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This is a discussion on Boost creep / fuel cut within the STi Technical Forum forums, part of the Tech & Modifying & General Repairs category; I just spoke with a sales rep from Cobb. He said that a flat plate design will not work well ...

  1. #16
    Registered User WRX88's Avatar
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    I just spoke with a sales rep from Cobb. He said that a flat plate design will not work well with stage 2. He also said that boost creep should not be experienced on the 06 when running catless. He said that should boost creep occur (he said this usually only occurs durring sever cold weather), it can be resolved by simply adjusting the wastegate actuator arm. Sounds like a good argument to go catless. Any feedback?

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  3. #17
    Registered User 409industries's Avatar
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    No EMS can take care of boost creep. It is a physical restriction of the wastegate size.
    Thats interesting because i had creep with my setup (04 STi Catless 3" vishnu TBE) and when i got my Cobb stage 2 AP, my creep went away. I'm not sure why this is either, because i am still seeing the same, if not increased boost levels. Either way, im happy that i am running smoothly again WOT in 5th and 6th gears.

  4. #18
    Moderator YBNormal07's Avatar
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    Quote Originally Posted by WRX88
    I just spoke with a sales rep from Cobb. He said that a flat plate design will not work well with stage 2. He also said that boost creep should not be experienced on the 06 when running catless. He said that should boost creep occur (he said this usually only occurs durring sever cold weather), it can be resolved by simply adjusting the wastegate actuator arm. Sounds like a good argument to go catless. Any feedback?
    I would not recommend adjusting the WG arm. Thats just me. They are a bit more delicate than they appear, and getting it back to stock adjustment can be a pain.

    I'm not knocking Cobb, but the key word here is "should". Regardless of any programming fixes, it is the physics involved that can't be overlooked. I think that with the smaller turbo on the 06 WRX when compared to the VF39 on the STi, the chances are definitely less likely. However, there have been some reports of folks experiencing creep/fuel cut with the Cobb AP. I know for a fact my 04 STi did it.

    If Cobb is saying that the WG adjustment (either the arm or the duty cycle) can resolve boost creep, I say it is actually merely limiting it, and in doing so reducing the performance potential. Not a big deal to be honest as technically, the fix I use (HF cat) is doing the same thing.

    But think about it. If the WG size is such that even wide open it does not provide enough flow, how can adjusting duty cycle or arm travel fix it? It can't "open it more"...'cause it's already wide open. I'll be happy to debate that with anyone. The only real answer is an external WG.
    My advice is to go ahead and install what you want to install, and if you do experience creep or fuel cut, deal with it then. If you are buying quality parts, you'll get your money back if you need to swap with something else. That is ultimately the route I took myself.
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  5. #19
    Moderator YBNormal07's Avatar
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    Quote Originally Posted by 409industries
    Thats interesting because i had creep with my setup (04 STi Catless 3" vishnu TBE) and when i got my Cobb stage 2 AP, my creep went away. I'm not sure why this is either, because i am still seeing the same, if not increased boost levels. Either way, im happy that i am running smoothly again WOT in 5th and 6th gears.
    Good semantical point. I guess I should have said "No EMS can take care of the size restriction of the wastegate which is the main culprit for boost cree".

    Glad to see your AP took care of it though. Like I've said. Sometimes you get it, sometimes you don't. I never got creep until I took it to the track (2.9 mile Summit Raceway) and then *wham*, I thought I blew the engine on the main straight at 138 mph. I NEVER wanted to feel that again so took steps to address it. It worked for me. I still think that under the right conditions, no amount of tuning can prevent boost creep without affecting performance.
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  6. #20
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    hi

    i got 2,0L STi 265 hp europe version

    i have 3" invidia downpipe and 3" blitz exhaust

    the boost pressure is now peaks max 1,6 bar and it holds 1,2-1,3 bar and this is in ALL gears

    is it safe ???

    with stock downpipe it is around 0,9-1,0 bar and peaks too 1,5 bar

    can you help me ? :S
    Subaru Impreza STi03 - 12,382 @ 106,38 miles

  7. #21
    Registered User StupidMan's Avatar
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    YB, I think Ive been experiencing a similar issue with my 06 vf39 wrx. I have slightly enlarged the restrictor pill over what cobb said, and still have the issue. According to the AP, I am hitting 18-18.3 in 2nd-5th while target boost is 16.5 +/- .7 (psi)

    Do you remember what trouble code was thrown when you hit fuel or boost cut? Mine was p0244 or wastegate solenoid duty: range. This makes me believe it is boost creep or hunting and not spike.

    I was thinking about putting a 50MM HKS WG leftover from my rx on the up pipe and plumbing it into the DP. It would still work for any bolt on turbo upgrade. And it looks so friggin easy to do compared to what Im used to. Plus I miss that big wastegate sound
    stupidman has spoken

  8. #22
    Moderator YBNormal07's Avatar
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    I can't recall exactly what the code was, but I believe that was it (an EVO owner had a code reader at the track thank god!).

    If you are going to an alternative wg, and will be plumbing it back, 50 MM is definetly large enough (I think the tien WG that most folks use is like 41-42MM). Of course, you can also plumb it to atmosphere if you don't mind the noise!

    Obviously you'll need to adjust/tune for it, as it is the physical regulator of your boost.
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  9. #23
    Registered User StupidMan's Avatar
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    Thanks,

    Yeah I doubt I would plumb it into the atmosphere. I had it like that on my rx7 and I swear it almost made people wreck when It was fully opened and I buzzed by. Plus it is stinky.
    stupidman has spoken

  10. #24
    Registered User orvtech's Avatar
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    Quote Originally Posted by YBNormal07
    OK,
    I've been answering a lot of question lately about DPs without cats, fuel cut, boost creep, etc. so I thought I'd put a stickey in place. The following is a simplistic explanation. Feel free to respond and correct any errors I've introduced, or provide further clarification. This is to be an instructional stickey, so more information is always better.

