GM 4 Pin HEI - theory?

My favorite DSII trigger- ignition module is the GM HEI partly for it's expanding dwell feature. Other recent HEI ignition discussions generated a question on it's theory of operation :

from the internet;
Another unique feature of HEI is a dwell period that responds to changes in engine speed. Identified as an expanding dwell, the saturation time of the coil is controlled by engine rpm. At idle, an HEI system will experience a dwell time of 10 to 15 degrees and will increase to 30 to 35 degrees by 2,500 to 3,000 rpm. The ignition now has the output when the engine needs it--at high speeds and under load.

QUESTION: IF the generic HEI module determines dwell by internal RPM counter/comparator, then there is a different dwell curve for SIX cylinder vs Eight cylinder operation?. Gotta' get out the old Tach and Dwell ...

have fun

https://www.summitracing.com/search/par ... i%20module

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The signal from the HEI and Duraspark reluctor is an AC sine wave. The HEI module typically adjusts dwell based on the rise/fall time of that wave, so in actuality it really doesn't know if it's installed on a 4-, 6-, 8-, or 12-cylinder engine or what rpm it's at. All it sees is that the wave is coming in at a certain rate and reacts accordingly. That feature is what allows dwell compensation regardless of cylinder count.

The module calculates dwell in milliseconds, not degrees, and will adjust and vary dwell accordingly for best coil saturation up to a max current limit based on the coil impedance not by rpm, but by how quickly it sees that AC sine wave. A V12 engine will have more firing events than a four banger at the same rpm, so the same module provides different dwell to each engine at the same rpm.

It's a must to use a good heat sink on the module. I found that screwing it to the inner fender is not optimal. Get a finned heat sink and use dielectric grease. Google "ACDelco 10474610" for the best one. It's usually under $15.

There are Marine versions of the HEI module that provide an advance curve based on rpm, and those have to be matched to the engine cylinder count.

... thanks for the reply and explanation, the HEI module responds better than I thought. The HEI with the DSII distributor and suitable coil is simple and a performance upgrade for most small block six setups. The new direct-fitting HEI distrbutors for six' should be as good or better but I haven't tried one yet.

What's the advantage of the big MSD type ignition boxes for most cars?.

have fun

MSD -6al
Multiple sparks up to 3000 rpm's, rpm limiter & is a capacitive discharge system. Plugs right into the DS11 with a MSD adapter harness.
But get your wallet out.

afaih - Ford DSII ignition module triggers do not use variable dwell with RPM.
last question:
... what is suitable and actual spec' coil for HEI/DSII setup. OEM DSII Ford 12V coils seem to work OK. Some coils state they require current limited ignition module which I presume includes the GM HEI . Aftermarket can look like repackaged GM HEI coils.

thanks again

The multiple spark ignitions have coil modules which cost money to make, and a dollar saved is a dollar earned. Detriot started the whole with Presolite and Chrysler moving to solid state ignition first. Ford was sued over the Autolite/Presolite purchase, and had to rework the Autolite system through Motorcraft. AMC used Presolite igntions, but then had to move to Ford ignitions


Through the 70's and 80's, the Big Four pumped money into white box suppliers like Autolite, Presolite and AC Delco Remy first up, and then decided to work on the Big Threes systems. Chrysler created the worldwide use of electronic igntion, and then Congress made them sell off the family silver to Email, Bosch and that's where Pertronix got there conversion kit from...all Chryslers hard work with Presolite.

AMC bought Ford ignition systems
GM invested in there own system
Chrylser basically did its owm thing with White box suppliers, then got its fingers burnt and there systems got copied snd used by the Japanese (Mitsubishi, Toyota, Nissan via Mitsubishi Aerospace, Desno, Hitachi, Bosch in Australian made Silent Shaft 2555 engines used a Ford, Holden and GM Holden J car igntion system which Hyundia and Toyo Kogyo [Mazda] copied).

It was all in bred stuff. The goal was to make a better, cheaper igntion that met the performance, emission and economy targets.

The coils primary and secondary Ohms resistance spec issue is there to condition the right kind of spark, at the right time, without spark saturation. Ford had

one coil type for the Red and Green strain relief Duraspark I, and
another for the yellow and Blue strain relief Duraspark II..

