Does your BOV vent at idle?
03-11-2013, 11:13 PM
#1
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Does your BOV vent at idle?
Not too long ago, I purchased another Maxima with a supercharger on it. It came with a Blitz BOV, like what a lot of fellas on here use. It didn't vent at idle. No matter how much I played with the adjustment screw, it still wouldn't vent (Yes, I read the Blitz instructions...).So I figured it was defective. I happen to have a few extra Blitz BOV's that I've acquired over the years and tried those too. No luck, they don't vent at idle either. All in all, I've tried 5, count 'em 5, different Blitz BOV's and none of them vent at idle. Could all 5 be defective? I highly doubt that. IMO, the spring in the BOV is way too strong.
My Vortech Race BOV/BPV, on the other hand, vents like crazy at idle. Same goes for the original Bosch BOV/BPV included in the original Stillen kit.
For those of you with the Blitz BOV, does yours vent at idle? If so, a lot or a little?
For other different BOV users, please list what BOV you have and how much it vents (if any) at idle.
My Vortech Race BOV/BPV, on the other hand, vents like crazy at idle. Same goes for the original Bosch BOV/BPV included in the original Stillen kit.
For those of you with the Blitz BOV, does yours vent at idle? If so, a lot or a little?
For other different BOV users, please list what BOV you have and how much it vents (if any) at idle.
03-14-2013, 07:01 AM
#3
By venting at idle, do you mean if you rev it at idle you cannot hear the blow off vent? If so, mine doesnt either. Or does it really low. I ran a few days with the hood off while doing the turbo setup on my ride and I could barely hear the blow off when reving the engine... I can hear the pulsing of the blow off in the exhaust note though(if that makes sense). With the hood on, I don't hear it at all.
03-14-2013, 05:01 PM
#4
bov venting at idle
I was giving this some thought...If the bov supposed to vent at idle doesnt that mean it should be open all the time? Since the SC is constantly making boost because the engine is always moving the blower. This how these bov supposed to work for SC applications? If this is not the case compressor surge would be the result. Am I right on any of this?
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03-14-2013, 05:18 PM
#5
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By venting at idle, do you mean if you rev it at idle you cannot hear the blow off vent? If so, mine doesnt either. Or does it really low. I ran a few days with the hood off while doing the turbo setup on my ride and I could barely hear the blow off when reving the engine... I can hear the pulsing of the blow off in the exhaust note though(if that makes sense). With the hood on, I don't hear it at all.
I was giving this some thought...If the bov supposed to vent at idle doesnt that mean it should be open all the time? Since the SC is constantly making boost because the engine is always moving the blower. This how these bov supposed to work for SC applications? If this is not the case compressor surge would be the result. Am I right on any of this?
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At idle, and cruising, there is no boost and there is negative pressure (vacuum). At idle, the throttle body plate is virtually 100% closed. The air from the blower needs to go somewhere in order not to come back and create compressor surge. That somewhere is out the BOV.
03-14-2013, 06:25 PM
#6
No, no revving. Just simply letting the car idle w/o touching the gas pedal or anything. Since you're turbo, I believe you're ok but I'm not positive. SC, not so much. A BOV that's not venting at idle is causing compressor surge.
No, it needs to be closed under boost and open at idle. If it was open at WOT, no boost would be created and there would be no additional power. Think of an open BOV at WOT like a leak in a pipe. There would be a loss in pressure (ie boost) and a therefore a loss in power.
At idle, and cruising, there is no boost and there is negative pressure (vacuum). At idle, the throttle body plate is virtually 100% closed. The air from the blower needs to go somewhere in order not to come back and create compressor surge. That somewhere is out the BOV.
No, it needs to be closed under boost and open at idle. If it was open at WOT, no boost would be created and there would be no additional power. Think of an open BOV at WOT like a leak in a pipe. There would be a loss in pressure (ie boost) and a therefore a loss in power.
At idle, and cruising, there is no boost and there is negative pressure (vacuum). At idle, the throttle body plate is virtually 100% closed. The air from the blower needs to go somewhere in order not to come back and create compressor surge. That somewhere is out the BOV.
Wiz, what was wrong with all those blitz you had? Doesnt seem normal to have 5 faulty one's. Maybe wrong application?
03-14-2013, 06:48 PM
#7
I don't think venting or not venting at idle is an issue as long as it does its job when it really counts, and that is to prevent compressor surge after the throttle plate closes. If there is surge I would be worried but not if it vents or does not vent at idle. Compressor surge to some degree is ok even at higher rpms, if that is what you are worried about. Then imagine the vacuum pressure it takes to operate a bov, this is only present at rpms way higher than idle.
