Fluttering/chopping noise while spooling

[AWDYEAH]

Hey all! So I started to notice this strange noise after coming back from the tail of the dragon late summer. It happens under partial throttle when the car is loaded (normally on a small incline). Mods are ECS intake and FMIC, resonator delete, and 034 Stage 1 (currently on 93 since the dragon).

My first suspicion was the diverter valve. I removed it, oiled it up and popped it back in. I didn’t notice any noise after that but I didn’t have a lot of time to drive it that night. A week later I took the car out today and noticed the noise again with the windows down. Seems to be more noticeable in S mode vs D, but can be heard in both.

This video sounds pretty much exactly what I’m hearing. Any thoughts?

https://youtube.com/shorts/D1reUaMGuf8?feature=share

Thanks in advance


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[Speedster00]

Mine does it some too. Especially on a Dyno. I've been told it's normal.

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[AWDYEAH]

Mine does it some too. Especially on a Dyno. I've been told it's normal.

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That makes me feel a little better, thanks!


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[Requiescat]

That would be the sound of your exhaust exiting via the wastegate. It opens to allow excess exhaust to go out the downpipe so that you only spin the turbo as fast as you intend to.

[AWDYEAH]

That would be the sound of your exhaust exiting via the wastegate. It opens to allow excess exhaust to go out the downpipe so that you only spin the turbo as fast as you intend to.

Thanks, I’ve had quite a few turbo cars that were modified and I’ve not heard this particular noise before. Do you know why it just started to become noticeable? I went down a rabbit hole on Google and I did read a couple of posts that mentioned what you said. I appreciate the reply! I was thinking for a hot second I’d somehow damaged the fins.


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[brandonbanana]

Hey all! So I started to notice this strange noise after coming back from the tail of the dragon late summer. It happens under partial throttle when the car is loaded (normally on a small incline). Mods are ECS intake and FMIC, resonator delete, and 034 Stage 1 (currently on 93 since the dragon).

My first suspicion was the diverter valve. I removed it, oiled it up and popped it back in. I didn’t notice any noise after that but I didn’t have a lot of time to drive it that night. A week later I took the car out today and noticed the noise again with the windows down. Seems to be more noticeable in S mode vs D, but can be heard in both.

This video sounds pretty much exactly what I’m hearing. Any thoughts?

https://youtube.com/shorts/D1reUaMGuf8?feature=share

Thanks in advance


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Totally normal especially when adding load. I experience this especially when on a higher gear under heavy load. This was on my B9 S4 on JB4 tune.

[Jetta03]

It's not normal. That sound is turbo flutter/compressor surge and if you let it go long enough it will eventually damage the turbo fins/bearings.
Your divertor valve is there expressly to prevent this.

[Sturn992]

I have had that on v2.1 of 034 stage 1 I have not noticed it since v2.1 but we will see if it returns. I suspect it is compressor surge like stated above

[Requiescat]

It's not normal. That sound is turbo flutter/compressor surge and if you let it go long enough it will eventually damage the turbo fins/bearings.
Your divertor valve is there expressly to prevent this.

This is incorrect. It is not compressor surge as it's while under load (aka in boost) and not the diverter valve would be opening to release pressure. It's called Wastegate Flutter.

Also, compressor surge does not damage turbo fins or bearings this has been disproven many many times.

[carterferguson]

This is incorrect. It is not compressor surge as it's while under load (aka in boost) and not the diverter valve would be opening to release pressure. It's called Wastegate Flutter.

Also, compressor surge does not damage turbo fins or bearings this has been disproven many many times.

THIS is incorrect. It is absolutely compressor surge. Compressor surge is caused by the turbo flowing more air at a given pressure than the engine can flow at that pressure causing the compressor blades to “chop” the already compressed air in the charge pipe. Very typical with small quick spooling turbos. If you force them to spool before the engine can really move some air you get surge like this while in boost.
You shouldn’t be able to hear an internal gate “flutter” unless you’re referring to wastegate rattle which these turbos are not susceptible to since their wastegate valves are solid.
Diverter valves only open when either pressure has exceeded spec by more than the allowed threshold as a last resort safety net or when the setpoint drops drastically (when you get off the accelerator) to evacuate the pressure that just hit a closed throttle plate.


