What type of bov is it and how is it vented?

You can't have all cylinders tdc and I'm not even sure why you are asking, but it's easy to set a screwdriver in the spark plug whole and stop when it's at tdc.

Do a search for boost leak test, there are hundreds of threads on it with pictures and all.

Wht kind of blow off valve do you have? Is it a knock off or a name brand?

Every bov I have ever owned fluttered at some point at low rpm/low boost. From Greddy Type S, HKS SSQV, and not my Tial does it. Some bov's flutter, others do not.

Also, do a boost leak test to about 15psi, and use soapy water and a squirt bottle to find them.

Turbo XS but runs off the stock inter cooler piping until I buy a Type S BOV for the chrome piping I have.

As for setting it at TDC I read on some site that the air can pass through the valves if not set at TDC and let air into the engine which would not let have a proper boost leak test.

With the last test I did was only through the turbo inlet and heard oil bubble in the engine which is when I did research and found that it should be in TDC so that all valves are closed.

Also this never had a BOV on it til I put this turbo on it, use to have the chrome piping with the standard metal bypass valve I believe is what you call it.

Kod said:

Well my BOV works as it should as long as I am at 5 lbs of boost, anything under it will flutter which I know is making the turbine spin backwards which this also happened with the old stock turbo that was on the car and it killed it.

Now this turbo is dieing and is on its last leg.

Usually when I start to hit 7 - 9 lbs of boost the needle is constantly shaking back and forth very fast.

But now it is starting to go to 10 - 11 lbs smoothly but def. is not pushing as it should and you can smell something burning.

Would my best bet be to upgrade to a 16g? or figure out how to set the car at TDC which I have never done and perform a proper boost leak test from the turbo inlet and Throttle body goose neck?

Also I should state that the original turbo that was on the car also did this.

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The turbo is spinning way to fast to make it spin backwards. You can't do it. It is just faster air running into slower air moving in reverse direction.

If you turbo were to spin backwards, it would force air back into the cylinders from the exhaust side. The amount of air for that to happen would have to be tremendous pressure. Far more than can be generated by the BOV not working.

Yea no possible ways it's spinning backwards. Even at idle the turbine is rotating pretty quickly and carrying momentum. The only thing I could see being an issue is if the bov is malfunctioning, the pressure rushes back towards the turbine when throttle is cut. this cause a loud squealing noise. But at low boost levels I don't see it being an issue. This was a common problem on the chrysler conquest being stock they had no bov. This was ok until boost levels go up and it damages the turbine.

what your experiencing is compressor surge, due to the BOV not opening when it should.

I'd bet you have a vacuum leak sir. Check your hoses and do a boost leak test.

I know everyone is telling you different things, so here's another one;

If this is happening during acceleration, while your accelerator is depressed what you're hearing is WASTE GATE FLUTTER, caused by your wastegate opening and closing very quickly in an attempt to regulate the boost.

Might be a boost leak somewhere, but that is NOT compressor surge, and is NOT your turbo spinning backward.

(Minor wastegate flutter is completely normal on most turbo vehicles under highload acceleration.)

PotatoFlakeSTi said:

If this is happening during acceleration, while your accelerator is depressed what you're hearing is WASTE GATE FLUTTER, caused by your wastegate opening and closing very quickly in an attempt to regulate the boost.

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How the hell would it be the wastegate if it's happening at 5psi and below, when the wastegate is never even CLOSE to opening?


O.P.- your BOV is killing your turbos. Sell that Turbo XS P.O.S. which has now cost you two turbos on eBay and pick up an uncrushed 1G valve, then watch your problems disappear.

thomcasey said:

The turbo is spinning way to fast to make it spin backwards. You can't do it. It is just faster air running into slower air moving in reverse direction.

If you turbo were to spin backwards, it would force air back into the cylinders from the exhaust side. The amount of air for that to happen would have to be tremendous pressure. Far more than can be generated by the BOV not working.

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He doesn't mean the airflow is physically turning the shaft the other direction- as it's been stated, the exhaust flow has much more energy and will never let this happen. He means the compressor airflow which cannot escape is backing up in the piping and loading the shaft the other direction, which has been proven to bend shafts and cause unnecessary bearing wear leading to premature turbo failure.

jusmx141 said:

How the hell would it be the wastegate if it's happening at 5psi and below, when the wastegate is never even CLOSE to opening?

