Distributor: HEI Conversion

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Distributor: HEI Conversion

Distributor: HEI conversion

Time: 2 hours

Tools: standard wrench set, flat-blade and/or Phillips screwdriver, wire strippers/crimpers

Cost: varies by manufacturer- approximately $175-$400

Tinware: HEI distributor (new, rebuilt, or used), HEI ignition lead connector, HEI style plug wires

Tip: Label or mark the location of your spark plug wires on the distributor cap for fast, easy reference.

Tip: When you have installed your HEI distributor, its best to widen the plug gap as well.

Tip: You should run a new power wire that is getting a full 12 volts. Simply splicing into the existing lead is not getting maximum power to the ignition, as that is a resistance wire. If you measure the juice at idle on that wire, you will find it to be only around 9 volts. The car will run and operate using this wire under normal driving conditions, but the power loss will be noticeable at full throttle.

Performance gains: increased coil saturation, higher spark output, more reliable performance

The vast majority of cars produced through the sixties and early seventies were all factory-equipped with a points type ignition. Although not likely to be considered the greatest manager of spark, at the time there was no other option. It was not until the model year of 1974 that GM offered the new HEI ignition system as an alternative. One year later in ’75, it became standard equipment for all, and with good reason.

The GM HEI, which stands for High Energy Ignition, is a breakerless, transistor- controlled, inductive discharge system. It operates in a similar fashion to the conventional points type ignition, but relies solely on a series of electronic signals to turn on and off the primary current rather than the mechanical opening and closing of points. This task is routinely carried out by the switching transistor- located inside the ignition module. In fact, the HEI distributor is responsible for housing all of its components in one highly self-contained unit. In addition to the module, you will find the ignition coil, the pick-up coil, the magnetic pick-up assembly, and the mechanical and vacuum advance units– all nestled tightly under the cap.

I would bet that anyone owning or driving one of these older, pre-HEI system equipped vehicles, at one time or another has run into problems with their stock ignition systems. Let’s face it; points are not our friends. No matter what you drive or the application, they always seem to be in a constant state of tune, looking for that elusive (if not imaginary), sweet spot.

With so many other performance improvements that can be made on your car, who wants to spend their time adjusting the dwell angle? Sure, electronic ignitions such as the HEI are a little more expensive than the “rebuilt special” at your local parts store. However, in the long run, the time and headaches you spare fiddling with your ignition will more than make up for the initial deficit of purchasing a new one.

By simply switching over to an electronic distributor, not only do you eliminate the aforementioned hassles of points, but you will also notice a significant increase in your car’s overall performance. From crisper, off-idle throttle response to extra top end pulling power, the gains to be had by merely removing and replacing your stock distributor with a high performance HEI are downright impressive.

And so, this brings us to the garage. Anytime you pull the distributor out of the motor, it’s important to make note of a couple key elements prior to removal. First off, detach the spark plug wires and the coil wire, and then remove the cap. Before loosening the distributor clamp and allowing the housing to rotate, mark the position of the housing as well as the vacuum advance unit and the rotor, all in relation to the engine block. Loosen the clamp and lightly lift up on the housing.

After removing the ignition coil and leads as well as the plug wires, the distributor is now ready to come out.

If the motor is undisturbed while the distributor is out, it’s simply a matter of reversal at this point to install the new HEI unit. Realign your markings and let it fall into place. DO NOT force it! The teeth of the gears must properly mesh together in order to fully reseat. Once in position, hand-tighten the single bolt and clamp to allow for slight adjustability when re-starting the motor.

On the other hand, if the motor has been moved, you will need to locate its TDC (top dead center). One easy way to do this without removing the valve covers is to pull the No. 1 spark plug. Place a finger over the hole and rotate the engine by hand until the compression is felt. When the timing mark on the crankshaft pulley matches up with the “0” on the timing tab, you have reached TDC. Now install the distributor with the rotor pointing at the No. 1 terminal on the cap.

