Scruffy
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Re: All you need to know about factory BOVs

Fri 09 Sep, 2016 9:02 pm

you wouldve done yourself a great service by making these vids a long time ago haha.
thanks steve. makes sense, but nice to see it on video too ;)

edit; thought that rtv in the valve was melted plastic from the lighter at first haha
"GTO's have a turbo?!"
~Mag & Turbo
 
magn1t
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Re: All you need to know about factory BOVs

Sat 10 Sep, 2016 1:13 pm

Scruffy wrote:
you wouldve done yourself a great service by making these vids a long time ago haha.
thanks steve. makes sense, but nice to see it on video too ;)

edit; thought that rtv in the valve was melted plastic from the lighter at first haha


I meant to do it a while back but people have their own eyes , they can make their own observations on their own cars...........which they don't want to do because it's too hard and it's easier just to argue on a keyboard......because some dumbarse yank said so.


Anyway........now that you can see that stalling is caused by an open BOV (in the case of a factory BOV) and air going IN rather than OUT, it should be easy to fix.
Fix as in having VTA and not stall. That just requires a 1 way valve making / adding.


In the case of over tightening the spring (what usually happens with an aftermarket VTA BOV), it stalls for a different reason which I might get a video of when the weather clears up a bit. Same as having the BOV completely blocked off.
Again , there's always going to be some clown somewhere who insists that you don't need a BOV but Mitsubishi wouldn't have made one if that was the case.
Early factory turbo cars didn't use them but they didn't use intercoolers either because they only ran a couple of pounds boost.
The more boost you run, the more essential a proper working BOV is.
quote from barryboys.
Yes, yes, yes, that might be so, but you're clearly missing the bigger picture.....
4 intercoolers!!!!!!!!
Beat that!!!!
 
magn1t
Topic Author
Posts: 2760
Joined: Mon 04 Feb, 2008 1:15 pm
Location: Upsetting the ricers on youtube 1magnit

Re: All you need to know about factory BOVs

Mon 12 Sep, 2016 1:32 pm

Here's another simple video to study.
The engine hasn't quite fully warmed up so the idle is a bit on the high side.

https://youtu.be/7BnbWl9y0vw

Plus a couple that aren't mine but worth a watch.
One shows suction, the other a leak.

https://www.youtube.com/watch?v=ndX0KSttYGQ

https://www.youtube.com/watch?v=6bZ21i4X2S8
quote from barryboys.
Yes, yes, yes, that might be so, but you're clearly missing the bigger picture.....
4 intercoolers!!!!!!!!
Beat that!!!!
 
magn1t
Topic Author
Posts: 2760
Joined: Mon 04 Feb, 2008 1:15 pm
Location: Upsetting the ricers on youtube 1magnit

Re: All you need to know about factory BOVs

Fri 16 Sep, 2016 2:37 pm

The bucket test is quite good.
It gives a better idea of what leaks are happening.

https://youtu.be/O_iV6PIEeOg

https://youtu.be/UJ5evlF0kFs
quote from barryboys.
Yes, yes, yes, that might be so, but you're clearly missing the bigger picture.....
4 intercoolers!!!!!!!!
Beat that!!!!

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