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Thread: Antisurge/Ported Shrouds

  1. #1
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    Default Antisurge/Ported Shrouds

    In order to understand how an 'anti-surge' compressor housing works (which is technically a 'ported shroud'), you need understand what surge is, in the first place.

    Surge: The 'Surge Line' is the leftmost boundary of a compressor map. This is where flow instability occurs - This is where the compressor wheel is spinning at a high enough speed to force more air than the engine can injest. On initial thought, one might think this would just give you more pressure in the intake - and this is true, as long as you are on the compressor map. Basically, the surge line is the MINIMUM airflow needed to keep the pressure from backing up, and causing reverse flow pressure waves - these are INCREDIBLY damaging to the turbocharger!

    Follow that thought a little further - when are you constantly seeing high flow of air, but little entering the intake? That's right, when you get off the throttle from boosting. This surging is what a BOV protects the turbo from. You also see this, if you have attempt to spin a compressor wheel such that it is forcing more air into the intake than the engine can take - or attempting to get more boost per rpm of the compressor wheel, than it is designed for.

    That said, the ported shroud allows the surge line to be moved further left - this is because the compressor housing allows some of the air that starts to get backed up in the intake, to flow back out the housing.

    Here's a pic from Garrett:

  2. #2
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    Default Re: Antisurge/Ported Shrouds

    I know im bringing this back from the dead, but at what point anti surge port be used?
    reason im asking is that my turbo has an anti surge compressor housing, but i chose to leave the port closed for the time being.
    thanks
    -pete


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  3. #3
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    Default Re: Antisurge/Ported Shrouds

    If you have it, use it - that's my thought on it

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    Default Re: Antisurge/Ported Shrouds

    I'm not sure I understand. Doesn't this increase the time it takes to build boost?

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    Default Re: Antisurge/Ported Shrouds

    I've never definitively found an answer to that question, Grim. I see no reason why it would, though.

  6. #6
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    Default Re: Antisurge/Ported Shrouds

    All reports I read before buying my 04z was it does add to spool time, I specced mine with a normal Comp cover and it surged like a bitch at low throttle opening/closing as the BoV springs were too heavy to allow them to respond fast enough.

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    Default Re: Antisurge/Ported Shrouds

    Ian, did you ever run it with a ported afterword? I've always 'heard' that it adds to spool time, but I've never seen it verified, anywhere.

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    Default Re: Antisurge/Ported Shrouds

    Seems logical to me. It's essentially adding a 'leak' to the pressurized portion of the intake tract, right?

  9. #9
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    Default Re: Antisurge/Ported Shrouds

    Ported shroud is to stop this: http://videos.streetfire.net/video/T...sor_163406.htm

    True compressor surge has nothing to do with a BOV...
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    Default Re: Antisurge/Ported Shrouds

    Quote Originally Posted by GrimJack View Post
    Seems logical to me. It's essentially adding a 'leak' to the pressurized portion of the intake tract, right?
    Watch Poodles' video - that's what real compressor surge is - when you are attempting to flow LESS air than the compressor is capable of delivering.

    The ported shroud allows that airflow to circle back into the tract, preventing surge.

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