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This is a discussion on Questions on stage 2 upgrade (downpipe/ap) within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; thanks for clearing that up zax...

  1. #16
    Registered User Ruh Roh's Avatar
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    thanks for clearing that up zax

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    Registered User 11blackwrx's Avatar
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    I was told this can be tuned for to correct. They advised to get an ebcs and then a retune
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    zax
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    Quote Originally Posted by 11blackwrx View Post
    I was told this can be tuned for to correct. They advised to get an ebcs and then a retune
    That will eliminate boost spiking, a completely different phenomenon but often confused with boost creep.

    Tuning turbo dynamics may help, but it's not a magic solution. If the Wastegate is truly incapable of diverting your exhaust from the turbine, the tune will likely not help. You can also opt to port and polish the wastegate.
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    Quote Originally Posted by zax View Post
    Boost creep [most often] means that the wastegate is not able to open completely or is sized too small for the amount of air the motor is flowing, allowing the boost to continue to build past the target boost. With the WRXs prior to 2009, the Mitsubishi turbos have an adjustment on the wastegate actuator arm. However, VF series turbos do not have this adjustment. There are a few ways around this:
    1.) Replace the IWG with EWG (this requires a tune regardless)
    2.) Replace the IWG spring (there are threads on how to do this with STi turbos, the same concept applies to the VF52)
    3.) The boost control is a PI (proportional, integral) closed-loop control system. There is an equivalent to anti-windup within the Turbo Dynamics tables. Tuning this MIGHT remove the boost creep. However if the boost creep is truly caused by the wastegate not opening completely, there's not much you can do from a tuning perspective.

    Truly, the best solution is to add a little bit of back-pressure (i.e. high-flow cat) to decrease the pressure differential across the turbine. Running a LWG or HWG map is only for target boost, not for boost creep/wastegate creep (which can be easily tuned out with Turbo Dynamics)
    I agree with a lot of this... A few thoughts from my point of view:

    I only agree with point 1.) here in the sense of true boost creep. Points 2 & 3 are suggestions to eliminate other issues which may appear to be boost creep.

    To check for boost creep (and hence isolate tuning issues - THIS IS IMPORTANT) - set all wastegate controls to zero (or just plug the CORRECT boost control tubes mechanically). If you have more boost at throughout any part of the power band than your wastegate spring pressure (normally 7psi for stock IWG), you are boost creepin'. Stop it. It's due to the wastegate being TOO SMALL to properly vent the needed air around teh turbine... forcing more air through the turbine... spinning the compressor faster... and then creating even more boost which can't be vented around the turbine. Feedback system fail.

    To give you an idea, here is a log of my boost pressure on a WOT 3rd gear pull with the waste gate actuator tied direct to the manifold pressure (no boost control other than the wg spring):


    Note how I don't even want to run that much boost at redline or 5k rpm... but have no choice. The system just keeps going further and further out of control without the feedback to bring it back inline.

    Having this issue not only effects WOT stuff at redline. It makes boost control extremely difficult. Anybody that has driven a car with intermittent boost spikes and inconsistent control can show sympathy. Smooth boost control is required for a proper feeling power band.



    For the record, if you are catless in a 3g car, expect to have to work around some issues. Some basic concerns that everybody should look into while considering having a catalyst (or lack thereof) in their exhaust:

    -Do you feel like fighting with emissions? In PA, even in counties without emissions, the presence of a catalyst is confirmed via an "anti-tampering check" that is included with the safety inspection
    -Catalysts are destructible. Keep this in mind. If you are getting frequent tunes or messing with your tune itself, it is possible to destroy your catalyst quickly. Extra fuel in a catalyst does not end well.
    -Catalysts are expensive. This cost may be outweighed quickly, however. An EWG kit is far more expensive than a catalyst. So is failing multiple safety/emisison tests. Dropping a bellmouth down pipe becomes a miserable process when a v-band EWG is right by it.
    -Performance. This is a heated subject. I personally feel that the car should not have a catalyst in its exhaust track. The changes in my boost control tables were quite remarkable once it was out - which could have been due to the larger down pipe anyhow. The tune must be made to cater to this lack of back pressure one way or another. Expect to change your turbo dynamics tables a bit as well as your wgdc tables. From a torque point of view, you'll have to account for this when doing your timing tables or AVCS tables.
    -Smell. Yup. Cars are smelly without catalysts. Your little sister, mother, and/or girlfriend will most likely complain or ask about it. If it's your wife, just get a new wife.
    -Random complications. I have had closed loop fueling disabled in my tune for about a year. The newer cars don't like having that rear o2 sensor messed with. A/F Correction #3 and the closed loop fueling targets get screwy after a while. Mine was idleing around 12afr and NOT happy until I disabled closed loop fueling. Now that the definitions for the tune are out there, the issue has subsided. Just be prepared for it.
    -Modifications down the road. If you plan on adding an EWG... I'd go catless. I don't think you'll be able to fit the dump pipe and hardware in there with a catalyst. It's tight. Also, if you are planning on big power, I'd recommend going catless.
    -Trees. They are worth considering to many.

    Alright. So there are my thoughts on both boost creep/spikes and your decision on going catless or not. =)
    Last edited by Heide264; 11-05-2012 at 10:10 AM.
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  7. #21
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    I knew you'd chime in with some great info Brandon . A few things I'd like to clarify:

    Quote Originally Posted by Heide264 View Post
    Modifications down the road. If you plan on adding an EWG... I'd go catless. I don't think you'll be able to fit the dump pipe and hardware in there with a catalyst. It's tight. Also, if you are planning on big power, I'd recommend going catless.
    There are a number of catted Downpipes such as the Cobb and TurboXS that place the Cat close to the rear of the downpipe (in front of the rear O2 sensor):



    This shouldn't cause fitment issues with EWG uppipes.