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Because the BOV is failing below 5psi, and not above it?

That makes even less sense to me, the BOV is nothing more than a spring and piston.

He states that at 7-9psi his boost gauge needles "shakes"

Sounds like a wastegate problem to me.

PotatoFlakeSTi said:

Because the BOV is failing below 5psi, and not above it?

That makes even less sense to me, the BOV is nothing more than a spring and piston.

He states that at 7-9psi his boost gauge needles "shakes"

Sounds like a wastegate problem to me.

Click to expand...

Sounds to me like you don't know the first thing about a turbo system and you're just throwing out a couple of educated guesses.

You describe the BOV as nothing more than a spring and a piston- well what exactly is a wastegate in your eyes?

The needle is shaking at a boost level before the wastegate would even be signaled to open, it cannot be a wastegate issue.

If the wastegate diaphragm develops a hole, this will cause the wastegate to not open as it should, generating a much higher boost level than expected.

If a BOV diaphragm develops a hole, it will cause the wastegate to not open properly and not stay shut properly when boost is applied....which happens to be exactly what the O.P. is describing to be the problem.

I know how a turbo system works, but evidently am misunderstanding something in OP's description of the problem.

In both cases of failure too much boost is created.

I was under the impression that the wastegate is controlled by either a factory BCS, or an aftermarket option, which then allows enough pressure to open the wastegate.

The BOV is controlled by nothing other than positive pressure in the charge piping, and negative pressure in the intake manifold.

I'm happy to learn, maybe the use of "turbo flutter" is what is throwing me off.

"There is confusion in the automotive world about so called "wastegate chatter" or "turbo flutter". A noise created on lifting off the throttle in a turbocharged car, commonly described as a chipmunk or a rattlesnake, is often stated incorrectly as being a result of the turbo's wastegate closing.

The noise is in fact the air compressed by the turbo passing back through the compressor wheel of the turbo after the airflow is abruptly halted by the throttle plate closing, called compressor surge. However, in some cases, i.e. where the throttle plate doesn't open fast enough or is set up to only react to high boost, some chatter will remain. Surge can occur on diesels when the turbo is attempting to pressurize the air at a higher pressure ratio than the compressor wheel can flow at a given speed. Diesel engines have no use for a blow off valve as they do not have a throttle plate.

The chatter noise is very noticeable on World Rally Cars, where anti-lag is used.

A compressor stall like this can cause excess stress and wear on the turbo's shaft or bearings under higher load applications of the turbo (around 15 psi (1.00 bar) and greater depending on the trim and flow rate of the compressor side).

Actual wastegate flutter occurs instead under partial boost conditions such as partial throttle near the boost threshold. It sounds like FftFftFft not ShuShuShu and is caused by the rapid opening and closing of the wastegate at boost levels near the spring pressure. It is commonly heard more clearly and may be more prominent on cars with modified intake silencers, up-pipes, and or downpipes, and is not harmful."


If I'm completely off base, please let me know, as you have been... I love learning.

jusmx141 said:

Sounds to me like you don't know the first thing about a turbo system and you're just throwing out a couple of educated guesses.

You describe the BOV as nothing more than a spring and a piston- well what exactly is a wastegate in your eyes?

The needle is shaking at a boost level before the wastegate would even be signaled to open, it cannot be a wastegate issue.

If the wastegate diaphragm develops a hole, this will cause the wastegate to not open as it should, generating a much higher boost level than expected.

If a BOV diaphragm develops a hole, it will cause the wastegate to not open properly and not stay shut properly when boost is applied....which happens to be exactly what the O.P. is describing to be the problem.

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This is not a common trait on internal wastegates because they simply cannot reach quickly enough to cause the symptom of "flutter". Actually, I've never found any example like you've given that was curable through a wastegate modification....not that it isn't possible, it's just much more likely to be a blowoff valve issue.

Here's a few examples on another forum users who experienced the exact same issue after installing the same BOV. Coincidence?

TURBO XS RFL BOV compressor surge - SRT Forums -

http://www.wrxtuners.com/forums/f72/turboxs-bov-now-surge-26018/

http://www.wrxtuners.com/forums/f72/turboxs-bov-now-surge-26018/

I believe you, I just think it's hard to diagnose something like that without being physically near the car. And as my first post indicated, I was just adding another plausible explanation.

