BOV madness
lifelong learner
Joined: Jul 2000
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umm.;
No i do not have the lower one connected. Only the upper nipple.
and you are completely wrong about that.
i can have it saying 0 vaccum and running 15psi of boost
in other words i can leave all the vac niples disconnected from my bov.
and when i let off
PSHHHHHHHHHHH regardless.
No i do not have the lower one connected. Only the upper nipple.
and you are completely wrong about that.
i can have it saying 0 vaccum and running 15psi of boost
in other words i can leave all the vac niples disconnected from my bov.
and when i let off
PSHHHHHHHHHHH regardless.
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rest in peace tim.
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rest in peace tim.
TR Balla Donor Supreme
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Originally posted by "Someone"
Originally posted by v8killer
***At idle most engines make between 17-22 inHg of vacuum. So if you adjust the BOV towards hard so that it is closed at idle that means that BOV will need to be set to open at a vacuum level greater than 22 inHg. After a shift your vacuum will go to around 25-27 inHg which is just barely over the threshold of 22 inHg you have set the BOV at. This hard setting means that the BOV will open a lot later than normal which allows more time for compressor surge to occur.
You are much better off adjusting the BOV soft to open at only 10 inHg of vacuum and reroute it. So when you shift gears and create 25-27 inHg of vacuum you are way above the threshold to open the valve. Thus the valve opens early and quickly negating the chance of experiencing compressor surge.
Originally posted by v8killer
***At idle most engines make between 17-22 inHg of vacuum. So if you adjust the BOV towards hard so that it is closed at idle that means that BOV will need to be set to open at a vacuum level greater than 22 inHg. After a shift your vacuum will go to around 25-27 inHg which is just barely over the threshold of 22 inHg you have set the BOV at. This hard setting means that the BOV will open a lot later than normal which allows more time for compressor surge to occur.
You are much better off adjusting the BOV soft to open at only 10 inHg of vacuum and reroute it. So when you shift gears and create 25-27 inHg of vacuum you are way above the threshold to open the valve. Thus the valve opens early and quickly negating the chance of experiencing compressor surge.
you are missing one very big point in your post here...A BOV operates on the premise of pressure differential. when the pressure differential between the intake plumbing and the manifold is greater than the set point the valve will open.
granted set up like it is my BOV may not open until 22 inHg of pure vacuum to prevent leaks at idle. I also agree that when i shift there will be greater than 25 inHg in the manifold but you forget that there is also 14 p.s.i. (28.504 inHg of pressure) pressing on the head of the valve forcing it to open.
So for arguments sake lets say that the valve head has an area that is .75 that of the vacuum diaphram (area of 1). you get an effective pressure differential of
(25 * 1) + (28.5 * .75) = 46.375
this is more than enough to open my valve set @ 22 inHg
but for a more practical sake lets see how shell do just crusing around town at low boost of say 3 p.s.i. (6.108 inHg) on the highway at part throttle.
(25 * 1) + (6.108 * .75) = 29.581
Again plenty to open the valve. So i really dont see how setting the valve to stay closed at idle can hurt that much?
Its like this for me...I like it venting to the atmosphere. If the t-25 is to fragile to handle a stiffly set BOV then its a piece of crap as far as a PERFORMANCE turbo goes. Im not worried about it...
EDIT: to further this discussion (because i know someone other than Jay will ask..) the reason that the BOV will not open under Wide Open Throttle due to the 14 p.s.i. is that the diaphram is pushing the valve back closed with approxamately the same pressure that the intake piping is putting on the valve head. remember the top line into a BOV should supply boost as well as vaccum to the diaphram.
(-28.5 * 1) + (28.5 *.75) = -7.125
the minus represents force that is acting to keep the vlave closed on top of the pressure that is being applied by the spring that we are adjusting.
END EDIT
Scott
lifelong learner
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exactly.
boost+spring > boost. so it always stays closed even without a very stiff spring.
but
o vaccum + spring < boost so the boost opens it. word.
boost+spring > boost. so it always stays closed even without a very stiff spring.
but
o vaccum + spring < boost so the boost opens it. word.
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Upon further review....
I do believe that some of the terminology that is being thrown around here might be a little off. setting a blow off valve so such that it opens at such low vaccum pressures almost makes it behave more like a bypass valve (BPV). In my book this is far different than a blowoff valve (BOV). Vortec offers 2 different models of their BOV...the true BOV non adjustable at 16 inHg and the BPV adjustable between 3 and 12 inHG. my SR would barely run without stalling with the BPV vented to the atmosphere and set to MAXIMUM stiffness. i put on a greddy R BOV in its place...and no problems.
set it up how you like (BOV vs. BPV)...im sick of kicking this horse laying here dead at my feet...but i was just throwing this out as food for thought to get some other takes...
