BOV Setup for your N54

doublespaces

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That horrible screeching sound from the BOV is what I really hate.....

The screeching sound is created when your bov doesn't open fully (or soon enough), and the boost hits the surge line. The air reverts back toward your intake filter and gets chopped up by the compressor blades on the way out and combined with the new material of your inlets, that is making the squealing sound similar to the party toys.

Here is a video, notice how that sound occurs before the plunger opens:

As for the fluttering, that problem is a little more complicated but what is certain is you have a 7+ psi pressure differential between your intake manifold and your chargepipe. If not a hardware issue, that indicates WGDC being too high in my opinion, but I'm no tuner. Being an OTS tune doesn't really debunk that issue, because I see this question come up regularly when people upgrade the inlets specifically. Which tells me the problem already existed but weren't aware of it.
 

Jeffman

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Jan 7, 2017
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Honestly, the BOV flutter concerns me less than the horrible noise the BOV is making. If I put the slightly heavier BOV spring in (10psi), the flutter goes away. It's not compressor flutter. The car ran great with the heavier 10psi spring in the BOV.....it opened with just a slight about of pedal input and decrease in vacuum. This lighters 6-7psi black spring is wide open and idle, and technically...it's to light. I could probably try shimming it a bit to get it just slightly closed at idle. Who knows, a little more pressure on the spring might get rid of the fluttering also.
This is my experience too with my Tial-Q BOV. 10psi spring works great. 8psi gives me flutter
 
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IQraceworks

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The screeching sound is created when your bov doesn't open fully (or soon enough), and the boost hits the surge line. The air reverts back toward your intake filter and gets chopped up by the compressor blades on the way out and combined with the new material of your inlets, that is making the squealing sound similar to the party toys.

Here is a video, notice how that sound occurs before the plunger opens:

As for the fluttering, that problem is a little more complicated but what is certain is you have a 7+ psi pressure differential between your intake manifold and your chargepipe. If not a hardware issue, that indicates WGDC being too high in my opinion, but I'm no tuner. Being an OTS tune doesn't really debunk that issue, because I see this question come up regularly when people upgrade the inlets specifically. Which tells me the problem already existed but weren't aware of it.

I don't know how the BOV couldn't be opening fast enough....it's got a 7psi spring in it that's technically too light signs it's open at idle, and with the large 1/4" ID line running from the manifold direcly to the BOV...it's got a good vacuum signal.

ALSO...remember, it didnt' make that sound with the stock inlets, only after I installed the silicone inlets. That doesn't make any sense to me at all.
 

IQraceworks

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This is my experience too with my Tial-Q BOV. 10psi spring works great. 8psi gives me flutter

Yeah, I'm probably going to put that 10psi spring back in. That flutter is annoying, more annoying than the screeching sound the BOV now makes with the silicone inlets.
 

doublespaces

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I don't know how the BOV couldn't be opening fast enough....it's got a 7psi spring in it that's technically too light signs it's open at idle, and with the large 1/4" ID line running from the manifold direcly to the BOV...it's got a good vacuum signal.

ALSO...remember, it didnt' make that sound with the stock inlets, only after I installed the silicone inlets. That doesn't make any sense to me at all.

The stock inlets aren't the same material that are less flexible and have different acoustic properties.. Doesn't mean it wasn't happening. Maybe you have weak/collapsing vacuum lines or don't have a perfect seal on the hoses, etc there could be a number of reasons you haven't ruled out. Go stick a camera down there and rev it or even better go for a drive. Don't forget that these cars use a drive by wire throttle blade. It doesn't necessarily open up as soon as you might think, particularly when you're driving.
 

fmorelli

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My money is on an install issue. Latter sucks if on e9x because it is hard to get to on the rear install.

If you do take the inlets off, I recommend a small amount of grease (I use white lube) on the inside of the inlet to abate any binding.

As you pointed out car runs fine. Corresponds with off-throttle issue. Seems like a remove, inspect, etc scenario at this point. Good luck and keep us posted!
 

doublespaces

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My money is on an install issue. Latter sucks if on e9x because it is hard to get to on the rear install.

If you do take the inlets off, I recommend a small amount of grease (I use white lube) on the inside of the inlet to abate any binding.

As you pointed out car runs fine. Corresponds with off-throttle issue. Seems like a remove, inspect, etc scenario at this point. Good luck and keep us posted!

Some people would prefer to force the bov closed and cover up the problem. Reality is, I don't necessarily blame them if it runs fine it doesn't really even matter. Vehicles are a wear item with a limited lifespan and if the defect creatse a negligible difference in life span then pulling hair out over it isn't worthwhile. But it still doesn't change the fact that something isn't operating correctly.
 

IQraceworks

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My money is on an install issue. Latter sucks if on e9x because it is hard to get to on the rear install.

If you do take the inlets off, I recommend a small amount of grease (I use white lube) on the inside of the inlet to abate any binding.

