Improve factory boost solenoid for $2.88
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This is a discussion on Improve factory boost solenoid for

.88 within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; Stealing this thread from NASIOC. Some guy here local is raving about this mod, anyone care to shed some light ...

  1. #1
    Registered User wreckingball man's Avatar
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    Improve factory boost solenoid for $2.88

    Stealing this thread from NASIOC. Some guy here local is raving about this mod, anyone care to shed some light on it or point me to a thorough explanation with real data somewhere? It seems sketchy to say the least.

    Improve factory boost solenoid for $2.88 - NASIOC

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    Registered User pete25r's Avatar
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    I don't have any personal experience but in the thread there a few that say it sucked for them. Like boost got better then the car "re-learned" and went back to the way it was.
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    Registered User wreckingball man's Avatar
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    I'm not sure what to make of it. Can someone provide a very detailed description of the process going on here? Just looking for more than, "my butt dyno felt it..." and "it increases the airflow."

    I'm reading these articles right now, so I am getting informed. And feel free to use any precise technical terms you need to explain it properly.
    http://blog.perrinperformance.com/bo...lained-part-2/
    http://www.cobbtuning.com/Technical-...es-s/70674.htm
    Last edited by wreckingball man; 04-09-2014 at 06:33 PM.

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    Registered User pete25r's Avatar
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    You want to improve factory boost?
    EBCS, or hybrid (EBCS and manual). Matty recommends the hybrid I believe.
    I've got a GM EBCS on my 02. It goes for like 30 bucks and builds/holds boost real well. Had to do some soldering and shrink wrapping but I enjoy that kinda nerdy stuff.
    Oh and had to tweak my WGDC table on my map. Lowered it down a good bit the pulled it up a little hear and there.
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    Registered User wreckingball man's Avatar
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    I don't want to improve anything right now, my car runs and holds boost exactly the way it was designed to; that's enough for me lol.

    This was brought up in our local club and I had never heard of this before. The guy is claiming "such an improvement."

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    Quote Originally Posted by wreckingball man View Post
    I don't want to improve anything right now, my car runs and holds boost exactly the way it was designed to; that's enough for me lol.

    This was brought up in our local club and I had never heard of this before. The guy is claiming "such an improvement."
    You clearly don't understand the benefits of improved spool and response.
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    meh. I wouldn't do it.
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    Registered User wreckingball man's Avatar
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    Quote Originally Posted by zax View Post
    You clearly don't understand the benefits of improved spool and response.
    Thank you. I guess that's why I posted this thread.

    So now can you explain the theory as to why this mod works, or doesn't work...or whatever. You're one of the people I was hoping to hear from.

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    Moderator Donkey's Avatar
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    The problem is this mod works for slightly better spool up but will cause overboosting and boost oscillations at WOT. The wastegate duty cycle for the solenoid is tuned to the components of the boost control system. Changing anything (vacuum hose size,restrictor pill size,wastegate "T" ID) throws off that tuning. This mod was created before alot of the tuning solutions came about for the USDM WRX's and is nothing like using a 3 port BCS or even better a hybrid boost control with a good tune. The factory 2 port "bleed" system is the suck.
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    Registered User wreckingball man's Avatar
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    Quote Originally Posted by Donkey View Post
    The problem is this mod works for slightly better spool up but will cause overboosting and boost oscillations at WOT. The wastegate duty cycle for the solenoid is tuned to the components of the boost control system. Changing anything (vacuum hose size,restrictor pill size,wastegate "T" ID) throws off that tuning.
    Awesome!

    I understand in generalities. But can you go into a little more detail as to what actually is happening at the solenoid, at the restriction that's now removed, in the computer, at the wastegate....basically why these things happen? I'm not sure how to frame my question, I guess it would be, can you expand on that answer?

  12. #11
    Moderator Donkey's Avatar
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    Quote Originally Posted by wreckingball man View Post
    Awesome!

    I understand in generalities. But can you go into a little more detail as to what actually is happening at the solenoid, at the restriction that's now removed, in the computer, at the wastegate....basically why these things happen? I'm not sure how to frame my question, I guess it would be, can you expand on that answer?
    I will try to use an analogy. It's like the MAF issue. If you change the ID of the MAF housing the calibration is thrown off right? Becuase the factory sensor was calibrated to a specific ID. To fix the calibration you either rescale the MAF sensor or re install the original MAF housing. Same thing here. You have change the air flow characteristics in the boost control system.The bcs works on a duty cycle. It's not just opened or closed. So once you change the airflow charateristics of the system you have to "recalibrate" the duty cycle of the solenoid. The ECU does not have infinite control. It has defined max parameters along with compensation tables that ALL now need to be recalibrated.

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    Registered User wreckingball man's Avatar
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    Thank you Donkey for following up. I'm not sure I understand what is going on physically though.

    In the instance you apply the throttle, more air is diverted to the EBCS and away from the WG actuator because you have removed the restriction in the line running to the EBCS. And in that moment, you aren't "losing" boost because the WG isn't opening and it builds towards target boost quicker. ...which is perceived by the user as faster spool? Basically, one of the faults of 2 ports is that it's always putting some pressure on the WG actuator. This increased flow to the EBCS reduces the flow to the WG actuator and applies less or no pressure to it, which leads to faster build towards target boost?

    However, through the duration of the pull, this bigger diameter hose is flowing more air than should be allowed, causing it to exceed target boost. The ECU then pulls WG duty cycle back down and more pressure is then diverted back to the wastegate and in turn lowering boost. But this is an overcorrection due to the improper diameter hoses. The ECU sees that it is not hitting target boost for the given rpm and throttle position, and then raises duty cycle. But then again because of the larger diameter hose, it's bleeding more air than it should. And then this happens over and over again in a cycle...which is boost oscillation? And the ECU can't equilibrate because it is assuming the wrong diameter hose. Or is it more complicated lol?

    TL-DR:
    -Can you explain why this mod leads to faster spool up?
    -Can you explain how and why boost oscillation occurs in this case?
    -How does the ECU know what the actual boost pressure is inside the manifold?
    -Are throttle position and rpm the only inputs that the ECU uses when referencing the tables? Would it not also have to determine either an absolute pressure or atm. pressure as well as air temps or am I being dumb?

    ...maybe I'll just take myself over to the FAQ's section on romraider forums

  14. #13
    Moderator Donkey's Avatar
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    It builds boost faster because the bcs cannot bleed the air off quick enough due to the change in airflow. It is basically closed at idle "0" duty cycle. The wastegate arm is always seeing pressure. Hence "bleed" type system. Duty cycle is increased to "bleed" the air off away from the wastegate actuator. The ECU knows what the pressure is in the manifold because every USDM Subaru has a MAP sensor specifically for that. Look the the picture I posted. Especially the names of the tables. ATM = atmospheric IAT = intake air temp.
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