03-15-2013, 03:07 PM
#8
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I've been told that you don't want the BOV to open at idle. You need to adjust the spring tension to the lightest point where it will *just* not open under the highest vacuum your motor makes. Then the vacuum doesn't pull it open, the boost pushes it open when there's not compensating boost coming from the signal line.
I would suspect that if your BOV is venting at idle, it's probably not sealing really well under boost.
I would suspect that if your BOV is venting at idle, it's probably not sealing really well under boost.
03-18-2013, 05:25 PM
#11
My turbo XS i had on my 01 vented quite a bit of air at idle. Full throttle it would close and vented between shifts. Not sure about the Blitz though. I don't think it's a good thing it doesn't vent at idle and wouldn't run it to much like that.
03-18-2013, 07:30 PM
#13
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Thanks for all your input fellas
I believe Blitz has two BOV's. Do you know which Blitz model you have?
It could be, but not in this case. The second I swapped out the Blitz for another Vortech Race BOV, it vented at idle like it should.
Another point I'd like to make, is that the original Bosch BOV that Stillen provided in their kit back in the day vents at idle, and there is no adjustment of any sort.
It's supposed to vent at idle.
It could be, but not in this case. The second I swapped out the Blitz for another Vortech Race BOV, it vented at idle like it should.
Another point I'd like to make, is that the original Bosch BOV that Stillen provided in their kit back in the day vents at idle, and there is no adjustment of any sort.
It's supposed to vent at idle.
03-18-2013, 07:32 PM
#14
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Nope. Wouldn't matter.
03-24-2013, 10:32 PM
#16
03-27-2013, 10:29 PM
#17
BOV isn't meant to vent at idle (vacuum)
Only a BPV does that. Which is what SCs should be running in most applications from my understanding. It also helps fuel economy and reliability/longevity because you're not throwing boost at the car all the time, there's only boost at low vacuum (usually 70%+ TPS) aka when you step on the gas because you wanna go fast lol.
I posted here a while ago regarding These elusive BPVs that seem to be a mystery/source of confusion. I should update that post because I've found out even more about them and the differences vs. BOV. Took a lot of digging to get decent answers lol.
http://forums.maxima.org/supercharge...ng-needed.html
Most of the more solid answers i got were from mustang forums, though there was a pile of misinformation there also.
Only a BPV does that. Which is what SCs should be running in most applications from my understanding. It also helps fuel economy and reliability/longevity because you're not throwing boost at the car all the time, there's only boost at low vacuum (usually 70%+ TPS) aka when you step on the gas because you wanna go fast lol.
I posted here a while ago regarding These elusive BPVs that seem to be a mystery/source of confusion. I should update that post because I've found out even more about them and the differences vs. BOV. Took a lot of digging to get decent answers lol.
http://forums.maxima.org/supercharge...ng-needed.html
Most of the more solid answers i got were from mustang forums, though there was a pile of misinformation there also.
Last edited by TunerMaxima3000; 03-27-2013 at 10:33 PM.
03-27-2013, 10:57 PM
#19
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BOV isn't meant to vent at idle (vacuum)
Only a BPV does that. Which is what SCs should be running in most applications from my understanding. It also helps fuel economy and reliability/longevity because you're not throwing boost at the car all the time, there's only boost at low vacuum (usually 70%+ TPS) aka when you step on the gas because you wanna go fast lol.
I posted here a while ago regarding These elusive BPVs that seem to be a mystery/source of confusion. I should update that post because I've found out even more about them and the differences vs. BOV. Took a lot of digging to get decent answers lol.
http://forums.maxima.org/supercharge...ng-needed.html
Most of the more solid answers i got were from mustang forums, though there was a pile of misinformation there also.
Only a BPV does that. Which is what SCs should be running in most applications from my understanding. It also helps fuel economy and reliability/longevity because you're not throwing boost at the car all the time, there's only boost at low vacuum (usually 70%+ TPS) aka when you step on the gas because you wanna go fast lol.
I posted here a while ago regarding These elusive BPVs that seem to be a mystery/source of confusion. I should update that post because I've found out even more about them and the differences vs. BOV. Took a lot of digging to get decent answers lol.
http://forums.maxima.org/supercharge...ng-needed.html
Most of the more solid answers i got were from mustang forums, though there was a pile of misinformation there also.
Had it. Hated it. Sold it. Doesn't vent at idle. I love it though on my turbo Supra.
03-27-2013, 11:00 PM
#20
03-27-2013, 11:07 PM
#21
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I couldn't be happier with my Vortech Race BPV... no whistle or sound though if that matters to you.