    No EMS can take care of boost creep. It is a physical restriction of the wastegate size.

    Exhaust flow powers the turbine side of the turbo, spooling up the impeller and compressing your intake air to your manifold.

    To control boost, you regulate the flow of this exhaust by bypassing exhaust around the turbo once it achieves set pressure. The wastegate is the exhaust bypass around the turbo. As you close the wastegate, this directs more flow through the turbo, increasing boost. As boost rises to set pressure, the wastegate opens to allow exhaust to bypass around the turbo, slowing the turbo down and lowering/maintaining peak boost pressure. In reality, the wastegate is merely a bypass valve though, not a true pressure contol system.

    On the stock system, you have backpressure in your exhaust line from the cat, resonator, muffler, and piping sizes. This works to keep the exhaust flow through the turbo to a rate that can be managed in conjunction with the wastegate.

    Once you remove these items and free up exhaust flow (reduce backpressure), your turbo now has more exhaust flowing through it at peak throttle than it did before. The wastegate is sized with the stock backpressure in mind. It now can't flow enough exhaust at peak pressure to slow the turbo down, leading to a slow buildup in peak boost pressure, otherwise known as boost creep. This ultimately leads to an overboost condition, usually exhibited by a CEL and fuel cut (your car suddenly lurches and dies or cuts out and back in at full throttle.....a horrible experience believe me!!!!)

    The only way around this is to
    1. enlarge the wastegate hole (porting the wastegate)
    2. increase the exhaust backpressure (high flow cat or keep the stock catback with a catless DP)
    3 or use an external wastegate.

    Of the 3, the external WG is probably the best as you can buy one that controls boost in both directions, unlike the internal wastegate the stock turbos come with. Plus the sound it makes is awesome!

    Personally, I've always erred on the side of caution and used a DP with a HF cat. No boost creep to date with this setup (on my STi and Legacy). Prior to the HF cat though, I did experience boost creep at a track day once. It is not something I enjoyed as I thought my STi had blown it's engine. Luckily for me, it was just overboost.

    I have not personally verified using a catless DP with the stock catback exhaust to ensure creep does not occur, but it makes sense so I suspect it will work the same as a catless DP. I prefer the HF cat route though, as it is still emissions friendly and precludes having to swap the stock DP back in to pass emissions. The HP loss is negligable so I consider it the best of both worlds.

    Comments welcome!
    how about DP that separate wastegate output from turbo output like maddad DP, it by pass the sensor.

  11. #25
    Registered User WRX88's Avatar
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    Is boost creep a problem even if it doesn't cause fuel cut? Need to know because I'm going stage 2 on my 06, fully catless and i don't have a boost guage. Fuel cut is the only way i will know(but hopefully i won't) if i am experiencing boost creep.

  12. #26
    Moderator YBNormal07's Avatar
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    Quote Originally Posted by orvtech
    how about DP that separate wastegate output from turbo output like maddad DP, it by pass the sensor.
    Not sure what you are asking here? What sensor does it bypass? Boost is measured at the intake manifold...not the exhaust.
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  13. #27
    Moderator YBNormal07's Avatar
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    Quote Originally Posted by WRX88
    Is boost creep a problem even if it doesn't cause fuel cut? Need to know because I'm going stage 2 on my 06, fully catless and i don't have a boost guage. Fuel cut is the only way i will know(but hopefully i won't) if i am experiencing boost creep.
    Boost creep by itself isn't an issue...it's the results that suck. Fuel cut will likely occur with creep. I really don't get why you don't have a goost gauge though. You have a turbo motor...you need to know what it is doing otherwise it's kind of asking for trouble.
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  14. #28
    Registered User WRX88's Avatar
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    I am not at stage 2 yet. I will be on friday. I don't plan on driving hard until i get at least a boost guage. But you answered my question perfectly.

  15. #29
    Registered User TheReaper's Avatar
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    My friend has an 05 STi with a catless turbo back and at first he did have boost creep whenever he would get around 100mph under full throttle and he said he it went away one day with out him even noticing that it went away (he wasn't thinking about the boost creep not happening anymore) and ever since it went away he hasn't had 1 single issue with boost and he still has the same catless tbe and no other additional mods.
    You might be a king or a little street sweeper but sooner or later you'll dance with the reaper.

  16. #30
    Registered User abtgolf's Avatar
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    Quote Originally Posted by TheReaper
    My friend has an 05 STi with a catless turbo back and at first he did have boost creep whenever he would get around 100mph under full throttle and he said he it went away one day with out him even noticing that it went away (he wasn't thinking about the boost creep not happening anymore) and ever since it went away he hasn't had 1 single issue with boost and he still has the same catless tbe and no other additional mods.
    All these boost creep topics are sooooo confusing. i read a lot about it, seems like external wg or porting wg is the best ways to go if you choose to do Catless TBE.

    but what confused me is, some ppl say it won't happen, some ppl say boost creep happened, but went away.

    I am very worry now becuase I bought a RS*R catless dp, with RS*R Exmag exhaust, made appointment to install this Thursday.
    what should I do now? i really don't know....
    should I:

    1. port the WG on the day that I am going to install the exhaust and dp?
    2. order an external wg, wait for it before i install dp or exhaust.
    3. or should i install it, drive easy on my car, gradually push a bit more on gas, see if boost creep will occur, if it does, then order the external wg, or do EM?

    what do you guys think? by the way, I have a 06' STi if this helps answer my questions.

    please help... THANK YOU!!! Thank you.. thank you.
    06' Aspen White STi

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