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Thread: 2.8 Duramax 6L50 to 8L90E swap?

  1. #1

    2.8 Duramax 6L50 to 8L90E swap?

    I am very new to tuning, and I'm wanting to see if this would be something possible to accomplish through HPT? I have a 2017 Colorado 2WD and am wanting to swap the trans to a 4WD 8L90e. The big reason for the swap is I plan on running a compound turbo setup, and the price of an 8L90 vs building a 6L50 to attempt to handle the power is astronomical. Plus if I can gain a few extra gears, why wouldn't I. I know that the V6 runs the 8L45 so the platform has an 8 speed, but I would really like to attempt to run the 8L90E.

    Thank you in advance for the newb questions!

    Kevin

  2. #2
    Advanced Tuner
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    Aug 2016
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    Short answer: Forget it, it's essentially impossible.

    Long answer: Even if any version of the 8sp transmission bolt pattern matches the 2.8 Duramax, which I doubt does, you'd have to find a way to make the Duramax engine control software communicate properly with the 8sp TCM (T87). It's unlikely anybody outside GM could pull that off.

    On top of that, there's no 8L90 OE application in this truck. It's unlikely the Colorado transfer case would mate with an 8L90 transmission.

  3. #3
    I did find that they ran the 2.8/8L90 in the 2017 2500 Express vans, so the trans is out there. They run the same E98PCM/T87(I'm guessing A) TCM. My hope was with the same platform this would be possible, but I'm not finding a lot of hope.

  4. #4
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    Oh! Well, that's somewhat encouraging, then. Thanks for sharing that tidbit. You still have the transfer case challenge. And, you'd have to run the Express van engine calibration to have any hope of it communicating with the TCM. Who knows if that engine calibration can play nice with the rest of the vehicle.

  5. #5
    Quote Originally Posted by tunerpro View Post
    Oh! Well, that's somewhat encouraging, then. Thanks for sharing that tidbit. You still have the transfer case challenge. And, you'd have to run the Express van engine calibration to have any hope of it communicating with the TCM. Who knows if that engine calibration can play nice with the rest of the vehicle.
    The transfer case doesn't bother me as they have converted these to 4x4 already. I really don't want to run the van calibration on the engine as for some reason it's not supported for tuning and that would definitely take away the main reason I'm wanting to swap to this transmission.

    I have a friend who works at a transmission shop. I'm almost thinking grabbing a T87A, getting it unlocked and see what they do when they get plugged in. See if I can somehow get them to talk together. If not I'm out a few hundred dollars and the 6L50 will likely eat those like candy.

    I really wish that I could talk to an 8L90 guru and pick his brain. I realize that this would be a pricy tune, but compared to what it costs to "build" a 6L50, I would be willing to shell out the money! Even if they just give me advice on how I could tune it myself.

  6. #6
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    You don't need an 8L90 guru. Your challenge has nothing to do with transmission calibration. The challenge here is getting the ECM's operating system, which is set up to talk to a 6L50 (T43), to talk to a T87(A), and the issue with that is they speak different languages. So, you're talking about overhauling all of the comms tables, and possibly operating system code.

    As a frame of reference, on the 2015 - 2018 full size trucks and SUVs, in most cases the trucks with the 6L80 vs the ones with the 8L90 came with different operating system software, so that suggests that even the GM software guys couldn't figure out how to make one OS drive both transmission types.

    Beyond the comms issues, there are hundreds of tables and constants, if not thousands in the ECM, not all of which are available in hpt that would need to be updated for the assumption the transmission behind the engine has 8 gears, not 6.

    Honestly, your best bet for success here would be to run the van engine and transmission calibration, and hope it works, but if it's not supported, that's a dead end.

    Alternatively you would need a GM engineer to pull this off.