BOV flutter vs. compressor surger

[madman]

I found a couple threads where this was mentioned but never a specific answer.

Is there a difference?

I've felt compressor surge before and the whole car sputters and shakes but when I hear a fluttering noise after I let off the throttle on a light acceleration is that my Tial BOV and not the compressor? The car does not buck or hesitate when this happens which make me think there is just not enough pressure or vaccum to fully open the valve on the Tial and the valve just bounces or flutters while the air is releasing.

Sometimes it just flutters a couple seconds and somethimes it flutters briefly and then releases.

 

[MyBeatGSX]

The car doesn't usually buck or hesitate because of compressor surge. Most BOV flutter is compressor surge, people have just inaccurate called it "BOV flutter". Last time I checked, Tials don't make fluttery noises.

 

[99gst_racer]

They are completely different.

Definition: Compressor Surge: A disturbance occurring in gas compressors, especially centrifugal compressors, due to excessive pressure across the compressor in which the compressor blades stall and air flow suddenly drops. The flow can fluctuate and the compressor be damaged. It is the point of instability at which a compressor surges across, trying to reestablish its point of stability.


Are you sure your BOV isn't set too loose?

And I thought you fixed this problem years ago?

I have experienced both before, and my personal rule of thumb is usually this. If you can only hear it's it's probably BOV flutter. It's it's audible and you can feel it, then you're probably experiencing compressor surge.

 

[MyBeatGSX]

Feeling it isn't always (read: rarely) accurate. I've experienced true WOT surge and felt nothing. The boost gauge was going crazy, but the car continued to accelerate with reasonable smoothness. Someone that's isn't 100% in touch with how the car should feel won't even noticed it, especially if its throttle lift surge.

 

[madman]

Well I had most of the issues fixed, mainly installing the o-ring on the Tial and then lately I started to develope a pesky vaccum leak.

Then the BOV started to flutter more often and at heavier throttle lifts. I figured this was due to the low vaccum pressure. I think we got most of the leak fixed and the Tial releases like it used to but I still get that low throttle lift flutter. I'm thinking that the spring is still a little too stiff and that I need to get softer spring, something I never switched out.

So I just wanted to ask about the difference. If it's just the BOV then I can wait a little before I get a new spring. If it's all compressor surge then I need to make sacrifices and get the spring and replace it. I heard they were quite expensive but I guess I need to make some phone calls. Plus time is a big issue for me right now.

 

[madman]

Feeling it isn't always (read: rarely) accurate. I've experienced true WOT surge and felt nothing. The boost gauge was going crazy, but the car continued to accelerate with reasonable smoothness. Someone that's isn't 100% in touch with how the car should feel won't even noticed it, especially if its throttle lift surge.

I never noticed my gauge go crazy but I'll keep a better eye on it. I'm using the Greddy Profec as my gauge, digital, would I be able to see the change in PSI, going crazy like you mention as I would on a mechanical guage?

 

[MyBeatGSX]

You won't see it, I was refering to the other kind of surge at WOT. When the turbo is flowing more CFM then the engine can take in at a given pressure.

Try neutral reving it (you don't have to boost, just a quick vac change) and see if the BOV pops open. If its popping open under the vacuum spike, then the spring is fine and you're just hearing BOV noise. When I had a broken RS that wasn't opening at all, the surge noise was very obvious, it sounds nothing like "BOV flutter". If you can imagine a loud ocilating (sp?) bird chirp, something like that. BOV flutter has more of poppy, vent noise and less of a chirp.

 

[99gst_racer]

If you still have a vacuum leak, there's a good chance the BOV of not opening far enough or when it should, and you are experiencing a minor case of compressor surge. Are you 100% sure you fixed all vacuum leaks?

 

[madman]

If you still have a vacuum leak, there's a good chance the BOV of not opening far enough or when it should, and you are experiencing a minor case of compressor surge. Are you 100% sure you fixed all vacuum leaks?

No and that's after $350 at the shop.

Turns out the my EGR block off plate was leaking and supposedly they put on a new IM gasket.

They said they measured my vacuum right around 20(not sure the units of measure) off the IM, although my boost gauge is only showing -7psi which is 14xx which is low. So either I still have a big leak, my guage is going bad or a leak in the hose going to the gauge.

Oh ya, another symptom of my bad leak, the car was loping real bad at idle. Sometimes it wanted to die. My gauge was reading -5 to -6 psi. After they did what they did it idles a lot smoother but like I said above my guage doesn't show good vacuum.

I sprayed carb cleaner everywhere to find a leak no luck. As far as doing a pressure test I haven't had any time.

 

[madman]

You won't see it, I was refering to the other kind of surge at WOT. When the turbo is flowing more CFM then the engine can take in at a given pressure.

Try neutral reving it (you don't have to boost, just a quick vac change) and see if the BOV pops open. If its popping open under the vacuum spike, then the spring is fine and you're just hearing BOV noise. When I had a broken RS that wasn't opening at all, the surge noise was very obvious, it sounds nothing like "BOV flutter". If you can imagine a loud ocilating (sp?) bird chirp, something like that. BOV flutter has more of poppy, vent noise and less of a chirp.

My flutter sounds like a muffled machine gun.

Doing the neutral rev test is what started my old thread. I couldn't get the Tial to release after a neutral rev, not like my old Greddy type-S. I would almost have to red line it to get any release from the Tial and even then it was very weak. Thats what made us think the spring was too stiff. During driving it was flutter several times then release. Very funny sounding

Then I realized the Tial didn't come with the o-ring, or I lost it, either way I put on an o-ring which brings me to now

 

[madman]

I think tomarrow I'm going to do my own vacuum test at the IM and see what it reads.

 

[MyBeatGSX]

My flutter sounds like a muffled machine gun.

Deep, low pitched noise = definately surge.

 

[CanadianTSi]

Compresser Surge will happpen on spool-up and it will be a fairly violent bucking. I used to suffer from compressor surge on my 50 trim Until I slowed the spool abit.

Sounds to me like your BOV is just fluttering a little.

 

[ivanr4g63]

In wich case, you need to address to the BOV vacuum line, a very common mistake is to run the MBC off the same vacuum line, if so you need to run a straight vacuum line from the intake manifold to BOV and find another boost source for the MBC (preferrably from the J-pipe).

You see when sharing the BOV vacuum line you could be substracting vacuum pressure that in turn could hurt your BOV ability to fully open making it to flutter, I had this issue with my HKS SSQV.

 

[madman]

In wich case, you need to address to the BOV vacuum line, a very common mistake is to run the MBC off the same vacuum line, if so you need to run a straight vacuum line from the intake manifold to BOV and find another boost source for the MBC (preferrably from the J-pipe).

You see when sharing the BOV vacuum line you could be substracting vacuum pressure that in turn could hurt your BOV ability to fully open making it to flutter, I had this issue with my HKS SSQV.

Funny enough I used to have the MBC t'd off the BOV line and the vacuum was good. Then when I installed the o-ring to the BOV I decide to run a straight line from the IM to the BOV and run the MBC of the compressor housing of the turbo. That's when I started having vacuum issues. Weird

 

[ivanr4g63]

That is really weird... in my case It all work'd out perfect, I still have a bit of BOV flutter but only when i let of the gas easy and built a few PSI of boost but otherwise it works good, matter of fact running a straight vacuum to the BOV made it a louder.
are you sure all your vacuums that go to the MBC are nice and tight?