The Brown strain relief Duraspark III is the most advanced kind of rotator distributor system ever, it has an EECII or EECIII ecm computer to periodically manage a crank position sensor to dynamically control where spark happens. Each variant had different coils to suit the igntion type.

Not all igntions are ballested. Ballasted (resistor type) electronic igntion systems exist not to throttle back, or educe peak voltage as is mistankenly thought, but as a way to place load on the ignition system to drastically improve start up after the coil has heated up, and to reduce power consumption. Its like a quick light off catalyst, it effects a change on the the cold performance of an engine part. A catalyst converts heated gas into an oxidation reaction. A ballast resistor brings on a secondary voltage change by Ohms Law. It uses Ohms law to load the coil and get it working with reduced voltage, not as a means of reducing voltage to the coil all the time.

The Duraspark I remains, IMHO, the singularly best system ever for a rotator shaft ignition, in terms of fat spark, and it got used until a cheaper option was found.

The Duraspark II was a downgraded because the electronics suppliers found another way to get as good a result, with less cash. So the DS II was a cost benefit/Quality/rpice trade off igntion.


The HEI was designed to do what the DUI does so well...incorporate the igntions and control box and coil all on the engine to ease assembly line work, just like the ALDL link...it was all designed to save cash while quickly scrweing together Louis Chevies and Henry Fords in Motor City.


When GM or Ford change a ballast resitster value, and the primary and secondary KiloOhms resistance, they do so to optimise spark (quality) and cost (price).

When GM went in1984 to Direct fire distributorless ignition on the Buick 3.8 with an aggressive 48 degree total advance, it was to save cash to make power and economy gains. They changed the whole igntion system to reduce igntion coil spark saturation, and get the right kind of spark quality to help emissions, durability. Waste spark hit town in 1988 with the GM 3800 version. Its whole reason for being was to reduce spark saturation

See page 2 http://www.underhoodservice.com/servici ... engines/2/

If you test a coil with an ohmmeter, the test specs are 0.5 to 0.9 ohms for the primary terminals under the coil, and secondary resistance of 5,000 to 8,000 ohms at the high-voltage terminal.

Click to expand...

See how tiny the primary resitance is.0.5 to 0.9 ohms is very small compared to an HEI or DSII.

5,000 to 8,000 ohms secondary resistance is 5 to 8 K Ohms


MSD, DUI are all trying to get the best results from a stock kind of rotator distibutor.


Here is what happened in the interbred Australian Bosch based distributor, which was a centrifugal and vac advance Autolite 1969 351 Windsor base, used on 318 Chryslers and 253/308/304 GM Holdens, and then later on gutted powered by a EST module in Holdens for years.

The Ford version was called the Austrlian X-flow or Cleveland Duraspark, the GM Holden HEI, or the Chysler ELB. They used a coil with a specfic primary and secondary ohm resistance, and noted if it was ballast resistor equiped.

/viewtopic.php?f=3&t=75528

9-230-064-705 came out of a 3.3 or 4.1 auto falcon or TF Cortina high comp engine.
9-230-064-710 manual 3.3
9-230-064-711 4.1 auto
9-230-064-716 came out of a XE 4.1 auto

Specs are generally a coil with Primary Resistance of 0.45 Ohms, Secondary Resistance of 6.6 K Ohms, if its not ballasted.


from ADDO in April 21, 2003

viewtopic.php?f=3&t=4163

Distributor test:
Connect a volt meter & an LED test light to the blue/white wire on the ignition module.
Cranking over the engine should get a pulse through the volt meter and the LED light also pulsing. Distributor test is OK if it does so

Coil test:
Using an ohm meter check the primary terminals, should read 0.45 K Ohms. Check secondary terminals, reads: 6.6 K Ohms
Put timing light on lead running from coil to distributor, you should get strobe. If nothing, no strobe, then a reluctor problem. Should get same result when tested on all spark plugs.
Check with Volt meter on both terminals. Voltage should fluctuate and LED pulse.


The old Ford Falcon Ignition coil - XE 3/1982-9/1984 6 Cyl 4.1Liter was the same as the XD/XE and Aussie Ford Broco/f100/250/350 3/1979-2/1982 8 Cyl 302 C 4BBL and 351c 4bbl.




They were standard oil fitted coils by Bosch with codes like:-.

