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Will a 8.1L work? What mods. need done?

Discussion in 'The Garage' started by Klef72K5, Dec 2, 2003.

  1. Klef72K5

    Klef72K5 1/2 ton status

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    Has anyone done this? I found a 8.1L from a 2000 truck with 9,000 miles on it. Will it bolt up to an 86 turbo 400? Can the computer be reprogramed to run without some of the sensors like the LT1? What would be a good price for a motor like this? It will be going in the 72 Blazer.
     
  2. dhdescender

    dhdescender 1/2 ton status

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    I'm damn sure it will bolt up. Those motors were bolted to 4L80E's If I'm not mistaken...and a 4L80E is the same as a TH400 as far as bellhousing goes.
     
  3. sled_dog

    sled_dog 1 ton status

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    there is a moderator over at www.bluetorchfab.com on their forum that is running a 4.8L small block from a new chevy in his Heep. I talked to him about it before, he is usually the completely stock motor and just had the computer reprogrammed. I pmed him for an email addy you can contact him at and talk to him about it. I'd love to put an 8.1L in a K5, or see it done, or any older GM.
     
  4. K5MONSTERCHEV

    K5MONSTERCHEV 1/2 ton status

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    We have a couple 8.1s at school, I had the same idea. Oh and a Duramax! Ill find something out for you. But first I have one quick question, would you be using the computer that goes with the engine and you want it to work with your tranny?
     
  5. 83ZZ502_Jimmy

    83ZZ502_Jimmy 1/2 ton status

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    It will bolt to your TH400, but.... /forums/images/graemlins/grin.gif

    The 8.1 has a drive by wire throttle setup. Meaning the computer controls a stepper motor to open and close the throttle body. May be difficult to fab this to work in your K5. ( got to get the pedal and associated electronics ) I did see in one of the big mags that they were able to use an LS1 TB with a regular cable. But reprogramming had to be done.

    Lastly, if this particular motor was coupled to the allsion, pretty much forget using the computer for anything. The two are VERY tied together. Find a motor from a manual tranny truck, it'll be easier.


    Hope it helps.. /forums/images/graemlins/tongue.gif

    John
     
  6. sled_dog

    sled_dog 1 ton status

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    email me at alan@1337info.com if you want that guys email address. Like I said hes running a 4.8L so hes got a place that can reprogram the computer to forget the transmission and all.
     
  7. Klef72K5

    Klef72K5 1/2 ton status

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    I'm not sure what tranny the motor was bolted up too. I would be using the computer that goes with the engine and I would like to use my TH400.
     
  8. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    This basic engine is derived from the 454-502 and will physically bolt to the transmission. You will have to work with e the electronics that are from the truck the engine came from. The intake mounting and everything changed so you couldn't put on a tbi intake or anything. Just checked at Arizona Speed and Marine, guy said good luck ( they sell turn key 8.1's for like 21 grand and up which sucks ).
     
  9. bigbluek20

    bigbluek20 1/2 ton status

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    I thought they changed the bellhousing patterns... 5.3/6.0 changed and the the 8.1 also changed it with the big block?

    I put a 96 Vortec 454 in my 82 K20 last year. Lots of work. I kept the 4L80E that was attached to the Vortec. I think you will need a transfer case with an electronic speed sensor regardless of tranny because the computer wants to know for adjusting emissions (90-91 NP241 worked for me, used speedo from same). I don't know of anyone that reprograms computers on these, but most sensors are pretty much on the engine except for the speed and Oxy sensors. There are some places that will at least reprogram the computer to get rid of the "key" code found on 98 and up computers (ignition key security thing).

    Wiring was almost a master's thesis project... okay, not hard, but definitely a lot of it... factory manual is a must for this.

    I think I gave $3500 for the engine and tranny with nearly everything (computer, harness, etc) with about 70k on it (from a rollover). Total cost was nearly $6k before I was done... cooling system, fuel system, electric fans /forums/images/graemlins/grin.gif, air intake, gm manuals, exhaust, etc. A lot was custom fabbed cheap, some could have been done cheaper, swapped the xfer case for free (traded the NP208). The salvage dealer at the time had just gotten in a 2wd 8.1/Allison... I think he was looking for close to $8k for that.

    One word, watch out for who removes it (if you don't do it yourself). Some will cut wires, leave stuff behind, etc. I was fortunate to have a guy very good with swaps... everything capped off, unplugged, etc. He even sent any little parts I was missing when I would phone him up. Little things like throttle cables, hoses, etc. can really eat you up.

    Biggest problem point... fuel system. Go in-tank pump if you can. I swapped 3 fuel pumps along the side of I-70 in Denver (they always died an hour from home) before I ended up using pusher pumps in-tank to get fuel through the switch to the high pressure pump instead of sucking it up to that point. /forums/images/graemlins/1zhelp.gif

    Now, with it all done and working (after 3 lifters went out and I "had" to add a performance cam since I was that far into it /forums/images/graemlins/crazy.gif ) - oh yeah! /forums/images/graemlins/wink.gif
     
  10. 74kay5

    74kay5 1/2 ton status

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    I know this is an old post but I didn't want to start a new one. If anyone has any wiring questions try speartech.com if interested in a 4.8 5.3 6.0 8.1 swap. John will answer any questions you have regarding the electronics. He has done the wiring and programming for almost everthing out there.

    Also BigblueK20, could you send me a picture of your transmission mount?
    I'm also going with the 4L80E and could really use a good picture of a mount.
    blackdog76@pirate4x4.com
    Thanks
     
  11. beater_k20

    beater_k20 Banned

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    dont hold your breath waiting on a response from him. he hasnt been active here in over a year and a half. :rolleyes:
     
  12. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    Reeeealy?

    old post i know..
    We hooked an 8.1L to a th400. using the stock ECM. There is a seperate TCM for the allison tranny. if you disconnect it, it will throw codes though..
    And you have to grab the pedal assembly and BCM for the drive by wire setup. Just bolt in the pedal and its a done deal if you get everything wired up right.
    We successfully got it running with the stock harness and computer... just a LOT of research and schematic diagnosis. :thumb:
     

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