As you pointed out car runs fine. Corresponds with off-throttle issue. Seems like a remove, inspect, etc scenario at this point. Good luck and keep us posted!
I will double check them, but the install went pretty easy. I had the subframe out of the way, so it was easy to get up under there and make sure the inlets were all the way on, and the clamps went on nice and even. They are 1.75" inlets, so they fit perfectly. No crazy bends or kinks....everything lined up fine. Sliding a hose over a turbo flange, and then tightening down a clamp to hold it on....doesn't sound like a thing you could screw up even if you tried.

The thing I'm still trying to figure out is that if it is something with the inlets that is causing the noise.....that noise would have to go through the turbos, through the FMIC, back out through the chargepipe, and then out the BOV when it dumps. I find it hard to believe that the noise is coming from the inlets.......but it obviously has to be reliated to the inlets somehow since the noise started as soon as they were installed.

I will take a video of the BOV venting. I don't think there is an issue with it not opening correctly...I can put a vacuum pump on it, and it starts to open around 14in/hg, and is fully open by around 18in/hg. My motor pulls 18in/hg vacuum at idle, so the BOV is wide open when it's idling. I pulled it apart, it's clean, and operates nice and smooth.

I will try to get some logs, maybe it will help show what's going on.
 
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Torgus

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I will double check them, but the install went pretty easy. I had the subframe out of the way, so it was easy to get up under there and make sure the inlets were all the way on, and the clamps went on nice and even. They are 1.75" inlets, so they fit perfectly. No crazy bends or kinks....everything lined up fine. Sliding a hose over a turbo flange, and then tightening down a clamp to hold it on....doesn't sound like a thing you could screw up even if you tried.

The thing I'm still trying to figure out is that if it is something with the inlets that is causing the noise.....that noise would have to go through the turbos, through the FMIC, back out through the chargepipe, and then out the BOV when it dumps. I find it hard to believe that the noise is coming from the inlets.......but it obviously has to be reliated to the inlets somehow since the noise started as soon as they were installed.

I will take a video of the BOV venting. I don't think there is an issue with it not opening correctly...I can put a vacuum pump on it, and it starts to open around 14in/hg, and is fully open by around 18in/hg. My motor pulls 18in/hg vacuum at idle, so the BOV is wide open when it's idling. I pulled it apart, it's clean, and operates nice and smooth.

I will try to get some logs, maybe it will help show what's going on.

Can you borrow a CP from a friend that has a different BOV? IIRC some people said the noise goes away with a different BOV?
 

NoQuarter

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I'm wondering if the noise isn't coming from the BOV directly. Another connection that is allowing the pressure to escape at the same time the BOV is opening. Like letting air out of a balloon and it squeals... A cracked pipe or loose fitting.
 

IQraceworks

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Can you borrow a CP from a friend that has a different BOV? IIRC some people said the noise goes away with a different BOV?

Yeah, most threads I've read where guys have had this same issues with the horrible sound after installing inlets.....all had the Tial BOV's. Most also said that when they switched over to a Turbosmart BOV, the high pitched squealing noise went away. I just don't know if I want to spend $260+ just because of the sound.

I thought about taking my Tial BOV off and taking a small jewelers file to the exhaust ports that surround the plunger, and smoothing out all of the sharp machined edges. I can see a sharp edge there causing that whistling sound. It's not going to hurt anything, but it might affect how it sounds. Maybe if I'm bored and have nothing else going on one of these nights.

 

IQraceworks

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I'm wondering if the noise isn't coming from the BOV directly. Another connection that is allowing the pressure to escape at the same time the BOV is opening. Like letting air out of a balloon and it squeals... A cracked pipe or loose fitting.
Yes...that's always a possibility. I need to put a gopro camera under the hood and take the car for drive....get some good video of what's actually going on.
 

doublespaces

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Oct 18, 2016
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The thing I'm still trying to figure out is that if it is something with the inlets that is causing the noise.....that noise would have to go through the turbos, through the FMIC, back out through the chargepipe, and then out the BOV when it dumps. I find it hard to believe that the noise is coming from the inlets.......but it obviously has to be reliated to the inlets somehow since the noise started as soon as they were installed.

How do you figure? The air only needs to go out the inlets and out your air box/filter which is a pretty short path. Once your turbo surges, the compressor might still be spinning but there isn't a perfect seal and the air flow can revert back out the inlets. I used different inlets in this example because its easier to draw:
1619717376378.png



I will take a video of the BOV venting. I don't think there is an issue with it not opening correctly...I can put a vacuum pump on it, and it starts to open around 14in/hg, and is fully open by around 18in/hg. My motor pulls 18in/hg vacuum at idle, so the BOV is wide open when it's idling. I pulled it apart, it's clean, and operates nice and smooth.

I will try to get some logs, maybe it will help show what's going on.

