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Thread: safe boost level for 2.5 uncommon block

  1. #1
    Mitsu booster
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    safe boost level for 2.5 uncommon block

    I just bought an 88 csxt with a 2.5 turbo motor out of a caravan. The turbo has been tweeked with a little and the boost is set at about 18lbs of boost. the motor is an uncommon block, and i was wondering what a safe boost level is for the bottom end and the turbo. It is the factory turbo. The motor doesnt have a ping when you step on it.

  2. #2
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: safe boost level for 2.5 uncommon block

    Welcome to the site!

    What map sensor and injectors are in there? 18PSI is more than what a factory cal should allow. There isn't a hard and fast answer to your question, but if you give us some more details we can help you to make a more informed decision.

  3. #3
    Mitsu booster
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    Re: safe boost level for 2.5 uncommon block

    As far as i know the injectors are stock, but it has an adjustable regulator on the fuel rail. And the map is stock.

  4. #4
    Mitsu booster
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    Re: safe boost level for 2.5 uncommon block

    the previous owner installed a manual boost controller

  5. #5
    Mitsu booster
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    Re: safe boost level for 2.5 uncommon block

    sorry i keep forgetting things. It also has an aftermarket blow off valve.

  6. #6
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: safe boost level for 2.5 uncommon block

    Is it intercooled? What computer is in it? Do you know for sure what injectors are in there? I pray you're not running a 2.5 at 18PSI on a 2.2 cal. I'm guessing not because that would probably be a short love affair with speed.

  7. #7
    Mitsu booster
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    Re: safe boost level for 2.5 uncommon block

    It does have an intercooler and i believe it still has the original computer. The way the previous owner has it setup is he has a t in the line leading to the map that vents the air out before reaching the map. The boost is controlled through a grainger valve

    - - - Updated - - -

    So I guess the better question now is what is a safe level to turn it down but still being above the stock level?

  8. #8
    Mitsu booster
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    Re: safe boost level for 2.5 uncommon block

    The injectors are also stock

  9. #9
    Visit www.boostbutton.com... Turbo Mopar Contributor ShelGame's Avatar
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    Re: safe boost level for 2.5 uncommon block

    How do you build a non-common block 2.5? Is it a tall deck block? If it is, those rods are like extended length LW rods. I wouldn't run too much boost on them. Also, they run the 2.2 turbo piston; which has a dish, but it's not enough dish for boost, really. The CR is like 9:1 on those engines.

    On the other hand, there were no 2.5 turbo from the factory that were not common block. So, if it's a factory 2.5 turbo from a minivan, you should be good to go. It will have T2 rods, and decent pistons (if they're original).

    And, finally, especially if it's engine #1 above, running on a 2.2 computer at 18psi - it doesn't have much left in it. It's a ticking bomb.

    EDIT: the easy way to tell a CB from a TD, is the fuel pump block-off. A tall deck or early block will have one (to the left of the oil filter). A CB will not, generally. There are some later CB service blocks with the fuel pump mount.
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  10. #10
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: safe boost level for 2.5 uncommon block

    Assuming that it's a 2.2 computer until it's confirmed that it's a 2.5 computer or custom cal, I would turn it as low as you can go. Running a 2.5 on a 2.2 computer will give too little fuel and too much timing. It's very bad for business.

    - - - Updated - - -

    ETA: Good catch Rob.

  11. #11
    Mitsu booster
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    Re: safe boost level for 2.5 uncommon block

    Ok thank you. Then it must be a common block. Because I know that the motor came out of a turbo caravan but I'm not sure what year caravan it came out of. But if they were all common blocks then great. I appreciate your help on that one

  12. #12
    Mitsu booster
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    Re: safe boost level for 2.5 uncommon block

    I would take your advice now and confirm that it is a cb but the car isnt right in front of me now

  13. #13
    Mitsu booster
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    Re: safe boost level for 2.5 uncommon block

    So if it is a common block, i can run 18lbs? And there is an adjustable regulator on the fuel rail, so the fuel has been tampered with. And the car doesnt run too lean or too rich. The previous owner also installed an air to fuel gauge.

  14. #14
    Visit www.boostbutton.com... Turbo Mopar Contributor ShelGame's Avatar
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    Re: safe boost level for 2.5 uncommon block

    Even if it's a common block, I'd get the right computer for it. If it's running a stock 2.2 computer, it will not have enough fuel, and too much timing, as Cordes said...

    If you get the proper computer, MAP, and injectors, 18psi on a stock 2.5 is not out of the question.
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    Rob Lloyd
    '89 Daytona C/S

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  15. #15
    Mitsu booster
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    Re: safe boost level for 2.5 uncommon block

    Awesome, thanks. Now what about the turbo? Can i run it on 18 lbs?The turbo is still the factory one that came on the 2.5

  16. #16
    Visit www.boostbutton.com... Turbo Mopar Contributor ShelGame's Avatar
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    Re: safe boost level for 2.5 uncommon block

    Quote Originally Posted by 1988CSXT View Post
    Awesome, thanks. Now what about the turbo? Can i run it on 18 lbs?The turbo is still the factory one that came on the 2.5
    Assuming it's in good working order, sure. The little Mitsu won't do much higher than that, though.
    https://db.tt/SV7ONZpQ
    Rob Lloyd
    '89 Daytona C/S

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    13.24 @ 100.5mph
    NHRA #3728 AF/S

    boostbutton.com
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  17. #17
    turbo addict Pat's Avatar
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    Re: safe boost level for 2.5 uncommon block

    What number CSX is it? If it's the one I'm thinking of, then I know a bit about it.

  18. #18
    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: safe boost level for 2.5 uncommon block

    Considering the thing that usually breaks is pistons and not rods, and considering the difference between 2.2 and 2.5 pistons, i'd venture a guess that a non turbo tall block 2.5 is just as good for a mild turbo setup as a common block turbo 2.5 is.

    The bottom end can handle a ton of power, it just can't take carelessness and lack of any attempt at proper tuning. You'll need a wideband, a proper base calibration for your engine combo, and patience!

    Once you have a safe tune in place the mitsu turbo, stock injectors, and stock intercooler all 'max out' just over 200hp, which, believe it or not, is a solid high 13 on slicks in that car.

    Or, maybe 13.3 if you're really damn good. Gasketmaster did it in a 2.5/mitsu/5spd shadow at one point.

    Dont push the red button.You hear me?

  19. #19
    Supporting Member Turbo Mopar Contributor GLHS60's Avatar
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    Re: safe boost level for 2.5 uncommon block

    Has anyone, beside me, ever run a 2.5 T-I engine with a 1988 2.2 T-I SMEC or the other way around??

    I've swapped 1988-1989 T-I SMEC's between 2.2 T-I and 2.5 T-I's several times over the years, just because it's common knowledge that it "wont work," and never had any problems. The fuel part just adds up to me and the spark didn't seem to make any difference although I never ran more than 14 psi . I only know enough about electronics to be dangerous but "I just had to try" !!

    T-II is a different story.

    Thanks
    Randy


    There is no logical reason to call an Engine a motor.

    Randy Hicks
    86 GLHS60
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  20. #20
    Hybrid booster
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    Re: safe boost level for 2.5 uncommon block

    Quote Originally Posted by Pat View Post
    What number CSX is it? If it's the one I'm thinking of, then I know a bit about it.
    I second this inquiry, I may have intimate knowledge to share.

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