Scott
I do believe that some of the terminology that is being thrown around here might be a little off. setting a blow off valve so such that it opens at such low vaccum pressures almost makes it behave more like a bypass valve (BPV). In my book this is far different than a blowoff valve (BOV). Vortec offers 2 different models of their BOV...the true BOV non adjustable at 16 inHg and the BPV adjustable between 3 and 12 inHG. my SR would barely run without stalling with the BPV vented to the atmosphere and set to MAXIMUM stiffness. i put on a greddy R BOV in its place...and no problems.
set it up how you like (BOV vs. BPV)...im sick of kicking this horse laying here dead at my feet...but i was just throwing this out as food for thought to get some other takes...
Scott
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boost+spring > boost. so it always stays closed even without a very stiff spring.
***Exactly. It is just like a simple arithmetic equation.
boost pressure (IC) + spring pressure > boost pressure (manifold)
The boost pressures cancel each other out. The only thing left over holding the valve closed is the force of the spring. We are in agreement on this point. Even a very light spring is enough to keep the valve closed under high boost pressures.
o vaccum + spring < boost
***The above equation makes no sense at all. You are saying that on your very special BOV you can have none of the nipples attached and the BOV will operate correctly. You must have a magic BOV then.
Lets assume you are running the BOV with *neither* of the nipples attached. Then under boost you will have the following:
boost pressure (IC) > spring pressure
If you have a street spring adjusted softly the valve will be open under boost during acceleration. This is not desirable.
If you have a race spring adjusted stiff then the valve will be closed under certain boost levels. Then when you shift gears the valve will still not open. What force will act to open the valve if you do not supply vacuum to the upper nipple?
Why is there such a big debate on how to hook up a BOV or how to adjust it? This thread has been around forever on several message boards and there are so many opinions. The correct answer is never revealed.
Well here it is:
For a bypass valve rerouted to the intake on a MAF equipped car set the valve to open easily at around 10-15 inHg of vacuum.
For a bypass valve (or BOV) open to atmosphere on a MAF equipped car set it to open at greater than 22 inHg so that it is closed at idle.
For a BOV on a MAP based car open to atmosphere set it to open at greater than 22 inHg or set it soft to open at 10-15 inHg and use a small air filter on the BOV so as to not allow unclean air into the BOV under vacuum conditions like during part throttle cruise.
Of course there one last way I do it on MAF cars. I set the spring to open soft at 10 inHg with a street spring. With a Type S I use only the inner spring and discard the outer one. Attach the upper nipple to vacuum. Attach the lower nipple to a boost signal that is regulated by an on/off solenoid which allows boost to reach the lower nipple only when the throttle is closed. Use a microswitch attached to the throttle body linkage or a circuit that monitors TPS voltage to open/close the solenoid. This way will cause the valve to open even faster and the blow off sound will be louder as well.
Next.
***Exactly. It is just like a simple arithmetic equation.
boost pressure (IC) + spring pressure > boost pressure (manifold)
The boost pressures cancel each other out. The only thing left over holding the valve closed is the force of the spring. We are in agreement on this point. Even a very light spring is enough to keep the valve closed under high boost pressures.
o vaccum + spring < boost
***The above equation makes no sense at all. You are saying that on your very special BOV you can have none of the nipples attached and the BOV will operate correctly. You must have a magic BOV then.
Lets assume you are running the BOV with *neither* of the nipples attached. Then under boost you will have the following:
boost pressure (IC) > spring pressure
If you have a street spring adjusted softly the valve will be open under boost during acceleration. This is not desirable.
If you have a race spring adjusted stiff then the valve will be closed under certain boost levels. Then when you shift gears the valve will still not open. What force will act to open the valve if you do not supply vacuum to the upper nipple?
Why is there such a big debate on how to hook up a BOV or how to adjust it? This thread has been around forever on several message boards and there are so many opinions. The correct answer is never revealed.
Well here it is:
For a bypass valve rerouted to the intake on a MAF equipped car set the valve to open easily at around 10-15 inHg of vacuum.
For a bypass valve (or BOV) open to atmosphere on a MAF equipped car set it to open at greater than 22 inHg so that it is closed at idle.
For a BOV on a MAP based car open to atmosphere set it to open at greater than 22 inHg or set it soft to open at 10-15 inHg and use a small air filter on the BOV so as to not allow unclean air into the BOV under vacuum conditions like during part throttle cruise.
