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Thread: A long chirp or whistle under boost

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    A long chirp or whistle under boost

    If I lay into it in 3rd or 4th, along with the normal turbo sound, there is a noise that happens twice during the gear run. The sound is not high volume, has a soft start and end, and seem to happen after spool up and right before peak boost. Is this the waste-gate making the noise under certain conditions? A note that this doesn't really happen in ambient temps above 80* but can replicate in temps between 40* and 65*. Etune done 73* at sea level. This noise is recent though. Since 1-9-19.
    This is a 2018 WRX with Cobb FF kit and etune. Everything else being stock. Under 17000 miles. Just changed the oil and no glitter. No CEL's or issues, just this new noise and concern. Anyone been down this road?


  2. Top Of Page | #2
    On a quest of STi erudition! Alin's Avatar

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    Re: A long chirp or whistle under boost

    @dden4012

    Alight, we need to clear up a few things first:

    1) is your car properly warmed up (coolant and oil temps) BEFORE you go WOT in 3rd and 4th gears?
    2) are you going WOT above 3,000 RPM?
    3) is this the kit that you have? https://www.cobbtuning.com/products/...-sti-2015-2018
    4) where is the noise coming from?

    I was going to mention that an aftermarket BPV could cause a sound like that. (Happened to me in the past.) However, that kit doesn't mention a BPV, so I'm assuming yours is stock. I don't know if a turbo inlet could affect that, but I'm leaning more towards no. I just thought about question 4 just now. Does the sound come from the rear of the car or the front of the car? It could be be the fuel pump if from the rear. Based on your description, if the noise begins right after spool up and ends right before peak boost, any number of things could be the culprit. We need a bit more information. The kit doesn't mention an EBCS either, so I'm assuming that's stock as well.

    Guys, do you have any ideas? Assuming stock BPV and stock EBCS, and with a bit more information from the OP, we should be able to determine what's making the sound!
    @HolyCrapItsFast @Batmobile_Engage @Boogieman98 @Raven32 @Grinder34 @IGOTASTi @Doppelganger @black bandit


    Quote Originally Posted by Batmobile_Engage View Post
    It doesn't have to have a nut on the outside. Many are short, but I often try to find long ones that sometimes have a bend in them.

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  4. Top Of Page | #3

    Re: A long chirp or whistle under boost

    Front driver side (j pipe side) best I can tell.
    Yes @ running temps. Fully warmed up
    The FF kit is just a sensor basically (WRX not STI).
    https://www.cobbtuning.com/products/...-wrx-2015-2019
    Yes above 3k.

    This is not the same car but the tone and type of sound is similar. Mine is not nearly as loud or persistent. Just couldnt find a better example.


  5. Top Of Page | #4
    On a quest of STi erudition! Alin's Avatar

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    Re: A long chirp or whistle under boost

    Ah, alright. So, you have an FA20DIT then. I misread your original post. Well, I don't know shit about the new platform, but I do know the turbos are not from the IHI VF series. Well, your car does have 8 injectors and this does change parameters. So, now a few more questions...

    1) did this noise occur before you installed the FF sensor kit?
    2) what fuel are you currently running right now and how long have you been running it for?

    I'd imagine @HolyCrapItsFast has the answer to this.

    This has to do something with fueling then, right?

    "COBB has performed internal testing in multiple geographic locations with different fuel sources in addition to compiling data from COBB retail shops, our Protuner network, and customers. Results varied significantly. Some users ran several tanks of E85 in a row without issue while some experienced serious loss of fuel pressure in as little as 1-2 tanks of fuel.We suggest monitoring fuel pressure for oscillations. After having fuel pressure issues, some users were able to flush the HPFP (high pressure fuel pump) out with low ethanol gasoline and get it to operate normally again, while others had to replace the whole pump assembly before they could safely drive the car again. After replacing the pump some users experienced repeat failures if they continued to run E85 fuel."


    Quote Originally Posted by Batmobile_Engage View Post
    It doesn't have to have a nut on the outside. Many are short, but I often try to find long ones that sometimes have a bend in them.

  6. Top Of Page | #5
    Eats rice, drinks V8. Batmobile_Engage's Avatar

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    Re: A long chirp or whistle under boost

    Quote Originally Posted by dden4012 View Post
    Front driver side (j pipe side) best I can tell.
    Yes @ running temps. Fully warmed up
    The FF kit is just a sensor basically (WRX not STI).
    https://www.cobbtuning.com/products/...-wrx-2015-2019
    Yes above 3k.

