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Thread: Correct way to upgrade from COS 3 to COS 5?

  1. #1
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    Default Correct way to upgrade from COS 3 to COS 5?

    Im running COS 3 (03190003) on my 2003 Tahoe and would like to go to COS 5 soon. Planning on using the nitrous options to pull timing for towing with the Turbo. That way i can dial in my timing for playing/racing and when i want to hook up the trailer i can flip a switch and not have such an aggressive tune. Engine has had a turbo (Usually 6-15psi, accidently hit 30psi 3 times) on it for the past 225k miles in my silverado and now 35k miles NA in my tahoe so i want it to last a little longer.

    I still have to do the 4L80E swap so im not in a hurry for the COS 5 upgrade. Would like to know the proper way to do the upgrade.

    Thanks,
    Jonathan

  2. #2
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    You cant, COS5 doesnt exist for any 03 OS. You'd have to go to DBC, 02 PCM, and do that to get COS5. You have the best COS option for your 03.
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, starting the mods
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

  3. #3
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    Dang... oh well good try i guess.

  4. #4
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    Wow you have had a turbo for 225k miles that's impressive.

    Wont pulling timing just cause it to boost more? How are you controlling boost why is it hitting 30lbs?

  5. #5
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    Sorry this is a very late reply. I didnt get a email with a new post in the thread..

    But yea its been a great engine. Towed alot with it too.
    Stock lifter took out the cam so i pulled it out and freshened up the top end.

    I had the wastegate in the wrong position which wasnt a issue with the stock exhaust since backpressure was high enough to open it. When i put a muffler on the stock catback it opened up the flow enough to drop the backpressure and had overboost issues.

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