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GM HEI Ignition


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Original post by: Andrew Levy

Many of us have heard the down side of these modules as being limited

to 5000 rpm on an 8 cylinder eng. Actually these modules are not limited

by the operating frequency but rather the original coils were the limiting

factor. The original coils where mounted in the top of the distributor cap,

where the temperature is quite high. Also as the frequency increases

the amount of time for the primary winding to cool decreases, so the effect

is as the temp of the coil rises so does the resistance in the coil, which

decreases the output. This is why MSD claims that if you replace the coil

in the cap with there Blaster coil it will increase the max rpm to 6000.

This setup with a MSD blaster coil can work to 7500 rpm on a six cylinder



/ \

/ \

W\ ------------- /C

G\/ \/B

W= positive lead from the pickup C= negative side of the coil

G= negative lead from the pickup B= positive side of the coil

First, mount the mod to a piece of aluminum .060in - .125in thick. Make

sure that you use the silicone grease that comes with the mod. I typically

mount the mod to the bottom coil bracket bolt. The following wiring

directions are for 240 z models. There are two black with white tracer

wires. For convenience, I connect the short one to the + side of the coil.

Now connect the longer black and white wire with the green and white wire

to the mods terminal B. Then a wire is connected from the coils negative

terminal to modules C terminal.

Here are some tips for swapping the distributors. Before you remove the

old dist turn the engine to 10 degrees before TDC, make sure it is on the

compression stroke by observing the direction of the rotor, it should be

pointing at the number one spark plug lead. When installing the new dist,

turn the dist body so that the #1 spark plug lead is lined up with the rotor.

In both cases you may want to mark the distributor bodies with the

location of the number one spark lead, so that you don't have to keep

installing the cap to check for its location. If this is done the timing

should be set at approximately at 10 degrees BTDC, which should allow the

engine to be started so a timing light can be used.


Here are the details on the HEI ignition system that I'm running.

About three years ago I built a L28 for a friends 70.

I intially set it up with a MSD 6A and a 76 dist. After a month or so

the MSD failed. So in order to get the Z on the road again I went down to

the local autoparts store and got an HEI module, it cost about $25 dollars.

Went back to the hooked it up and realized that it worked every bit as good

as the MSD. I have used HEI mods. in many applications before, but never

compared them to other electronic ignitions.

Here are some benefits to this system. First, the stock

tachometer will work with out any extra devices. Second, they are sold

everywhere and only cost $20 - $30 dollars. Third, they seem to be more

reliable than the aftermarket ignitions.

The installation is quite easy and should cost less then

$100 dollars complete. The parts needed are a magnetic pickup \ reluctor

type of distributor, and a four pin HEI module (Standard ignition pn #

LX-101) or equivalent, no ballest resistor is needed.

First you need to determin the polarity of the wires going to the

distributors pickup. Some have a red and a green wire, the red is the

positive. If you have one with two green wires or you can't tell what

color they are you will need to test them. This can be done by rotating

the dist. shaft the same direction as it would be turned by the engine and

use a volt meter to establish the polarity. This system generaters AC

current so look for a positive reading when the raised portion is

approaching the pick up and negative when it departs. You could try to

establish the polarity by starting the engine and use a timinglight to

check each combination, the one that gives you the most retarded timing

should be correct.

Below is a drawing of a average HEI module, the letters refer

to the pins. I mounted the HEI mod. on a piece of aluminum , sheet .o6o"

thick which bolts to the fender via. the bottom coil bracket bolt.

Remove the factory ballest res. and locate the two black-white wires, short

and long and the green-white wire. The longer black-white wire will

connect to the positive side of the coil. The short black-white wire will

be connected to the green-white wire. A piece of 14-16 gauge wire will

need to be run from the positive side of the coil to pin B on the module.

Another piece of wire will need to be run from the coils negative to pin

C on the module. The positive wire from the distributors pickup connects to

pin W and the neg. from the dists. pu. connects to pin G. I connected a

ground wire from a dist. hold down bolt to the HEI bracket. Make sure

you use the silicone sealer that comes with the module between the

bracket and the mod. If the the module is not grounded well it will fail.


HEI module -> / \

/ W C \

/\ G / - - - - - - \ B /\

dist. + /\/ \ /\ - batt.

- +

This setup will not work with all coils. It works best with a MSD

blaster coil. You can mail order these coils from Summit and Jegs for

about $25. I have gotten distributors from wrecking yards for $25-$40

dollars. The distributors where used in datsun 810's and Zs. These dist.

are very reliable electrically, but not so mechanically. There is a

plastic cage that holds three, 3mm ball bearings half of the time it is

broken or the balls have pitted the the thin spring steel races. This only

effects the operation of the vaccum advance. I don't run vac. adv. with

S.U. carbs. So in this case you could solve this problem with epoxy.

Another solution is to replace the bearing and cage with bushings made of

brass bronze or teflon PTFE. I have also modified these dist. to use

torrington bearings.

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