Of course there one last way I do it on MAF cars. I set the spring to open soft at 10 inHg with a street spring. With a Type S I use only the inner spring and discard the outer one. Attach the upper nipple to vacuum. Attach the lower nipple to a boost signal that is regulated by an on/off solenoid which allows boost to reach the lower nipple only when the throttle is closed. Use a microswitch attached to the throttle body linkage or a circuit that monitors TPS voltage to open/close the solenoid. This way will cause the valve to open even faster and the blow off sound will be louder as well.
Next.
lifelong learner
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not really.
the only thing i was arguing for was whether or not the maf throws in fuel when you let off the throttle.
i was right in that it only does from the periopd of 100% to 0% but not past 0%.
and yes
my blow off vavle blows open with nothing attached to it.
thats why i attach the upper thing
otherwise it blows open at 16psi.
the only thing i was arguing for was whether or not the maf throws in fuel when you let off the throttle.
i was right in that it only does from the periopd of 100% to 0% but not past 0%.
and yes
my blow off vavle blows open with nothing attached to it.
thats why i attach the upper thing
otherwise it blows open at 16psi.
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i wanna go fast
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Ok i refuse to read all the other posts in this thread...skip it and get to my opinion.
BOV has 3 functions:
1. release excess pressure in the turbo piping when the throttle plate closes abruptly protecting the life the turbo by reducing the extra pressure created by this.
2. during a shift allowing the excess pressure to be released. when this is done there is no longer pressure working against the turbo allowing it to continue spinning without the extra pressure slowing the wheel down.
3. make cool sounds during shifting
Now a BOV and recirc are essentially one in the same. They open to relieve pressure from the turbo piping. A stock recirc or a BOV with a recirc line routes the excess pressure created back into the intake piping...after the MAF/MAS before the turbo. Since the air has been metered it needs to be kept in the system.
With an aftermarket BOV or a disconnected recirc the excess pressure is released into the atmosphere.
A stock recirc remains open when it sees vacuum from the manifold. This occurs when the throttle plate is closed enough (during a shift idle etc). An aftermarket BOV does the same thing but can be adjusted to how much it is open at vacuum and can be adjusted so it stays shut at idle. With the BOV setup like that the only time it will open and relieve any pressure is when there is boost in the piping and vacuum from the manifold (bascially only from shifting gears or abruptly lifting throttle).
Nissans eclipsestoyotas etc use maf/mas devices. They are not happy when they vent atmosphere during idle or low throttle activities.
Like said before the air is calculated by the maf the air escapes to atmosphere causing the vehicle to go rich dumping extra fuel. It is completely noticeable at idle low throttle driving and sometimes between a shift (depending on how much air is escaping.
Do yourself a favor hook it up in recirc and it will still be loud as hell. The greedy type-s on my Z must remain closed at idle and it only opens a little during shifts to release some of the pressure. Recirc would be the preferred setup.
BOV has 3 functions:
1. release excess pressure in the turbo piping when the throttle plate closes abruptly protecting the life the turbo by reducing the extra pressure created by this.
2. during a shift allowing the excess pressure to be released. when this is done there is no longer pressure working against the turbo allowing it to continue spinning without the extra pressure slowing the wheel down.
3. make cool sounds during shifting
Now a BOV and recirc are essentially one in the same. They open to relieve pressure from the turbo piping. A stock recirc or a BOV with a recirc line routes the excess pressure created back into the intake piping...after the MAF/MAS before the turbo. Since the air has been metered it needs to be kept in the system.
With an aftermarket BOV or a disconnected recirc the excess pressure is released into the atmosphere.
A stock recirc remains open when it sees vacuum from the manifold. This occurs when the throttle plate is closed enough (during a shift idle etc). An aftermarket BOV does the same thing but can be adjusted to how much it is open at vacuum and can be adjusted so it stays shut at idle. With the BOV setup like that the only time it will open and relieve any pressure is when there is boost in the piping and vacuum from the manifold (bascially only from shifting gears or abruptly lifting throttle).
Nissans eclipsestoyotas etc use maf/mas devices. They are not happy when they vent atmosphere during idle or low throttle activities.
Like said before the air is calculated by the maf the air escapes to atmosphere causing the vehicle to go rich dumping extra fuel. It is completely noticeable at idle low throttle driving and sometimes between a shift (depending on how much air is escaping.
Do yourself a favor hook it up in recirc and it will still be loud as hell. The greedy type-s on my Z must remain closed at idle and it only opens a little during shifts to release some of the pressure. Recirc would be the preferred setup.