    This is not the same car but the tone and type of sound is similar. Mine is not nearly as loud or persistent. Just couldnt find a better example.
    One thing you can try is this. At ~45 mph in 4th, put your foot down (but not quite WOT). Do you hear the noise?
    Then, at ~75 mph in 4th, put your foot down (but not quite WOT). Do you hear the noise?

    If YES and NO, then I would suspect compressor surge. In which case, nothing is likely to be wrong mechanically, but rather you are putting too much load on the engine for the rpm level.

    One other thought is that it could be your intake. I kind of doubt this, but I used to be able to induce a whistle at the right throttle position in my NA Integra back in the day, due to my aftermarket SR Intake.

    My expertise is with the GD chassis STi, so I need all the info on mods and such as possible, in order to come up with a better theory.

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  7. Top Of Page | #6

    Re: A long chirp or whistle under boost

    Quote Originally Posted by Batmobile_Engage View Post
    One thing you can try is this. At ~45 mph in 4th, put your foot down (but not quite WOT). Do you hear the noise?
    Then, at ~75 mph in 4th, put your foot down (but not quite WOT). Do you hear the noise?

    If YES and NO, then I would suspect compressor surge. In which case, nothing is likely to be wrong mechanically, but rather you are putting too much load on the engine for the rpm level.

    One other thought is that it could be your intake. I kind of doubt this, but I used to be able to induce a whistle at the right throttle position in my NA Integra back in the day, due to my aftermarket SR Intake.

    My expertise is with the GD chassis STi, so I need all the info on mods and such as possible, in order to come up with a better theory.
    Yes from a 45mph roll on in 4th gear but only one instance of the sound with a "not quite WOT" input, so there is a threshold that has to be reached to hear it twice.
    Maybe from 75mph in 4th, but the onset of good boost is much faster, spending less time in the whistle zone conditions.

    I would be suspecting a boost leak by the drivers side of the intercooler but I'm still hung up about the influence of cooler outside temperature. In 80* + temps i never heard this whistle noise. But i should double check this because I really don't want to have to talk the tuner into doing anything yet, he is suspecting a mechanical issue. I would much rather fix a minor boost leak. But the temperature is the only variable that has changed since the e tune.
    Since it only happens when the outside temp drops, I think it has something to do with temp comps in the tune. Fuel pressure, LT and ST trims, look good, hits boost no problem. No obvious issues just this new temperature biased noise.


  8. Top Of Page | #7
    Eats rice, drinks V8. Batmobile_Engage's Avatar

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    Re: A long chirp or whistle under boost

    Do you have a Cobb AP or some other means of data logging? A boost leak could be noticeable in a log, as well as a handful of other potential issues. I still have a slight suspicion that you are hearing some compressor surge...nothing damaging per se, just something that is pretty common with the factory turbo due to it's small size. At heavy throttle input at lower rpms, the turbo is producing more flow than the engine can consume. So pressure waves are reflected back into the compressor which can cause that noise. Not saying I'm 100% sure that is the issue though...just a theory.

    Do you have a boost gauge you can monitor?

    Last edited by Batmobile_Engage; 4 Weeks Ago at 10:51 AM.
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  9. Top Of Page | #8
    Eats rice, drinks V8. Batmobile_Engage's Avatar

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    Re: A long chirp or whistle under boost

    Compressor Surge examples...





    Sometimes the "sh-sh-sh-sh-sh" sound can take on more of a high-pitched tone due to other factors such as an aftermarket intake.

    (I apologize if you are already aware of all this. I can never be sure what knowledge level we're all at, here on the forums.)

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  11. Top Of Page | #9

    Re: A long chirp or whistle under boost


    This is my clip. Got three chirps now. Stock intake and filter.


  12. Top Of Page | #10
    Eats rice, drinks V8. Batmobile_Engage's Avatar

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    Re: A long chirp or whistle under boost

    From the video, the sound seems to be completely different than what I expected. Am I right in saying it sounds a little like blowing over the neck of a glass bottle? It almost sounds like a high-frequency, metal-on-metal vibration that is reverberating into the cabin. It reminds me a little bit of when I had a turbo go bad years ago. But it sounds even more like a slightly loose heat shield or like my aluminum skid plate, when my header used to vibrate against it at certain rpms/engine loads.

    I'm very hesistant to suggest turbo bearing failure, car sounds are just so hard to diagnose on the internet.

    Is this your first turbocharged car?

    Last edited by Batmobile_Engage; 4 Weeks Ago at 09:35 AM.
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