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Thread: Big Exhaust = BIG Boost Creep?

  1. #1
    Garrett booster
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    Big Exhaust = BIG Boost Creep?

    Howdy y’all. I can’t figure out if I have a huge problem or no problem at all. I’ve been running a modified stock cal (3 bar) on a 2.5l with a TII Garrett and auto trans. 2 1/2 inch exhaust with little to no restrictions.

    Until I get my bigger injectors back from Cindy, I’m keeping my boost around 10psi. But when I go past 4000rpm, boost gets a little out of control until it hits my 15psi cut off set in the cal.

    I seem to remember somewhere on Donovan’s site explaining that a big exhaust leads to boost creep and that the easiest thing would be to add more fuel to take advantage of it.

    I guess my question is this: if I turn up the boost (with more fuel obviously), will that eliminate the boost creep? Should I consider introducing a restriction in the exhaust for better boost control???

  2. #2
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Big Exhaust = BIG Boost Creep?

    It may or may not help to up the boost. Your best bet is to port the WG hole in my opinion.

  3. #3
    Hybrid booster
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    Re: Big Exhaust = BIG Boost Creep?

    Larger exhaust is likely not the issue. I've run 2.5" and even 3" with no cat or muffler and didn't have an issue. Only time I've had boost creep issues have been leaking wastegate cans. In my opinion, the only time changing exhaust backpressure creates issues with boost control is with the VNT turbo systems.

  4. #4
    Garrett booster
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    Re: Big Exhaust = BIG Boost Creep?

    Thanks gents. I’ll look into porting!

  5. #5

    Re: Big Exhaust = BIG Boost Creep?

    You could try and add some restriction into the exhaust to see if that helps...

  6. #6
    Slugmobile & MeanMini Caretaker Turbo Mopar Contributor wheming's Avatar
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    Re: Big Exhaust = BIG Boost Creep?

    Agree with others here. Carefully check and test wastegate circuit first. Check lines, fittings, and wastegate can and arm for proper operation.
    I use a MityVac set on pressure to pump up lines and check wastegate can. It should hold pressure.
    Any leaks is like introducing a bleed, raising boost setting. Sometimes cracked tubing only releases pressure when the pressure is higher.

    Sent from my ONEPLUS A6000 using Tapatalk
    Wayne H.

    '91 Dodge Spirit ES 2.5L turbo 5spd
    '05 PT GT 2.4T HO autostick (RIP)
    '89 Plymouth Acclaim 2.5L turbo auto, "Slugmobile" yes, THE Slugmobile!
    '89 Dodge Caravan SE 2.5L turbo auto, "Mean Mini" yes, Gus' Mean Mini! (Current best 11.699 @ 114.43 mph! - Oct 15th, 2022 Cecil County Dragway, MD)
    MeanMini dragracing videos: https://www.youtube.com/playlist?lis...URZLB1RxGYF6vw
    and other cars, trucks and motorcycles
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  7. #7
    Garrett booster
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    Re: Big Exhaust = BIG Boost Creep?

    Funny you say that. I just got a new mityvac kit (replacing my cheaper plastic one). I’ll give that a shot!

    what pressure am I looking for with a stock 89 T2 can?

  8. #8
    Slugmobile & MeanMini Caretaker Turbo Mopar Contributor wheming's Avatar
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    Re: Big Exhaust = BIG Boost Creep?

    I had to get a new one a few years ago, so went with the nice metal one now.

    I would think that wastegate is probably a 7psi one. But not sure. Has to be able to open to make your minimum boost.
    It will take more psi to push it full open.

    Mainly check that it opens normally looking, and can hold pressure. Pump it up from a part of the tubing by the wastegate solenoid. This way you pressurize the entire line and look for leaks. You can use soapy water if you keep it under pressure. Replace any line cracked and making bubbles.

    Sent from my ONEPLUS A6000 using Tapatalk
    Wayne H.

    '91 Dodge Spirit ES 2.5L turbo 5spd
    '05 PT GT 2.4T HO autostick (RIP)
    '89 Plymouth Acclaim 2.5L turbo auto, "Slugmobile" yes, THE Slugmobile!
    '89 Dodge Caravan SE 2.5L turbo auto, "Mean Mini" yes, Gus' Mean Mini! (Current best 11.699 @ 114.43 mph! - Oct 15th, 2022 Cecil County Dragway, MD)
    MeanMini dragracing videos: https://www.youtube.com/playlist?lis...URZLB1RxGYF6vw
    and other cars, trucks and motorcycles
    https://www.youtube.com/user/SlugmobileMeanMini

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