03-28-2013, 09:08 AM
#23
The best way to find out is always ask the manufacture. If Vortech says the BOV should vent at idle because of compressor surge then that's what your BOV should do. I'm speaking of SC applications.
03-28-2013, 10:11 AM
#25
03-29-2013, 01:11 PM
#28
When I had the Tial, I would get surge when cruising on the highway, give it a little bit of gas and it would go away, let up and it would come back.
The Tial isnt a truly adjustable BOV, it does have interchangeable springs for different vacuum pulls at idle but when I tried different springs they were either way too soft and or to stiff and wouldnt open at all at idle resulting in surging while idlleing which sounded horrible.
The Tial sounded awesome when it released boost but I couldnt deal with it surging and the thought of my blower suffering from it so I sold it and got the Mondo.
04-01-2013, 11:18 AM
#29
I'll try to get some cutaways and such together and update that thread with pertinent info. I"m swamped right now trying to get the car ready for the road and running so I can't promise a quick post there but I'll drop in here as much as possible (now subscribed)
The only thing that vents at idle is a BPV. They are NOT the same thing.
If we're trying to understand the BPV and why/how it works, we cannot confuse a BOV and BPV. The terms must be used precisely.
A BOV will NOT vent at idle.
------------------------------
Ramble time:
Surge is caused when the incoming boost hits a suddenly closed throttle plate (let off the gas).
Not cited/copied information, just my knowledge, grain of salt:
In a Turbo setup boost is created by load. When the engine is under load it creates boost proportionately to it's load (pretty much).
So you're under load, chugging along, seeing boost, and you suddenly let off the throttle, the charge pipes still have boost and the turbo will KEEP creating boost until it slows down naturally, even though you've eliminated the load (driving force).
Because of this you need to vent the charge pipe boost out of the pipe otherwise the pressure will cause reverberations against the closed throttle plate and create pressure waves that could damage the throttle plate and potentially the turbo.
This is done with a BOV. The only time you need to vent a turbo setup is after boosting and suddenly closing the throttle.
Turbo cliffs:
Turbos create boost based on load. Load is directly proportionate to throttle position and thus, vacuum. When there is no load, boost dies off.
SUPERCHARGER
In a supercharger setup boost is created by RPM. Boost at the blower is directly controlled by RPM and nothing else.
As soon as RPM drops, boost IMMEDIATELY drops with it. There is no 'spin down time' for the SC, it's directly connected and slows down as fast as the Engine RPM.
This is why we need a BPV. A BPV vents the boost that will be created at higher RPM.
For instance you can be easily be cruising at 3000 RPM but be under little to no load (under vacuum) if you're in a lower gear.
At this time, without a BPV, you would be creating roughly HALF the available boost in the engine. That's a lot of boost with the throttle plate barely open, and no real load on the engine.
The engine wont' be able to take that much boost. This causes the same situation we talked about before with a turbo, pressure waves, reverberation, yadda, yadda, the end result is stress on the supercharger, causing accelerated wear and often causing throttle plate noise/wear as well.
This is not as severe as when you're under high-boost and need that blow-off when shifting, that's higher boost vs. a completely closed throttle plate, obviously more severe.
However, it IS STILL an issue you don't want to ignore. And it WILL wear components faster than desired.
part 2:
The BPV comes in here. It vents that unwanted boost under vacuum. That's it. Plain and simple. Basically, any positive pressure in the charge pipe is vented until you open the throttle 70%+
Under high boost the BPV works the same way a BOV does, it blows off the high pressure.
SUPERCHARGER CLIFFS:
Superchargers build boost by RPM, and RPM only.
You don't want boost unless the engine is under load and the throttle is open (you are trying to Ricky Bobby)
The BPV vents boost at low engine load, even if the engine RPM is high and the SC is making boost.
Venting the boost you don't want with a Supercharger saves the blower, stops fluttering at low load, high RPM situations, and saves fuel economy and accelerated engine wear (especially on engines that aren't built for boost)
Those above 3 points are the main reasons you want a BPV. And a BOV WILL NOT WORK to accomplish this task.
04-11-2013, 12:41 AM
#30
I didn't want to say this earlier but I took my bov apart and lubed it with M1 and it worked a lot better. It's a blitz DD and I also asked this same question on here and everyone was stumped.
10-03-2013, 05:06 AM
#31
I know im late to talk about this but here's some info on my bypass valve.