Bosch - 9220-061-444, 9220-061-445, 9220-061-448, 9220-061-449,
Bosch - 9220-061-451, 9220-061-453, 9220-061-455, 9220-061-460,
Bosch - 9220-061-461, 9220-061-462, 9220-061-465, 9220-061-466,
Bosch - 9220-061-480, 9220-061-483, 9220-061-485, 9220-061-600,
Bosch - 9220-061-601, 9220-061-603

http://apps.bosch.com.au/AAExtranet_Tec ... lspecs.pdf

They were replaced with this http://www.sparkshop.co.nz/Catalogue/Pr ... t/69MEC717

Click to expand...

Is it true that the GM HEI module likes a .5 primary resistance coil? What happens if I run a 1.8 primary resistance coil with no ballast resistor?

OpelGT+3point3":30r5vynu said:

Is it true that the GM HEI module likes a .5 primary resistance coil? What happens if I run a 1.8 primary resistance coil with no ballast resistor?

Click to expand...

Yes, true.
http://www.jalopyjournal.com/forum/thre ... st-6864753

from post#19 by HAMB Member GMC BUBBA

This discussion concerns the ignition coils used with the HEI.
I tested three coils this morning with the waveforms shown .

1- 0.5 ohm (oil filled) ignition coil. Unit ws single firing a 25,000 test plug and used as waveform shows 5.8 amps clipped with current limiting ( hence the flat spot at shut of of control) and used a preset time of 3.6 mili sec to get er done. This is a normal function of a properly working high energy ignition system. You can hear see and smell the energy ( and feel if your not careful)

2-1.5 ohm coil...... Unit still fires a 25 kv test plug but you can hear the difference in enegy, waveform shows a decrease in current to 3.0 amps . ( A new point ignition runs at this decreased level )

3-4.0 ohm coil, would no longer fire the test plug and using a standard plug spark was at 2,000 volts and 1.5 amps .....this one wouldnt owrk very well if at all!

Click to expand...

Examples of those are


Type 1. Less than 1 ohm coils are electronic controlled to hack the current. A non oil filled replacment is the S10 remote HEI coil (These coils are found on HEI engines with small caps [except inline 6's with large cap HEI with coil post], late 80's to 90's 350's, 4.3's and 2.5's mainly GMC and Chev trucks and vans. 2000 and up coils are usually 0.2 ohm). These are like the Chrysler Australia /Ford Australia/Mitsubishi Australia and GM Holden Australia coil's.



Type 2. NAPA IC12 https://www.napaonline.com/p/ECHIC12

2.1 ohms primary, 8.9 ohms secondary. For 6 or 12 volt systems, but is a nominal 1.5 ohms

Type 3 NAPA IC14 napa coil is. 3.25 ohms. https://www.napaonline.com/p/ECHIC14

You HAVE to use the spec coil as GM intended. Effectively, if you are using a higher resistance coil it means that you will be effectively running a 12v coil on a 9v feed when cranking, resulting in a much, much weaker spark. It drastically robs spark energy out of the circuit. The system uses Ohms law to load up the ciricuit on cranking, its not really a voltage throttle, its a load sensitive throttle which then allows the reduced voltage.

Using the wrong (higher) resistance coil means hard starting, and it eliminates the ignition running the way GM designed it.

I was not aware of these advantages. Good info I can see one of these on my Bronco. The Pertronix module has multi spark advertised at Summit.

Coil controversy

seems the TFI or:
the modern round, oil filed, standard duty (accell, pertronix, msd, napa, motorcraft) coils will work fine
as long as they have 2 or less ohms output (1 to .5 is best)?

Now the relay wiring is something else I'd like more clarity…
Using a 5 pin Bosch as example (seen on HABM on-line)
80 HEI "B"
87A positive coil terminal
30 10amp fuse, to battery

86 ground
85 keyed ign. switch ?

Finally - the DSII distrib. needs to B well grounded for this modification (also HEI w/heat sink/compound)? There is no ballast resistor wire needed?

All this holds less interest for me so I need to B careful and follow well. Also, alone same lines, I have lill understanding so reside in the "plug these components into ur system to have it wrk well" type of category.
"Here. hold this wire 4 me kid."
:shockin:
(dunce cap emoji)