Subaru Subaru Twin Turbos...How To Increase Primary Boost

Discussion in 'Japanese Cars' started by Bushman, Feb 5, 2015.

  1. Bushman

    Bushman New Member

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    After installing boost gauge for mostly diagnostics at this point i noticed primary runs much lower boost than when secondary comes online. A little research on the topic led me to this golden bit of info on how to allow main turbo to run at the ecu limited boost and not lower...its a very simple mod!
    Twin turbo's run a lower boost on the primary turbo (~7psi - ~11psi) and a higher boost when running on both turbo's (~13psi - ~16psi). The primary boost is actually physically limited by way of vacuum line routing limited to a lower boost than the ecu permits. With this simple rerouting mod full boost can be achieved as set by ECU.

    From the developer of this discovery..."The car has been transformed in terms of primary turbo performance and goes like a rocket up to 4000 rpm as well as going like a rocket above 4500rpm (after you get over the VOD!)."
    So people who cant figure out why thier boost controller has no effect on primary i believe this is the answer.
    Once my Stage 0 tune is done and all bugs sorted i am going to try this...in the near future.

    read all about it here
    i read all 10 pages and no one has gone boom

    A similar mod here sold as a "secret" kit here by Nutty, he refurbishes solenoid boxes on exchange(which one can do himself)

    Check Here for another important and easy Subaru Legacy GTB twin turbo vac line mod.

    Warning proceed at your own risk :p
     
    Last edited: Aug 17, 2015
  2. kingsoup

    kingsoup New Member

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    Very interesting! I haven't read it yet, but I'm always on the thought of getting another 99+ car to replace the one I only owned briefly.
     
  3. Bushman

    Bushman New Member

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    Car just came back from shop on the weekend...computer seems to be still learning after reset. When back in bizz im going for this mod!
     
  4. Bushman

    Bushman New Member

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    :D
    [​IMG]
    I am a little concerned with my 2 minute mod 8|
    But the right foot is loving it!
     
  5. jsdub1

    jsdub1 Mister

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    Bushman, I just did this mod myself, WOW what a difference. Have you had any negative effects?

    I wouldn't think there are since line 10 is still connected and ECU has boost control, but looking to see if you've had any negative experience.

    I am just waiting on my restrictor pill to arrive, should be today or tomorrow, and I am going to do the "Line 1" mod. Seems to delay the opening of the Intake Air control valve, so the VOD is greatly reduced! I'll have an extra pill (had to order like 5 to get the minimum order) if you want one!
     
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  6. IMPUL

    IMPUL Collector of fine japanese lawn ornaments

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    I cant see the diagrams. But im guessing your just runing the primary to its own wastegate? Can you load the pics here?
     
  7. jsdub1

    jsdub1 Mister

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    Last edited: Jul 30, 2015
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  8. jsdub1

    jsdub1 Mister

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    http://imgur.com/NwxfDIz,4VqFDGC,OC9AbgE,QxfRhxI

    Pics got reversed agh

    Pic 4 - line straight from manifold to BOV. "T" in line removed
    Pic 3 - metal line ten from solenoid box connecting with line 10 from the passenger side guard and down to the inlet
    Pic 2 - close up
    Pic 1- duplicate of 3?
     
    Last edited: Jul 30, 2015
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  9. IMPUL

    IMPUL Collector of fine japanese lawn ornaments

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    So ya. Primary is controlling itself. And the secondary is ecu controlled.
    Whatever the wastegate can hold it will hold. Probably never cause anyproblems. Thats a pretty sweet free hp mod!
     
  10. jsdub1

    jsdub1 Mister

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    Sure man hahah lots of this turbo system stuff still goes over my head, still so new at this. Learning a lot though.

    The results are great though. Nobody on club sub reported any problems so I'm hopeful.
     
  11. Bushman

    Bushman New Member

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    No problems, I was seeing 15bs boost from primary on up....but now only 10 due to a O2 and mass airflow code to be replaced shortly.
    Line 1 mod? Sign me up!!!
     
  12. jsdub1

    jsdub1 Mister

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    PM me your address, I'll send you one of my spare pills.
     
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  13. Bushman

    Bushman New Member

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    Awsome man thanks! So I got my O2 and MAF sensor (part numbers in GTB thread) and still only 10 lbs boost. Eric my mechanic says check your vac line mod.....shure enough the cap was missing off the tee LOL.
    So back to 15 lbs of boost goodness all over the Rev range. Looking forward to reducing vod.
    You asked me if there where any drawbacks? Hard to economise since it boosts so quickly and easily.