    This leads to my second point:

    Quote Originally Posted by Heide264 View Post
    Performance. This is a heated subject. I personally feel that the car should not have a catalyst in its exhaust track. The changes in my boost control tables were quite remarkable once it was out - which could have been due to the larger down pipe anyhow. The tune must be made to cater to this lack of back pressure one way or another. Expect to change your turbo dynamics tables a bit as well as your wgdc tables. From a torque point of view, you'll have to account for this when doing your timing tables or AVCS tables.
    Downpipes that place the catcon in the rear of the pipe will have similar performance to a catless downpipe for the following reasons: the exhaust has cooled in the course of it's 18" travel. Cooler exhaust is denser and has less pressure, and consequently will induce less pressure up-stream. Placing the catcon further upstream helps facilitate the catalytic reaction necessary to remove the excess fuel from the exhaust due to the increased exhaust temp. However, it will slightly reduce the flow of exhaust over placing it downstream. Either one has shown to cause little decrease in power for any application under 350whp. The 2.5" taper in the Cobb downpipe is a much bigger concern.

    Furthermore, the WRX does not apply camshaft phasing on the exhaust lobes. Tuning the AVCS tables on the STi will allow for much more dynamic gains in torque.
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  8. #22
    Registered User Heide264's Avatar
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    Great points zach.

    I never realized they had down pipes like that. Provided you don't have to pass a sniffer test, that would be a great work around from the traditional location. I believe the cat has to be close to the turbo to take the nitrogen compound out of the exhaust.

    Also, on the AVCS approach, I believe just varying the intake valves would give you a lot of the same effect. You can still get more or less valve overlap to deal with the exhaust scavenging, lack thereof scavenging, or exhaust gas recirc. AVCS is a difficult beast to fight with and I'd really only recommend it to a well established tuner.

    Hopefully this clears up some of the confusion though. I feel like there is a pretty healthy amount of information in here.
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    Quote Originally Posted by pauller View Post
    Boost creep! Forgot to mention that. So how big of an issue is it? (Sorry for the bombardment of questions...)
    Boost creep on the 08+ can be very annoying. On the company car we tried getting it tuned out but still ran into issues in the long run. The solution was an external wastegate. This being said its rare that a pro-tune will not eliminate boost creep. If you do end up getting an accessPORT and running into boost creep while stage 2 Cobb does make lower/higher wastegate duty cycle maps to help eliminate boost creep however this may not remedy the issue either.

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    It is difficult to tune for it simply because it is a 100% mechanical issue. Only thing you can do is remove the fuel cut ability the ECU has (tuning), port the IWG, or add an EWG.
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    Well, a month later and I have a Nameless Axleback Muffler Delete, Tomei Catless DP and of course a Cobb AP with a Stage 2 91 tune. I'm with a stock midpipe though and my friend brought up that it kind of defeats the purpose of an extremely high flow DP just for it to go into the stock midpipe and then out a high flow axleback. So would it be smart just to swap for a catback and subsequently have a full turbo back or just keep my current set up with the stock midpipe?
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  12. #26
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    Questions on stage 2 upgrade (downpipe/ap)

    Quote Originally Posted by pauller View Post
    Well, a month later and I have a Nameless Axleback Muffler Delete, Tomei Catless DP and of course a Cobb AP with a Stage 2 91 tune. I'm with a stock midpipe though and my friend brought up that it kind of defeats the purpose of an extremely high flow DP just for it to go into the stock midpipe and then out a high flow axleback. So would it be smart just to swap for a catback and subsequently have a full turbo back or just keep my current set up with the stock midpipe?
    I've got similar parts as you do and I asked my tuner if I should find a mid pipe or go full exhaust... He said if I want to spend the money for a full exhaust then sure but the numbers won't move much and buying a midpipe is not worth it. So save the money other stuff.

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    Nameless Turbo back exhaust

    I'm a new owner of a 2013 WRX Limited Hatch myself. Bought a Cobb AccessPort from a fellow board member here for a good price. Just last week I was able to get the firmware upgrade from my '13 model and installed the Stage 1 93 normal wastegate. I'm very impressed with the performance difference! More fun then my 2007 BMW 335i with Dinan Stage 2 upgrade. Must be the AWD .

    Will be upgrading in a couple months to the Nameless Turboback muffler delete system. Like the look of the Nameless Downpipe with the long wastegate pipe separation. Figure the system will be better tuned if I purchase as a complete set. Don't really plan on anything more after this upgrade for the driveline. Might spend some money on suspension and brake upgrades but the power from a Cobb OTS Stage 2 93 will be plenty for me.

    Never keep a car more than 2-3 years so being able to revert back to stock form is important; better trade in value that way and I usually get 1/2 my upgrades money back too.

    Oh, my WRX is the 29th new car I have purchased. Really want number 30 to be special, time will tell.

  14. #28
    Registered User yeaitsgotaturbo's Avatar
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    Watch this video. Nameless catback. Cnt catted downpipe.Cobb intake. PW Tmic Cobb ap stage 2 91oct. Car is much faster than stock. My guess would be 320/360

    2011 wrx 1st gear stage 2 - YouTube

  15. #29
    Registered User matsayz's Avatar
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    Quote Originally Posted by yeaitsgotaturbo View Post
    Watch this video. Nameless catback. Cnt catted downpipe.Cobb intake. PW Tmic Cobb ap stage 2 91oct. Car is much faster than stock. My guess would be 320/360

    2011 wrx 1st gear stage 2 - YouTube
    which nameless exhaust is that?

  16. #30
    Registered User yeaitsgotaturbo's Avatar
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    Nameless sedan cat back is all i know. no mufflers no resonsator

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