That alone doesn't really disprove my points though, but that does show the bov is functional. The bov can open with zero vacuum, there just needs to be a ~7psi pressure differential between the intake manifold and the charge pipe. This can happen when your turbos are still boosting while the throttle blade is not fully closed and is creating an air flow restriction which can happen during part throttle and potentially immediately after you let off the accelerator which may explain some of your fluttering. The throttle blade has a mind of its own and can close in multiple steps. I believe this is also why some people get a double blow off sound.

Additionally, the vacuum your car pulls at idle is not the vacuum you'll necessarily see while driving. Even turning on the air conditioning can impact the vacuum your engine produces. But in my experience, you'll actually create just as much or more vacuum upon decel. But part throttle is a different scenario, your engine is likely producing zero engine vacuum and a little positive pressure, but the bov can still open due to what I mentioned above.

To your point, perhaps you could actually have too much vacuum for the type of lines you're using and they are collapsing, restricting the amount of vacuum actually making it to your bov. My theory still has some legs :)
 

IQraceworks

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All good points....I guess it really depends on if the sound is coming out of the intake/air filters, or if it's coming out of the actual BOV. I have the motor apart right now (changing the valve cover), but I should be done with that tonight and ready to do some more testing on it soon. I will get my gopro and take some good video....maybe it will give a better idea on where the sound is actually coming from.

As far as the line going to the BOV...it's a hard nylon push-to-connect type hose, it's not collapsing off of 20in/hg of vacuum.
 
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IQraceworks

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Here is a log I did this morning on the way to work. 70mph on the highway, 6th gear. As I started rolling into the throttle a little bit I could hear the BOV start to do it's fluttering thing. It looks like the WGDC is jumping all over the place ....not sure if that's the cause, or the affect of the BOV fluttering. Not sure what that strange throttle closure is at the start when I roll onto the gas....maybe tracking controll kicking in? strange.

If I give the car more throttle or less throttle the fluttering goes away. I pretty much have to try to get it to flutter. It didn't do that with the 10psi spring in it. Just wondering what's causing it.

https://datazap.me/u/iqraceworks/log-1619783684?log=0&data=2-3-4-19-20-21
 
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doublespaces

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Here is a log I did this morning on the way to work. 70mph on the highway, 6th gear. As I started rolling into the throttle a little bit I could hear the BOV start to do it's fluttering thing. It looks like the WGDC is jumping all over the place ....not sure if that's the cause, or the affect of the BOV fluttering. Not sure what that strange throttle closure is at the start when I roll onto the gas....maybe tracking controll kicking in? strange.

If I give the car more throttle or less throttle the fluttering goes away. I pretty much have to try to get it to flutter. It didn't do that with the 10psi spring in it. Just wondering what's causing it.

https://datazap.me/u/iqraceworks/log-1619783684?log=0&data=2-3-4-19-20-21

Don't know if I mentioned this to you before, but you know we have a datalogs section right? Also, if you're using MHD, then you can upload directly to it without transfering any files. Just swipe to the side and click upload to spoolstreet and it will appear here.
 

IQraceworks

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Here is a crummy video I took last night on my phone showing the BOV working. I don't see any real delay between throttle closure and BOV venting. You can hear that hooting sound a little bit...it's much louder when it's venting more boost. I was just doing a little easy power breaking to build boost....

As you can see...that 7psi spring really is too light, it's wide open and idle. My motor pulls around 19in/hg vacuum at idle....the 10psi spring really is ideal....but it makes the hooking/screeching sound even worse!

Thoughts?

 
Oct 24, 2016
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Couple things:

1: BOV spring is fine. I wouldn't change it.
2: Log indicates -to me- tune is aggressive, and will use throttle control as a means of trimming a bit more than we typically see thus you're making the BOV do work. If you put a stiffer spring in you'll make the activation rate go down but you're aggressive. I assume this was done to make the car more responsive and I'm sure it works. Not shy with the WGDC.

Bottom line is I'd keep the BOV spring and ditch the tune. I'm sure it's a powerful tune and feels good but IMO it's aggressive.
 

jareddlc

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May 1, 2021
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I'm also having this issue. Happened right after when i installed the 2nd set of mods. Shop told me it could be due to the silicon inlets. They also noticed the change of sound of my BOV.

I was running the following for 2 years without any sounds.
- VRSF 5in intercooler
- VRSF chargepipe
- BMS dual cone intakes
- Tial BOV with plain spring
- 1 year later replaced all my vacuum hoses with 3.5mm silicon ones

I then installed the following, and the noise began immediately
- Pure600 turbos
- VRSF Silicon inlets
- VRSF outlets
- VRSF catted downpipes

I then did a custom tune and the sound was still there. Today i changed my spring to black and it was wide open on idle. Drove around the block and the noise was still present, i reverted back to the plain spring. I had made a video a few days ago to post for some help, i'll leave it here as well.


first clip you can hear a "flutter" and second clip, the "hoot"

I'm not sure what to do at this point to get rid of that sound.