1999 chevy suburban 5.7 vortec to7.4

Discussion in 'GM Powertrain' started by yutyut99, Jun 8, 2010.

  1. yutyut99

    yutyut99 New Member

    this has probably been covered but could not find what iwas looking for.i have a 1999 chevy suburban 4x4 with a 5.7 vortec and want to swap to a 7.4. what year engines should i be looking for and what to look forward to. plan on doing the work myself. have access to lifts stands and tools at work.
  2. Silverado Junkie

    Silverado Junkie Rockstar 4 Years 500 Posts

    Try to get a 7.4l thats a '96 or newer so it will be a vortec like your 5.7l is. They are both four bolt mains that will bolt right up to your tranny and frame as far as I know. Just buy the motor and all its accessories and everyhting that you'll need for it(fluids, sparkplugs, odds and ends,etc.) Then you will have to buy a new computer because the computer for the 5.7l wont run the 7.4l. Good Luck.
  3. silveradotrailblazer

    silveradotrailblazer Epic Member 5+ Years ROTM Winner 5000 Posts

    1999 chevy suburban 5.7 vortec to 7.4

    Your truck has a 4l60e and the big block Suburbans came with 4l80e . I dont think the big will bolt to the 4l60e. Also you will have to change the wiring harness along with the computer.
  4. yutyut99

    yutyut99 New Member

    well i am looking for a truck that ican just get every thing off of at once. that way i can get every thing i will need. but with the 96 and up is it a good fit with the new tranny as far as the transfur case and drive shafts or will ineed new ones.
  5. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    The wiring harness is actually the same accross all models as long as they are equipped the same. and yes from 1996 you can run a 7.4L, and you will need a 4L80E... Everything is a direct bolt in affair and will be basically like changing your 5.7L just with a bit bigger motor and the trany the same.. I would change over the driveshafts since i believe they are a bit heavier duty..
  6. yutyut99

    yutyut99 New Member

    so i wouldn't have to change the harness the ecu will just snap in? also what about the transfer case?
  7. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    I would reccommend the transfercase as well. and yes the ECU plugs in..
  8. 2COR517

    2COR517 Epic Member 5+ Years 1000 Posts

    If you have a 3/4 ton K2500 Sub now, you will already have a 4L80. The NP241/243 is used in all the Subs, so no need to change. Unless you DO have a 4L60 now and swap to a 4L80. Then you will need to at least swap input gears on the T-case. The 4L60 has a 27 spline output shaft, 4L80 has 32 splines. So the input gear of the T-Case needs to match.
    Last edited: Jun 10, 2010
  9. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    X2 i completely forgot to even ask if it was a 3/4ton or a 1/2 ton... and i was reccomending the Tcase swap either way so there are less things to split etc...
  10. yutyut99

    yutyut99 New Member

    it is a 1/2 ton any idea on any thing else that would need to be swaped i have allready gone through the front and rear diff and installed new 4.11 gears. also when looking at used engines what should i be looking for to try to find ane that has not been abused

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