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BBC w/TBI to replace a SBC w/TBI???

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by DUKSRULE, Apr 14, 2003.

  1. DUKSRULE

    DUKSRULE 1/2 ton status

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    OK here is what I was thinking. I have a 91 Sub 2500 with the 4l80 tranny and a 350 TBI. I would like to swap the small block for a big block. Can I use the same wiring harness? I know I will need a bigger throttle body and accessories. The question is will a bigger 454 throttle body plug into the 350 wiring harness? I also assume I would need a 454 PROM for the computer. The distributor should swap over to the big block right? Anyone done this? I want to keep the fuel injection but would like to get the power of a big block.
     
  2. DukeBoy88

    DukeBoy88 1/2 ton status

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    The harness should be the same. you'll need a custom 350 prom though I believe, I recomend Ed Wright's programing. The 454 TB should plug in. Not sure if you could use a Holley replacment TB, I think the throttle bores are large enough but the injectors are not. I have not done this. Good Luck.
     
  3. sled_dog

    sled_dog 1 ton status

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    454 has larger bores and injectors.
     
  4. jwduke

    jwduke 1/2 ton status

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    Check with "Summit Racing's" catalog, it list's the same part number for "Painless Wiring", for a Small block, and a big block with TBI. I think you will need to replace the prom in the computer, with one for a big block. Or you could have a custom one burned, for use with headers, cam, etc. Good luck!!!
     
  5. Thunder

    Thunder 3/4 ton status

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    The wireing harness in the 350 and the 454 TBI is the same except for the IAC valve wire. You can get an adapter that plugs right in cheap from turbocity.com
    You can use the same ECM but you will need the stock 454 Prom chip for your year truck and 2" bore TB.If you dont have them You can get these from turbocity also. They also burn custom chips and have other performance TBI mods.. /forums/images/graemlins/thumb.gif
     
  6. azblazor

    azblazor 1/2 ton status Premium Member

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    You'll need a stock 454TBI prom but make sure its for 91 or later to run the 4L80E. You'll need the BBC TBI unit. They are on ebay all the time - but you'll pay the better part of 200 for one on ebay. The distributer is the same on both. Wiring harness should be the same.
     
  7. afroman006

    afroman006 1/2 ton status

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    Its been awhile since I've looked at it but I think the Holley throttle body is only rated for up to like 350 HP? If it were me, I would go with one of Turbo City's tricked out throttle bodies. You send yours in as a core and they send you a completely refurbished badass one, thats the way I understand it to work, right? Anyway lemme know what you do as I am interested in this too.
     
  8. sled_dog

    sled_dog 1 ton status

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    I really want to get ahold of one of the Turbo City units. I have figured out I could easily replicate everything they do except the larger bore cheaply.
     
  9. themaddhatter

    themaddhatter Registered Member

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    Keep us informed of what you find. I have a 91 3/4 ton too that I may big block sooner then later /forums/images/graemlins/thumb.gif

    Don't want to have to reinvent the wheel
     
  10. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    I'm also trying to learn about this type of swap...

    Why would you need a different PROM? I figured the computer would see a signal from the O2 sensor and feed it appropriately. Does it actually know how much volume the engine is consuming?
     
  11. sled_dog

    sled_dog 1 ton status

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    they only adjust so much, after a point if your pulling that much the computer thinks something is really wrong. I wouldn't be surprised if it retarded timing or something liek that to try and fix the "problem".
     
  12. fortcollinsram

    fortcollinsram 1/2 ton status

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    Yeah, basically, the stock PROM is set up for a relatively narrow set of parameters as far as fuel tables are concerned...A BBC at idle requires quite a bit more fuel than a SBC to maintain the idle speed...If A SBC PROM is hooked up to a BBC, it will see the sensor reading at idle and will "look up" the corresponding amount of fuel to dump in the engine...A SBC prom just isn't programmed to handle the fuel requiremments of a 454...

    Basically, as long as the 454 ECM and the 350 ECM are similar (ie. no electronic trannies for both, or both fro TH-700's or TH-400's or 5-speeds...) the existing wiring harness will work, just swap the PROM or the entire ECM....

    Chris
     
  13. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    Aaahhhh... I see the light! Thanks for the good info fortcollinsram & sled dog! /forums/images/graemlins/thumb.gif
     
  14. ACannell

    ACannell 1/2 ton status

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    I'm in the process of doing the identical swap. Have you made any progress? As to the flywheel issue - does anyone know what fits the bbc (org. a sbc) to a 4l80e? By any chance does anyone know where to get a new one? My 454 is out of an 89' with a th400 and the new home is a v2500 w/4l80e. Thanks
     
  15. POORBOYK5

    POORBOYK5 Poor and homeless Premium Member GMOTM Winner

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    well this thread is from '03...:eek1: but a flexplate should be able to be bought for anything with overdrive (4l80e) with a 454 on or after '92(first year of 4l80e). I'm just not sure if they changed the balancing (internal or external) on the 454 by then. That would change the felxplate as well.
     
  16. blazin_blazer

    blazin_blazer 1/2 ton status

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    just like the OP, my buddys 91 2500 burb also had a 4l80e in it from gm, so 92 is not 1st yr of that trans. i'm looking at putting a 87 tbi 454 in my 85 k10. i think it will all swap over easilly since the 87 truck has th400, its ecm only controls the engine & my 85 has sm465.
     
  17. ACannell

    ACannell 1/2 ton status

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    It's been a while but flex plates no big deal! Turns out the stock OG FP from the 89' 454 has the same pattern for the torque converter. The TH400 & 4L80E share the same patterns. Yes the FP is externally balanced as well.

    I ran outa funds at the moment but I've made a little progress recently:) I gota a lift (all spring) for bout 100 bucks!
    [​IMG]

    [​IMG]
     

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