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swapping from tbi to carbuerated in 91 silverado

Discussion in 'The Garage' started by swampynthrcecort, Sep 30, 2006.

  1. swampynthrcecort

    swampynthrcecort Registered Member

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    I am currently debating on replacing my stock tbi 350 in my 1991 silverado w/ a carbuerated 454. I have a built 700R4 but I am poorly informed about the connections between my tranny, computer, and engine. Will replacing the fuel injected 350 w/ the carbuerated 454 screw with my computer/gauges etc? Or will it be an easy swap w/ little to do but remove some excess wiring harness and move some engine mounts? Any help would be greatly appreciated.
     
  2. JEBSR

    JEBSR 1/2 ton status

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    Leave the mounts where they are. Your 700r4 is not computer controlled, the only thing electric on it is the lock-up converter. So get behind your glove box and disconect and remove the computer, then pop the firewall plug (that the wiring goes through) out and pull the harness out and lay it on top of the engine and that's all the wiring you need to remove. You can leave it in if you want to but it just gets confusing that way if you ask me. Swap all your temp and oil pressure switches onto the new engine and then just plug them back up and your good to go. I do believe you will have to get an aftermarket setup to make your converter lock on that 700 though. Someone else should chime in that knows for sure though.
     
  3. swampynthrcecort

    swampynthrcecort Registered Member

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    Thanks jebsr for the help, i hate going into things blind, this eases my troubles considerably
     
  4. sweetk30

    sweetk30 professional hooker Premium Member

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    could get a 454 tbi or holley tbi and a 454 computer/chip. then add a 4barrel to tbi adaptor and keep the 454 and have tbi .
     
  5. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Couple things come to mind with regards to this swap.

    First is the fuel system. Your TBI runs a 12 psi in-tank fuel pump, that has the fuel lines coming up at the back driver's side of the intake. You'll either need to re-route the lines to come up to the stock fuel pump on the pass front side of the engine and remove the fuel pump, replacing it with a peice of hose, or re-route the lines to your carb, and install a 5 psi fuel pump into the tank.

    Next up is cooling. The 454 might need a bigger rad than what your truck has right now. I know 454s were available stock, but I am not sure if they got a different core support or if the 454 rad would bolt right in.

    The 700r4 should bolt straight up, assuming you've got a flexplate that is compatable with the torque converter's bolt pattern. Tranny will be fine so long as you get a TCC lockup kit. You can find a stock one from any 84ish - 86 truck that has a 700r4. Pull the whole thing, and it should bolt straight up less needing to figure out the brake switch (you want one that kills the power to the switch when you hit the brake, I do believe that those trucks are equipped with one stock) and changing the connector for hooking up the positive terminal.

    Confirm that the lockup is working, go for a quick drive, and get up to about 60 mph. Without letting go of the gas, press the brake with your left foot and see if the engine revs up. Also find a reasonably steep hill, and accelerate up it to see if it shifts out of lockup. The engine should rev up, but not shift back to 3rd. You can confirm you just unlocked rather than downshifting by forcing the shift back to 3rd, and seeing if you pick up any rpms.

    Wiring should be pretty simple. As mentioned above, take the glove box out, unhood the under-dash connector, and ECM, then pull the wiring through the firewall, and unhook everything from the engine. There will be a few wires that are AC related, or head to the fuel pump, seperate them from the rest of the harness, but don't cut them.

    Once all the basic TBI wiring is out, you should be left with the standard starter wires, gauge sending unit wires, and power wires for the ignition. You'll want to take the thick red wire that goes to the coil stock, and put that on the batt term of the HEI cap, and if the truck has a tach, move the white wire from the coil to the HEI cap. You'll also need to take the sending units from the old engine, and bolt them onto the new one. They should hook right up. If you arn't using the electric fuel pump, you can cut it's wire, and remove the oil pressure switch (not sending unit).

    All your gauges should work fine, as the speedometer is run off the transmission, and you'll have just swapped the rest of the sending units over.
     
  6. 1985_K5_Silverado

    1985_K5_Silverado 1/2 ton status

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    Definitely, if the TBI is already working on the 350, do the work and eat the initial expense to make the TBI work on the 454.
     
  7. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    If you wanna go the EFI route, make sure you put in a camshaft that is EFI friendly... Sucks having to try and tune up a TBI setup on an engine that isn't built to make the job easier :)
     
  8. swampynthrcecort

    swampynthrcecort Registered Member

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    I have thought about going the TBI route, but my main obstacles are budget and a possible marriage date coming up. Carbuerated just seems more cost effective right now, maybe i'll just roll up all the TBI wiring and keep it around for later
     

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