Possible Boost Leak? or is it in my mind?
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This is a discussion on Possible Boost Leak? or is it in my mind? within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; I am new to turbo cars so I don't really know what to expect but I have been reading loads ...

  1. #1
    Registered User hindude's Avatar
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    Possible Boost Leak? or is it in my mind?

    I am new to turbo cars so I don't really know what to expect but I have been reading loads on forums. I have a 2012 WRX with ~9k miles. It is stock except for an AccessPORT Stage 1 OTS map tune. The map says "Boost Targets: ~16.5psi peak boost pressure tapering down to ~13.5psi by the 7000 RPM redline, +/- 0.8psi."

    I did some data logging and I'm not sure what the taper is supposed to look like but after mine spikes to 16.3 I always get a drop to 14.xx and then boost builds back up to 15.xx. Is this normal behavior? It is the drop that concerns me. I feel like there may be a small boost leak somewhere. I searched to see if I could find an answer to this or even boost graph I could look at for a stage 1 WRX but no luck.

    Here is a graph of my Boost (psi) vs. RPM from the data log I did with the AP. Time intervals are at 0.3 seconds. I did this pull in 4th gear.



    Am I just being paranoid or is there really a problem here? I called up Subaru and the service center said that the car would throw a CEL if there was a leak. I was hoping they could just pressurize the intake and see if it is holding pressure, but they want to drive the car around to run some kind of "test". I'd rather not bring my car in to have some mechanic joy riding in it.

    Thanks for any help you can provide.
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    Master Baiter EJ257's Avatar
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    Start your log earlier. Start in 3rd @ 2K RPMs
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    Moderator Donkey's Avatar
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    If it was a boost leak it would not act like that. It would never go back up. It's just the factory boost control system doing it's thing on a generic map.
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    Registered User hindude's Avatar
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    Thanks for the input. I'll grab a 3rd gear pull on my way home from work.
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    Registered User hindude's Avatar
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    Here is a 3rd gear pull on the Cobb OTS Stage 1 93 octane map. This didn't show the same behavior of spiking, dropping and rebuilding as the pull in 4th did, but it barely hit 16psi too. (target is 16.5 +/- .8)

    Would this warrant changing to the higher waste gate map or is this a sign of a slight boost leak?

    NOTE: I'm not sure if this would affect it, but I was going *slightly* up hill when I captured this log (was the only spot on my commute home where I could slow down and punch it.) If this would skew the data, I'll try to capture a pull on a more level road.

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    Moderator Donkey's Avatar
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    It is not a boost leak. You do not need the HWG map. It is supposed to taper down like that. You even posted the info from Cobb's map notes in your first post:

    Boost Targets: ~16.5psi peak boost pressure tapering down to ~13.5psi by the 7000 RPM redline, +/- 0.8psi."

    The car will always have more trouble controling boost in 4th and 5th gear since the WGDC is a somewhat global table that does not have per gear compensation.
    Last edited by Donkey; 03-14-2013 at 05:36 AM.
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    Registered User EndlessSea's Avatar
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    If you had a boost leak. It wouldn't be holding boost. Way back n the day My bov on my 240sx leaked pretty bad. I normally held about 14.5 psi in the midrange and 11 at redline. Then It started leaking it would flutter around 7-9 psi at most. And ran pig rich to boot. So I don't think that's your problem.

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    Quote Originally Posted by Donkey View Post
    The car will always have more trouble controling boost in 4th and 5th gear since the WGDC is a somewhat global table that does not have per gear compensation.
    This is important. Adjusting WGDC and Turbodynamics for optimized spool in 3rd gear may lead to boost spiking and unstable control in 5th gear at WOT. The key here is to find the happy medium. You'll sacrifice a little spool in 1-3 gears for stable BC in the top gears. This is the physics behind a bleed-type and interrupt-type EBCS system.
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    zax
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    Quote Originally Posted by EndlessSea View Post
    If you had a boost leak. It wouldn't be holding boost. Way back n the day My bov on my 240sx leaked pretty bad. I normally held about 14.5 psi in the midrange and 11 at redline. Then It started leaking it would flutter around 7-9 psi at most. And ran pig rich to boot. So I don't think that's your problem.
    Not necessarily. You can't make that judgement! Your EBCS will target the boost according your BC tables. If the car has a boost leak, the car will simply try harder to hit target boost, unless the leak is so very bad that the turbo is run far out of its efficiency range.
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    Registered User hindude's Avatar
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    Quote Originally Posted by Donkey View Post
    It is not a boost leak. You do not need the HWG map. It is supposed to taper down like that. You even posted the info from Cobb's map notes in your first post:

    Boost Targets: ~16.5psi peak boost pressure tapering down to ~13.5psi by the 7000 RPM redline, +/- 0.8psi."

    The car will always have more trouble controling boost in 4th and 5th gear since the WGDC is a somewhat global table that does not have per gear compensation.
    I understand that I am still within the guidelines of the notes for the map, but I was under the impression that I would see a curve such as this:



    A big thanks to Rodman who logged and shared this 3rd gear pull in his 2012 WRX using the same OTS map I am using. I know that every OTS map will be slightly different on every car and the ambient conditions from when he logged vs. when I logged will affect this, but I am just posting this because I was expecting to see a curve like this from my log.

    I guess my log is similar to this except for the spike to 16.5 that Rodman saw, but there are too many variables that could affect that. Everyone has convinced me, for the most part, that I don't have a boost leak, but I think I might do some more logs to see if my results vary.

    After more logs how low of an average peak boost would warrant trying out the Higher Wastegate Map? Would I cause any harm by trying it out now and logging with that?

    Thanks again everyone for the help.
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  12. #11
    Master Baiter EJ257's Avatar
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    Quote Originally Posted by hindude
    I understand that I am still within the guidelines of the notes for the map, but I was under the impression that I would see a curve such as this:

    [image removed to conserve space]

    A big thanks to Rodman who logged and shared this 3rd gear pull in his 2012 WRX using the same OTS map I am using. I know that every OTS map will be slightly different on every car and the ambient conditions from when he logged vs. when I logged will affect this, but I am just posting this because I was expecting to see a curve like this from my log.

    I guess my log is similar to this except for the spike to 16.5 that Rodman saw, but there are too many variables that could affect that. Everyone has convinced me, for the most part, that I don't have a boost leak, but I think I might do some more logs to see if my results vary.

    After more logs how low of an average peak boost would warrant trying out the Higher Wastegate Map? Would I cause any harm by trying it out now and logging with that?

    Thanks again everyone for the help.
    You're within the target range of the map, so you don't need to use the HWG map. You're a little below target, but that's fine. Get a log on a flat road and see what that boost plot looks like, if you'd like. Until then, keep the regular map.
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  13. #12
    Hell on Wheels Rodman's Avatar
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    I was logging, A/F Learning, Boost, DAM, Fine Knock, Feed Back Knock and RPM. Anyone know
    if that is to many lines for an accurate log on the AP? Ambient temp was 45 deg. yesterday.
    It was also before dinner so.. less weight. yea, less weight.
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  14. #13
    Master Baiter EJ257's Avatar
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    Quote Originally Posted by Rodman
    I was logging, A/F Learning, Boost, DAM, Fine Knock, Feed Back Knock and RPM. Anyone know
    if that is to many lines for an accurate log on the AP? Ambient temp was 45 deg. yesterday.
    It was also before dinner so.. less weight. yea, less weight.
    I wouldn't bother with AF Learning on a WOT log, as it becomes obsolete...
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