89 K3500 Big block replacement

Discussion in 'Engine Performance + Maintenance' started by Rktman, Mar 3, 2021.

  1. Rktman

    Rktman Newbie

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    Greetings gents,

    I recently purchased an 89 Chevy 1 ton 4x4 auto with a TBI 366 big block. Originally it was the 454 TBI and the prev. owner replaced it with the tall deck 366. He said he thought it spun a bearing so I may be replacing it once I get it running (fixing wires now due to rats/sitting a few years).

    What would be required to replace it with a small block carbed motor?
    Coincidentally, I bought a car project the same weekend that has a 330 hp 350 SBC from Jegs with less than 5k miles.
    Thanks.
     
  2. Schurkey

    Schurkey I'm Awesome

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    There's an entire sub forum devoted to carb-swapped trucks.
    https://www.gmt400.com/forums/lsx-carb-swaps.14/
    perhaps a moderator will move this thread.


    Shortest possible story:

    Rip out Fatblock, install small block with carb and non-computer-controlled distributor. Grab the small-block accessory brackets and accessories from a similar-year SBC GMT400 Treasure Yard vehicle. Maybe grab the exhaust system, too.

    Figure out how to connect throttle cable, and trans TV cable or electric kickdown to carb throttle lever or gas pedal, depending on transmission.

    Re-route fuel plumbing to carb. Reduce fuel pressure to 6-ish psi with a regulator. Run fuel pump from ignition switch and oil pressure switch, expect long cranking times. Or trick the computer into getting the fuel pump relay (and maybe the cruise control) working, too.

    Get rad hoses and heater hoses to suit the engine and the chassis.

    Reduce torsion bar ride-height adjustment, make sure headlights are aimed properly.





    I think it's silly to disable OEM fuel injection for a device that functions on the principle of "Suck and Hope".
     
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  3. Supercharged111

    Supercharged111 I'm Awesome

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    Suck and hope? I always heard it referred to as a calibrated air leak. The good news is OP the engine mounts bolt on and so will the trans so if you were sweating that you can stop now.
     
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  4. Erik the Awful

    Erik the Awful Supporting Member

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    Not so much. The fuel bowls retain the fuel for startup.
     
  5. Schurkey

    Schurkey I'm Awesome

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    That's nice if it actually works out that way.

    Plenty of folks cryin' about long cranking times because the bowls are empty, and the engine-driven pump doesn't fill it/them fast enough on other forums I participate in.

    Yes, small-bowl carbs like Q-Jets are more prone than Holleys.
     
  6. Supercharged111

    Supercharged111 I'm Awesome

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    So you're familiar with my dad's Monte?
     
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  7. LC2NLS6

    LC2NLS6 I'm Awesome

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    When it gets stupid cold, and haven't tuned the Holley Sniper EFI for it, at 0F I had long cranking times before I threw more cranking fueling at it.

    If it were me, I'd sell the project truck and tree fiddy, get a blue print or adk/BPE 454-496-598 short deck reman non peanut port (get L29 heads or better like brodix race rite with stock height exh ports) engine, slap on all the stock stuff as best as I could, a cam, and Holley sniper EFI.
     
  8. b454rat

    b454rat I'm Awesome

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    Don't need a TV cable if original tranny is used, turbo 400. Don't even really need the kick down wire, that goes thru the ECM. Truck will fire up fine even tho fuel pump might not pump right away. There is still fuel in the bowls in the carb and lines. By the time it fires, gas will be flowin'.
     
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  9. Rktman

    Rktman Newbie

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    Thanks for the replies. "Suck and Hope" sounds like a modern political slogan, lol.

    I'm currently trying to diagnose why the 366 wont run before I do any swapping.
    I would like to keep the TBI system even if I have to do the swap.
    The truck will start and run for a bit with a little gas added to the throttle body.
    The fuel pump is not working and several wires seem to be chewed by rats.
    The wire on the oil sending unit is missing, the gas gauge is stuck on full and there are 2-3 wires running near the alternator that affect the fuel gauge. I'm studying wiring diagrams now, but if anyone has a pic of their engine bay wiring on 454 it would sure help me figure out what the PO did right or wrong. Thanks
     
  10. Rktman

    Rktman Newbie

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    If I do replace the 366 with another big block, I have a set of heads from a 70 402 that I had rebuilt years ago but never got a chance to finish that project. Are those heads of any use for this project?
     

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