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Thread: How to Upgrade to High Energy Ignition (HEI)

  1. #1

    How to Upgrade to High Energy Ignition (HEI)

    HEI was industry standard when DeLoreans were new in the showroom, especially among American and Japanese manufacturers:

    SparkPlugGapComparison.jpg

    If you want to upgrade your DeLorean to those same standards, here's how to do it.

    Three things are necessary for HEI:
    1) Suitable coil (Bosch blue coil is not suitable)
    2) Increased voltage into the coil
    3) Widened spark plug gap
    If you omit any of these three requirements you won't have HEI (or at least not for long in the case of a Bosch blue coil).

    ------------------------------------------------------------------------------------------------

    Step 1: Replace the Bosch blue coil with a coil suitable for HEI. *** THE BOSCH BLUE COIL CAN NOT HANDLE HEI ***

    I am running a Pertronix 40,000 volt flamethrower (retail about $40):

    HEI_HowTo_1.jpg

    Remember that coil voltage rating is only its potential output. Without Steps 2 and 3 the coil will continue to produce lower secondary ignition voltages despite its potential to do better. Simply throwing an HEI coil on the car alone does *NOT* produce HEI.

    Do *NOT* use the coil label to position and wire the coil -- use the "+" and "-" markings on top:

    HEI_HowTo_2.jpg

    This means your label may well end up facing the firewall, as mine does. If you position and wire the coil by the label alone, you may end up wiring the coil backwards. I have had to correct this error on other owners' cars. Bosch blue coils often are marked with numbers instead of polarity signs, which has confused owners. In such instance "15" is positive and "1" is negative.

    Bottom line: White/Yellow wire goes to the positive terminal, White/Slate (Gray) goes to the negative terminal.

    ------------------------------------------------------------------------------------------------

    Step 2: Increase voltage into the coil.

    *** Do not do this unless you have upgraded to an HEI coil. Bosch blue coils can not handle increased voltage ***

    There are three ways to increase voltage into the coil using the stock resistor grid:
    1) Use one resistor (yields about 11.5 volts into the coil)
    2) Use both resistors in parallel (yields about 12.5 volts into the coil)
    3) Bypass the resistor grid altogether (yields about 13.5 volts into the coil)

    One resistor:

    This is what one active resistor active looks like:

    HEI_HowTo_3.jpg

    Resistance is ~1 ohm:

    HEI_HowTo_4.jpg

    Yields ~11.5 volts into the coil (alternator charging):

    HEI_HowTo_5.jpg

    Two resistors *IN PARALLEL*:

    This is what two resistors *IN PARALLEL* looks like (note the jumper -- both terminals have to be tied together to cut resistance in half):

    HEI_HowTo_6.jpg

    Resistance is ~.5 ohms:

    HEI_HowTo_7.jpg

    Yields ~12.5 volts into the coil (alternator charging):

    HEI_HowTo_8.jpg

    Resistor grid bypassed:

    To bypass the resistor grid altogether, connect White and White/Yellow wires together. Resistance will be zero, and voltage into the coil will be full charging voltage (~13.5 volts).

    ------------------------------------------------------------------------------------------------

    Step 3: Widen spark plug gaps

    Spark plug gaps act as a voltage regulator. As soon as a spark jumps its gap, that is the maximum amount of voltage the coil will discharge. Even if you have an HEI coil and increased voltage into it, if spark plug gaps are too small, secondary ignition voltages will remain low.

    I am currently running Autolite 103's gapped .046":

    HEI_HowTo_9.jpg

    Multi electrode plugs are virtually impossible to regap -- just buy a quality set of single electrode plugs and gap them approximately .05".

    ------------------------------------------------------------------------------------------------

    That's it. The only new components necessary for HEI are a suitable coil and a crimp on electrical terminal or two. The stock ignition ECU can drive HEI no problem. I ran one for about half a decade, and quite a few owners are still running one to this day. Ignition ECU can be swapped out of course, but that is optional, not mandatory.

    This is a schematic overview of my own ignition:

    HEI_Schematic.jpg

    It has a few additional whistles and bells, such as a fuse link into the circuit (original circuit is unprotected, despite the fact that almost the entire car is grounded through the metal bracket that holds the coil...) and real wire plug wires, but those are optional, not mandatory. I also am running a Ford ignition module, simply because a DeLorean runs better as its ratio of Ford components increases:

    DurasparkECU.jpg

    Bill Robertson
    #5939

  2. #2
    Devout Follower Of He Who Walks Behind The Rows NightFlyer's Avatar
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    This is a great write-up!

    Thanks Bill!
    "Driving Concours - proving it's possible with every mile!"

    --Josh S.
    #1798

  3. #3
    Somebody in a position of power needs to correct the typo in the thread title (I'm just a peon).

    Bill Robertson
    #5939

  4. #4
    Devout Follower Of He Who Walks Behind The Rows NightFlyer's Avatar
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    Sorry I missed that. It's done
    "Driving Concours - proving it's possible with every mile!"

    --Josh S.
    #1798

  5. #5
    Senior Member
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    Thanks!! Might be a good winter project!
    Patrick C.
    VIN 1880
    A video of my modifications can be seen here: https://www.youtube.com/watch?v=_yUpusPAvJc

  6. #6
    Doesn't have to wait until winter: upgrade only takes 10-15 minutes -- however long to rearrange the resistor grid, stick a new coil in, and widen the spark plugs.

    Bill Robertson
    #5939

  7. #7
    Senior Member
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    Probably a dumb question, but would this mod put more strain on the pickup coil in the distributor? Maybe wear it out quicker with the higher voltage?
    Patrick C.
    VIN 1880
    A video of my modifications can be seen here: https://www.youtube.com/watch?v=_yUpusPAvJc

  8. #8
    Hall effect sensor in the distributor never sees secondary voltage. All it does is return a signal from the ignition ECU (ECU never sees secondary voltage either -- only coil input voltage). Only change is from the coil south. ECU wiring is a totally different circuit (except for grounding the coil of course).

    BTW: HEI works just fine with the stock Bosch ignition ECU.

    Bill Robertson
    #5939
    Last edited by Greasy DeLorean Mechanic; 02-26-2014 at 07:44 PM.

  9. #9
    Just Plain Nuts Lou and "Boo"'s Avatar
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    I wonder if my resistor is bypassed or if I'm running HEI with one hooked up, I'll have to snap a picture tomorrow and post it here to show you.
    Lou and "Boo" - The man you love to hate.

    Boo- The car you love to hate.

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    "Boo"-VIN 5835
    'Fastest naturally aspirated PRV'
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    "Blue"-1985 Fiero GT
    3800sc swap

  10. #10
    Senior Member
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    Thanks, Bill. By the way, where did you get your really good spark plug wires I've read about before?
    Patrick C.
    VIN 1880
    A video of my modifications can be seen here: https://www.youtube.com/watch?v=_yUpusPAvJc

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