When reconnecting the new unit, you will need to purchase and splice in a single HEI terminal connector. This is your “hot” ignition wire coming from the engine harness.

With the ignition coil neatly tucked inside the HEI, it makes the electrical hook-up a cinch. All you need to do here is splice the HEI connector into your existing “hot” ignition lead. For better performance, see Tips at beginning of this article. The connector then plugs into the cap at the “BATT” terminal. If you run an aftermarket tachometer, a second connector will be needed. It plugs in adjacent to the ignition lead at the “TACH” terminal. As I am sure you know by now, points type spark plug wires are not interchangeable with an HEI cap, and vice versa.

What a night and day difference between the two! The HEI distributor actually houses the ignition coil underneath that massive cap.

You will need to purchase a new set to match your new distributor. With that said, reattach your individual plug wires to their proper posts. Take your time and make sure you have them right.

With everything finally back together, reconnect the negative battery cable and fire up the engine. Proceed to set the timing, and secure the hold down clamp. It’s a good idea to recheck the timing once more to ensure the housing did not move while tightening.




  1. When you have installed your HEI distributor its best to widen the plug gap as well.

  2. Shannon Born says:

    I agree on the wider plug gap. I run mine at .045. One mistake in this article….you do need to run a new power wire that is getting a full 12 volts. Simply splicing into the existing lead is not getting full power to the ignition, as that is a resistance wire. If you measure the juice at idle on that wire you will find it to be only around 9 volts. Yes, the car will run and operate using this wire under normal driving but the power loss will be noticeable at full throttle.

  3. Good points, thank you!

  4. herbert jones says:

    a question where would you run this wire from?

    • Use the original power wire to energize a (weather-sealed) relay of sufficient capacity… even the inexpensive relays are good enough as you’ll need less than 10 amps at 12vdc. For power to the distro itself, use direct battery power (for the full 12v +).

  5. Christian Swenson says:

    You have to get the oil pump tang to engage by pushing down on the dist and cranking motor.
    Shear luck if it just drops in.
    Also, you need to get the base timing set with the vaccum disabled and be sure to verify a full 32 degrees of mechanical advance.
    Then try adding the vac in for low load driving.
    Timing is everything and a race engine shop can make a huge difference.
    EVERY engine requires its own timing and mixture now that all the fuel is being burned with the hotter spark!

  6. You don’t discuss that most HEI’s do not have a mechanical drive for the tach. You need to have a conversion for this or purchase an HEI module that supports your mechanical tach. I have a 69 Vette that has Delco HEI and it works great but my tach doesn’t so I picked up an older distributor with a Mallory electronic ignition module that solves the problem.

  7. james chapman says:

    can spark plugs wires be tied together or should stand off be used.

  8. Are there clearance issues with a cowl induction air cleaner (1st Generation F-Body).

  9. Charlie Conser says:

    I cringed at the sight of the open intake manifold in the top photo. Through some painfully gained experience of having to open a race engine in a motel parking lot, I would recommend that the top of the manifold always be covered whenever the carburetor is removed, even if only with a few strips of duct tape. Keeping around a used gasket that has been taped over is a handy choice. While not exactly on the primary subject of this article, illustrations showing practices that should be avoided send the wrong message.

  10. Question, what do you do with the wire from the starter solenoid that supplies power during cranking, just connect it with the other wire?

  11. I ran a relay off the alternator post and trigger wire hooked up to energized wire in harness with it being live having key on. Works great. Ran poorly on the resistance wire. Confirm connections are tight and also voltage with multi tester. Rock and roll.

  12. Tom Whitacre says:

    Get 12 volts from Fuse box in side car spade terminal marked switch (Ign) . Most 60,s gm cars have it be sure to check it with test light ( key on key off )

  13. kurt hansen says:

    also you will need to change your Ignition shielding around your new distributor to a 75 and newer ign. shielding because of the bigger cap if you want to keep the shieling covering your distributor

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