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[Rob01S4]

Ya sorry requiestcat that’s not correct. You can absolutely have compressor surge happens under boost and at high load it’s the most dangerous. It most certainly can damage turbos and in turn your motor. But like you said, What happens is soemtimes people confuse BOV/DV flutter for surge when it’s just that not a lot of air is being bypassed.

I cannot say if OPs issue is surge.. would kinda have to see it happening.. and much easier if on a dyno. But if it’s happening just like in the video - that is compressor surge.

[Sturn992]

Sorry for my typo V2.2. I have attempted to recreate the sound but with 2.2 I have not been able to

[AWDYEAH]

I’ll have to plug in my laptop and see what version I’m running but I believe it to be the latest version of the Stage 1 tune.

It sounds like I need to get ahead of this issue and try to pinpoint where the issue is coming from.


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[Speedster00]

Maybe Im missing a specific sound, but my car flutters under load. I was told by a few people and tuners that its normal and very evident on tuned cars. I understand the theory behind improper compression, if thats what youre actually hearing. Heres a video of my car on the dyno. Flutter about 3K RPM is apparent.

https://youtube.com/shorts/MRZWFxviZZE?feature=share

[AWDYEAH]

Maybe Im missing a specific sound, but my car flutters under load. I was told by a few people and tuners that its normal and very evident on tuned cars. I understand the theory behind improper compression, if thats what youre actually hearing. Heres a video of my car on the dyno. Flutter about 3K RPM is apparent.

https://youtube.com/shorts/MRZWFxviZZE?feature=share

That’s exactly what I’m hearing!


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[Speedster00]

That’s exactly what I’m hearing!


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from what Ive read and heard, the stock turbo is very good at making power down low. unlike a TTE. So the factory turbo spools faster than the motor RPM wants to use it, and that flutter is the dump valve releasing(burping) pressure until the motor RPM comes up and wants to use the boost, thus the flutter stops about 35-3700 RPM. Again, Ive been told this is normal but there are some tuner guys on here more knowledgeable than me for sure.

[SHCKR]

Maybe Im missing a specific sound, but my car flutters under load. I was told by a few people and tuners that its normal and very evident on tuned cars. I understand the theory behind improper compression, if thats what youre actually hearing. Heres a video of my car on the dyno. Flutter about 3K RPM is apparent.

https://youtube.com/shorts/MRZWFxviZZE?feature=share

I was getting a lot of this with the carbnlab intake

[Jetta03]

Here's a quick video on replacing the diverter valve which describes I think exactly the issue you are seeing in detail......
https://www.youtube.com/watch?v=bM29MoZl25U

[Speedster00]

Here's a quick video on replacing the diverter valve which describes I think exactly the issue you are seeing in detail......
https://www.youtube.com/watch?v=bM29MoZl25U

right, Ive seen that. He has a failed valve for sure . The valve should only make certain sounds. not burble non stop like his is in the video.

[Requiescat]

Here's a quick video on replacing the diverter valve which describes I think exactly the issue you are seeing in detail......
https://www.youtube.com/watch?v=bM29MoZl25U

No, that is not at all what OP is experiencing. Not even in the slightest. That's turbo flutter (you can call it compressor surge) and happens off throttle. You would not hear that noise under load. (To be clear, that is definitely a failed valve and is not supposed to make that noise, but again that is not what is happening to OPs car)

The diverter valve does not open under load to regulate pressure. It opens when you are off throttle to release the pressure in the charge pipes.

The wastegate opens to regulate pressure while under load. The turbulant exhaust flow that is split between the wastegate opening and the turbine outlet is what causes the noise. It amazes me that no one here understands this.

The subaru in this video has an external wastegate: https://www.youtube.com/watch?v=b0HZdZUOatg You'll hear the exact sound that OP is hearing, just louder.

Now can anyone guess why you'd hear the sound more on an incline or on a dyno? Because you're loading the engine more than the turbo requests and as a result the wastegate opens to not cause an overboost condition.