I have a vortech Maxflow mando bypass and this thing is huge and the sound is amazing it sounds like u have twin chargers very loud whistle,and it vents at idle it feels like the blower its self just sitting at idle alot of air u can cool ur self down with it lol.For example if on 1st gear and u run the to about 6000rpm and u let off the gas u hear the bypass venting all the way down rpm which ididnt understand at first cause never really seen supercharged around my way just mainly turbo so after reading this thread it explains why.
I have a vortech Maxflow mando bypass and this thing is huge and the sound is amazing it sounds like u have twin chargers very loud whistle,and it vents at idle it feels like the blower its self just sitting at idle alot of air u can cool ur self down with it lol.For example if on 1st gear and u run the to about 6000rpm and u let off the gas u hear the bypass venting all the way down rpm which ididnt understand at first cause never really seen supercharged around my way just mainly turbo so after reading this thread it explains why.
Last edited by Max streets; 10-03-2013 at 05:09 AM.
10-05-2013, 11:27 AM
#34
The only difference between a BOV and a BPV is that BPVs are recirculated. ALL recirculated BOVs are bypass valves. They are called Blow Off valves when they blow off the extra pressure into the atmosphere.
The confusion in terminology arises through the two different types of Valves.
1) Push Types
2) Pull Types
1) Push Type Valves are closed until the pressure against it is stronger than the spring holding it closed. Basically The TB plate closes, all the pressure is in the pipe and it's stronger than the Spring and it therefore vents.
2) Pull type BOVs are pulled close by the pressure flowing through them. They are open under vacuum conditions. Once vacuum diminishes and pressure builds they hold close.
quotes copied from some evo forum.
I am personally running the Synchronic Synapse BOV ( and it is called BOV by the manufacturer and everybody else) which is a pull-type BOV. It is open at idle and under light acceleration. As soon I hit approximately 15%-20% throttle it closes and stays closed.Here's a video showing how it operates.
edited for better video
The confusion in terminology arises through the two different types of Valves.
1) Push Types
2) Pull Types
1) Push Type Valves are closed until the pressure against it is stronger than the spring holding it closed. Basically The TB plate closes, all the pressure is in the pipe and it's stronger than the Spring and it therefore vents.
The push type blow off valve stays closed under vacuum conditions by a spring that is inside it pushing against the main valve that opens and closes. The spring has a rated pressure level on it that will not allow the valve to be open until a certain pressure level is achieved. The little nipple that you see on the side of the push-type blow-off valve is attached directly to the intake manifold via vacuum hose and shows the valve vacuum pressure at idle. When the vehicle is on-boost, the nipple shows positive pressure and that pushes the diaphragm closed which allows boost to build up inside the piping. Since the positive pressure in the intake manifold equals the positive pressure in the intake pipe, the valve remains closed until the throttle body closes and vacuum is applied to the blow-off valve, allowing the pressure built up in the piping to push it's way out of the piping past the valve to the atmosphere. This rush of air exits out the vent port, and depending on the structural configuration of the vent port, it can make a very unique sound. I personally do not like this type blow-off valve, as it is prone to leakage like a ******'s ***, is slow to respond and requires rebuild from time to time. The adjustment nut on most of these valves allows the user to adjust the stiffness of the spring to their personalized settings. Much like Pandora's box, this was a bad ****ing idea. The root of 'BOV tuning' came from this adjustment nut. So now any ****head with a wrench and an allen key could 'tune' a blow-off valve. Beautiful. And I thought the Tactrix cable was a bad idea.
http://www.youtube.com/watch?v=Ls5fi...read.php?t=189
http://www.youtube.com/watch?v=Ls5fi...read.php?t=189
The other type of blow-off valve is the pull-type blow off valve. I find this valve to be vastly superior to the push-type valve for many reasons. Number one, the valve is held closed in place by the actual boost pressure in the pipe, not the line that feeds from the intake manifold. You'll never have a leaking issue with this one at higher boost levels because of a compromised diaphragm in a push-type blow-off valve. When the car is on boost, the valve stays shut all the way, 100%, as the positive boost pressure on the pull valve helps ensure that the valve is shut on boost. When the throttle body is closed, vacuum pressure is immediately applied to the pull valve and the pressurized air escapes immediately. I will personally be replacing my Tial push type valve for an HKS race valve in the near future and I feel I will get some really good response from this as well as a reduction in surge, although my compressor housing is already setup with an anti-surge feature.
I am personally running the Synchronic Synapse BOV ( and it is called BOV by the manufacturer and everybody else) which is a pull-type BOV. It is open at idle and under light acceleration. As soon I hit approximately 15%-20% throttle it closes and stays closed.Here's a video showing how it operates.
edited for better video
Last edited by McSteve; 10-05-2013 at 11:50 AM.
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