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BOV Flutter/Surge Clarification Help

Posted by spadepro22, Oct 2, 2012

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  1. spadepro22

    spadepro22 Proven Member

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    Let me start off by saying I've researched, but still have some questions that I'm not sure about. 1st off I've read that bigger compressor wheels with a smaller turbine will cause compressor surge. I have a 20g compressor wheel with 16g turbine in a down firing housing. Could I still get compressor surge?

    Next, I installed a new NGR bov and its fluttering under low boost but fine in the higher range. I've read that for the valve to hold high boost it might cause some surge/flutter down low. Some say that its fine and others say you shouldn't have any. Is there any clarification here? I haven't adjusted my bov softer from the factory setting yet, because I don't want it to leak. I'm running 18psi so if I did the single spring mod, do you think it would hold the 18-20 psi, or should I just adjust it softer to see if the flutter/surge stops without leaking?

    Any videos with flutter and surge would also help being I can't seem to tell them apart at this point
     

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    1993 Eagle Talon TSi AWD
    · 1G DSM
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  2. ramsack

    ramsack Proven Member

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    Surge is while making boost and has to do with the compressor and turbine mismatch that you mentioned, not letting off the throttle. Flutter when lifting the gas and opening the BOV is harmless.
     
  3. spadepro22

    spadepro22 Proven Member

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    So your saying surge happens in throttle, and flutter is ok? If that is correct I don't think I have surge and shouldn't worry about the flutter? Some say the flutter is also bad.
     

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    1993 Eagle Talon TSi AWD
    · 1G DSM
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  4. ramsack

    ramsack Proven Member

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    Flutter happens when the BOV opens, pressure in the charge pipe drops enough so that the BOV closes, the pressure starts rising again because the turbo is still spinning, then BOV opens, and the process loops. It does NOT force air back across the compressor, which is what surge is. Surge is also placed apart from flutter because surge happens when the turbine is being driven. The only force driving flutter is interia. The mass of the moving parts of a turbo is not enough to cause damage to itself from just building boost. If people can't grasp how feedback loops work, they shouldn't be tinkering with cars (the people who are adamant about flutter being bad, not you, OP).
     
  5. spadepro22

    spadepro22 Proven Member

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    Made me feel bad at the end of post:( til I got to the end. Well happy to know I don't have a surge issue. It seems like you pretty much cleared the flutter issue too, unless someone wants to disagree.:thumb: I still would like to see a video with surge to know what it sounds like if theres a good link out there.(I've seen some on youtube but not a good 1)
     

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    1993 Eagle Talon TSi AWD
    · 1G DSM
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  6. ramsack

    ramsack Proven Member

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    I'm sure disagreements will follow at some point :)
     
  7. WES_393

    WES_393 DSM Wiseman

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    True compressor surge.
    True Compressor Surge - YouTube

    Some pretty dramatic flutter shown here, which is typically referred to as compressor surge.
    sxmuch with flutter - YouTube

    True compressor surge is definitely very bad. But whether turbo flutter is actually harmful has always been a topic for debate. However, most can agree that some light turbo flutter isn't a big deal.
     
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  8. spadepro22

    spadepro22 Proven Member

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    I'm feeling better already about the situation being my turbo was recently rebuilt.:)
     

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  9. ramsack

    ramsack Proven Member

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    Compressor surge is the breakdown in the ability of the compressor to maintain pressure. Air starts flowing backwards across the compressor and mainly bends the blades. It's cavitation. Boat propellers can do the same thing, but it's visually noticeable because gas just instantly appears out of water. It creates shock waves and can destroy props, as well.

    Flutter just needs to stop being called surge. It's an insult to people in aeronautics (I may not design airplanes and space ships, but I can understand compressor surge/stall). It's a simple feedback loop. It's no different than an ECU injecting some fuel, waiting for the firing stroke, waiting for the exhaust stroke, waiting for that batch of exhaust to reach the O2 sensor, waiting for the O2 sensor to react, and waiting for the ECU to calculate the new values from the feedback from the O2 sensor. The difference is the speed in which that happens. Electrical signals are fast. Air and mechanical parts are extremely slow.
     
  10. spadepro22

    spadepro22 Proven Member

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    This is some good info. Thanks man
     

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