My 2011 STi has mild wastegate flutter, going uphill, 3500-4500rpm, 8-12psi, goes away by 15psi.


Also, your second link is about off-throttle, which is compressor surge.

jusmx141 said:

This is not a common trait on internal wastegates because they simply cannot reach quickly enough to cause the symptom of "flutter". Actually, I've never found any example like you've given that was curable through a wastegate modification....not that it isn't possible, it's just much more likely to be a blowoff valve issue.

Here's a few examples on another forum users who experienced the exact same issue after installing the same BOV. Coincidence?



TURBO XS RFL BOV compressor surge - SRT Forums -

turboxs bov and now surge - Subaru WRX Forum: WRX Forums

turboxs bov and now surge - Subaru WRX Forum: WRX Forums

Click to expand...

PotatoFlakeSTi said:

My 2011 STi has mild wastegate flutter, going uphill, 3500-4500rpm, 8-12psi, goes away by 15psi.

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I still don't see how it can be a result of the wastegate if it's happening before the wastegate is open. If the wastegate is open, your boost will be limited to the pressure it's at when it's open- end of discussion. It's not like it will open/close/open/close and then suddenly allow you to reach 15psi.

Your STi appears to be suffering from compressor surge, highlighted by the fact that you're going uphill when it happens. The increased load is not allowing the engine to rev but allowing the turbo to build more boost pressure than the engine can use at that particular RPM. Happens to diesels too- it can happen to any car, really.

jusmx141 said:

I still don't see how it can be a result of the wastegate if it's happening before the wastegate is open. If the wastegate is open, your boost will be limited to the pressure it's at when it's open- end of discussion. It's not like it will open/close/open/close and then suddenly allow you to reach 15psi.

Your STi appears to be suffering from compressor surge, highlighted by the fact that you're going uphill when it happens. The increased load is not allowing the engine to rev but allowing the turbo to build more boost pressure than the engine can use at that particular RPM. Happens to diesels too- it can happen to any car, really.

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Video of wastegate flutter (3k-4k rpm, and very common on boosted scoobies)
VF52 Turbo Flutter - YouTube

Video of compressor surge
Compressor Surge Demo - YouTube

I understand the other kind of surge, which is too much boost being created compared to what the turbo can generate off the current exhaust flow, which causes boost of fall slightly, which allows it to generate more.. So on and so forth, but I don't believe that to be what is occurring on my stock STi.

Oh.. Edit;

"The increased load is not allowing the engine to rev but allowing the turbo to build more boost pressure than the engine can use at that particular RPM"

NOOOPE, Check Testa. Boost is then controlled by the wastegate, thus creating wastegate flutter.

Well just so that you know before I even put a BOV on this car the original stock turbo in the car also did this with a standard by pass valve I got the BOV on it for the reason of it not always fluttering.

With the standard bypass it always fluttered even with the after I put this other stock turbo on it.

Last time I did a boost leak test the oil bubbled, so now should I just boost leak test from the throttle body elbow and see whats leaking from their? Since every time I do it from the turbo inlet it just leaks into the oil.

1) Regardless of these theories, you need to perform a boost leak and vacuum leak test on your car. I will bet you have a vacuum leak. You know that vacuum line running to your bov? That is what dictates the behavior of your bov. As your throttle plate closes, the air pressure in your intake manifold changes. That change in pressure is carried to your bov through that vacuum hose allowing the bov to open as the compressed charge air returns in the opposite direction through your intercooler piping. This in turns by-passes the turbo and SHOULD recirculate it back into the intake. This is a very common issue with older turbo cars. Vacuum lines crack and get brittle causing small leaks. Get a pack of silicone vacuum hoses and replace them all is my opinion.

2) By-pass valve, diverter valve, blow-off valve...these all refer to the same basic thing. A device that diverts pressurized air away from a particular source. In this case, it's preventing it from getting back to your turbo at the compressor outlet.

PotatoFlakeSTi said:

Video of wastegate flutter (3k-4k rpm, and very common on boosted scoobies)

Video of compressor surge

Click to expand...

Those are two great videos of compressor surge you have there- one occurring under load, and one occurring when the throttle is cut either because the BOV spring is too stiff or there is no BOV at all.

PotatoFlakeSTi said:

NOOOPE, Check Testa. Boost is electronically limited, the wastegate opens to relieve boost. Car wasn't made in 1940.

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What the HELL are you talking about? I'm so done with this discussion.