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Thread: HEI and TBI

  1. #1

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    HEI and TBI

    Some noob questions here.

    Im getting ready to unpgrade my ignition system with the GM HEI. I read a few things regaurding the HEI and other upgrades, they may not work together.

    Im looking to ditch the carb and go with the Howell TBI kit but I have read that the HEI will not work with FI. Is this true?

    Also will I need to preform the nutter bypass in my 360 for the HEI to work properly?

    Thanks guys,
    Sorry for the basic questions.

    Josh

  2. #2
    Thank you from BT ULTIMUS MAXIMUS STATUS tufcj's Avatar
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    Since the Howell system is GM based, they can make it work with the HEI as long as you order the wiring harness from them and tell them that you're using HEI when you order it.

    Since the HEI wasn't available when I bought my Howell kit, I didn't get it. I can still use a HEI, but it won't have the computer controlled advance. The HEI is a simple 1 wire hookup, just run the hot wire that goes to your coil now to the + connection on the HEI unit.

    Bob
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  3. #3

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    So the Howell TBI will work with the HEI. Good to know

    Does anyone know about the nutter bypass and if it needs to be done for the HEI to work properly?

  4. #4
    Thank you from BT ULTIMUS MAXIMUS STATUS tufcj's Avatar
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    I've got the schematic for the nutter bypass, but I have no idea if it's needed for HEI conversion.

    Bob
    tufcj
    1969 AMX
    1966 Rambler Rogue

    If you need a tool and don't buy it...
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  5. #5

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    Yea I have the Schematic too but thanks...

    One more question

    Whats the diffrence between DUI and HEI?

  6. #6
    Quote Originally Posted by JFlanny11
    Yea I have the Schematic too but thanks...

    One more question

    Whats the diffrence between DUI and HEI?
    DUI (Davis Unified Ignition) is a company that makes and adapts HEI style ignition systems for all sorts of engines.


    As far as your original question, most HEI distributors that are converted to the AMC engines are the basic, non fuel injection distributors.

    First, a little history:

    GM came out with HEI a long time before any kind of electrical fuel injection. It started as a self contained unit that didn't require an external ignition module. All the parts fit under the distributor cap and the coil mounted on the top. The internal module is a 4 pin unit that connects two pins to the magnetic pickup and 2 pins to the coil (which also connects to the battery, giving the module the electricity it needs). This worked fine until GM wanted to use the computer to control the spark timing.

    When throttle body injection came along, GM made a modification to the HEI system by adding more pins to the module and adding another connector that hangs out of the distributor. Basically what they did was to route the pickup signal to the computer and have the computer send a signal back telling the distributor when to fire. They locked out the advance (both mechanical and vacuum) so that the distributor would always stay at zero degrees of timing. The computer would wait a few degrees before telling the module to fire the coil, giving it full control over timing advance. For that, you have a 7 pin module that fits in the traditional large cap HEI distributor. They also decided to make a smaller HEI distributor to fit other stuff (like the TPI manifold on the Camaro/Corvette V8 ) and use an 8 pin module (7 pin with a ground pin instead of grounding with the mounting screw) that connects to an external coil.

    Here's some more information on the various types of modules: http://www.megamanual.com/ms2/GM_7pinHEI.htm


    When it comes to HEI on non GM engines, most manufacturers only make the old style 4 pin HEI distributors and not the 7 pin fuel injection compatible distributors. The reason being that most people who convert to HEI are not trying to add GM fuel injection to a non GM engine. They're usually running carburetors or not bothering with spark control in their fuel injection conversion.



    If you want to run computer controlled spark with your TBI conversion, you need to do one of a couple of things.

    1. Find a TBI compatible HEI distributor from a GM engine and have it machined to fit your engine. You need a shop with a qualified machinist to do this for you (unless you are a qualified machinist). Hook it up like you would on the GM engine. One power wire, one plug to the computer (and, if it's a small cap, one plug to the coil).

    2. Get a magnetic pickup distributor that works on your engine. The stock motorcraft would work, so would an aftermarket distributor. Lock out the mechanical and vacuum advance. Connect the distributor directly to a 7 or 8 pin HEI module that you mount in a weather tight box (like the inside of a gutted out motorcraft box). Connect that module to the computer and to your coil.

    No matter which option you choose, you disconnect everything else from your factory ignition which makes the nutter bypass irrelevant.


    If you just want to plug in a standard 4 pin HEI ignition, all you need is a power wire. Everything else can be disconnected.
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  7. #7

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    bypass

    If you install a HEI ignition you won,t need the old coil, the ignition box or the extra feet of wires and the computer that controlled the carb. Just one keyed source hot wire to the coil. I might be wrong but the nutter bypass was orig for the 258 6 with the computer controlled Carter carb with the stepper motor, it basically got rid of all that.
    84 CJ 7 304, Arb rear, 35 BFG,s with a 2 1/2 spring lift only and to many other mods to list, plus a offroad trailer also on 35 BFG,s

  8. #8
    Thank you from BT ULTIMUS MAXIMUS STATUS
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    thats is what the nutter bypass is for. did that on the eagle.
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  9. #9

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    HEI

    Forgot to mention, if you buy the HEI on E Bay make sure you run a ground wire from the coil to the engine, on my 304 there was no spark and it drove me crazy for a few minutes till I realized that it had no ground, I thought that it would ground through the distrib body but it didn,t.
    84 CJ 7 304, Arb rear, 35 BFG,s with a 2 1/2 spring lift only and to many other mods to list, plus a offroad trailer also on 35 BFG,s

  10. #10

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    Re: bypass

    Quote Originally Posted by hugh
    If you install a HEI ignition you won,t need the old coil, the ignition box or the extra feet of wires and the computer that controlled the carb. Just one keyed source hot wire to the coil. I might be wrong but the nutter bypass was orig for the 258 6 with the computer controlled Carter carb with the stepper motor, it basically got rid of all that.
    You are correct. The Nutter is just for the Carter carbs and I6 258.
    You can take out all of those wires and that pesky controller.
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