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Discussion Starter · #1 ·
Answers to GRANT\'s ignition questions...

*Grant* asked,
*Well, wasn't this whole string a kick in the pants! Here I was thinking the whole world was bowing to the 'GM -HEI' bandwagon and now this. Are there any up-grades that could be done to the DuraSpark ignition on a bone stock '80 258 c.i. that are honest improvements?*

Grab the print button...
The 80 model 258 CID engine had the Motorcraft distributor in it, with a DuraSpark ignition module.

There was a mid year change in Ford ignitions in '80, so if they ask when the truck was built, so if you say '80 model, you have a 50/50 chance of getting the wrong stuff.

Use a distributor cap base, distributor cap, rotor & plug wires out of an '81 Ford F-150 pickup with a 300 CID Inline 6 cylinder engine. (around $45)
This will spread the terminals out, and get the rotor up off of the shaft, and allow you to make a real jump to a performance ignition module later if you want to.

If you still have the original coil, you might try a new premium coil. (around $20)
If you insist in moving to an aftermarket coil, try the Accel Super Stock coils, or my favorites, MSD coils. Stay with the stock size canister coils. Don't be fooled by those huge MEGA coils.

SPRINGS! Good news, Mustang springs, (Mr. Gasket P/N 925D) will put some life in that tired ignition curve! (This is the single major attraction of the GM HEI update)

A Ford DuraSpark module from the same pickup mentioned above will do for a replacement if needed.
A Ford distributor advance plate with pickup coil from the same pickup will work if yours goes south.

Hang a MSD 6A or MSD 6AL on that puppy for the ultimate upgrade! MSD will get the fire lit no matter what. I guarantee you that MSD won't treat you like Jacobs or DUI has some of the people here...

Is this answers to your questions?
If not, let me know,.... Aaron.

When a fool and a wise man argue, Onlookers can't tell the difference...

Re: Answers to GRANT\'s ignition questions...

dang, all of my secrets are not secret any more!/wwwthreads_images/icons/tongue.gif
Aaron is right though, i would never throw a dura spark distributor away, they are a good piece, it is just the module that lacks a little. the ford coils are good units, in fact i have seen more out of these than some accell coils. the msd box has a built in driver, so you can bypass the module (with a little work you can leave it in place for a backup), and have a system that is easier to work on than a hei and is perfectly legal in most states.


/wwwthreads_images/icons/smile.giflet it snow/wwwthreads_images/icons/smile.gif

6,870 Posts
Discussion Starter · #3 ·
Re: Answers to GRANT\'s ignition questions...

The biggest draw back of all of the so called HEI systems, meaning GM, Mopar, and Ford, is they are INDUCTIVE ignitions. Factory inductive ignition systems have spark durations around 100 micro seconds, and voltages at the plug around 2,500 to 7,500 volts, with pitiful amperage.

An MSD hooked to a Motorcraft distributor and coil is a killer system! Use the stock electronic ignition coil, and the thing just screams!
The MSD uses CAPACITIVE discharge to saturate the coil. It throws about 400 volts at the coil, and the coil output is HUGE!
For you guys in smog states, MSD 6A and MSD 6AL are both 50 state emissions legal upgrades.

The only two real ways to rate an ignition system is spark duration (the time the spark lasts) and the output. (duration being the most important)
Output has two parts, raw voltage (20,000 volts is plenty for anything street driven), and amperage.
Amperage lacks in some systems because they don't want to sell anything that can kill someone.
The MSD modules squeeze out around 30,000 (average) volts, at about 1,000 micro seconds (ten times the inductive ignition), with amperages that will make you toenails bleed!
The only draw back is you can't use those crappy little well type distributor caps Jeep was so fond of. You will have to go to one of the newer Ford tower style upgrades and plug wires if you intend on going capacitive discharge ignition (CDI) and having it work correctly.

Sorry GM HEI guys, To do a MSD correctly for the GM HEI, you need a coil adaptor to remove the coil from the cap, and a decent rotor to make the system work correctly. If you don't, you just make more red dust faster...

(HEI is an acronym for High Energy Ignition, just a generic term, and a misnomer to be sure in this comparison)

This replaces all of the ignition modules in all factory ignition systems, and for $131.00 solves all of your problems... except for advance curve ($4.00)....

CDI is the way to get into the 20th century, now it is the 21st......

Just thinking out loud,..... Aaron

When a fool and a wise man argue, Onlookers can't tell the difference...

Re: Answers to GRANT\'s ignition questions...

Ah, now THERES the stuff I was looking for!
Much Thanks

60 CJ5
80 CJ5

13,432 Posts
Re: Answers to GRANT\'s ignition questions...

OK, here's my thoughs on the GM HEI, Jacobs and MSD ignition systems as related to the 258ci engine:

I. First some specifics:

1. Any ignition coil requires a certain amount of time to build up enough energy (saturate) to produce a spark across the plug gap.

2. The faster an engine turns, the less time there is between sparks. The coil has less time to saturate. This time period affects the ability of the plug fire. The output of the ignition coil drops off with increase in RPM.

3. Several other factors:
a. Heat Build-up in the coil at higher RPM.
b. Heat Build-up in the ignition module at higher RPM.
c. Hall effect switch times decrease with RPM.
d. Higher compression requires a "Hotter" spark

4. The spark value is determined by:
a. Voltage to the coil
b. Delivered amperage.
c. Resistance in the cylinder.
d. Speed of the Coil saturation.

II. Jacobs Ignition Systems.

Dr. Jacobs has a Ph.D. in electronics and is not afraid to use it. His systems are the state of the art in electronics. Jacobs is on the "Bleeding Edge" of automotive ignition systems. The systems use modern sophisticated electronic modules to determine the resistance of multiple spark discharges through the well cycle and optimize the next spark to optimize the power of the spark to completely expend the plasma. It's dynamic, constantly changing.

Diagnostics are harder to do…. And parts and help is through Jacobs or their re-sellers. Some systems are 50 State Legal, some systems are off-road only….

Installation is harder, but your OEM ignition system can still be plugged back in if there is a failure.


MSD systems use less sophisticated electronics than Jacobs to fire multiple sparks of a set, specified power level, through out the dwell cycle. This produces a cleaner burn of the plasma, but not as optimized as Jacobs. It is a static system.

Because parts are simpler, and the design is stable, diagnostics is easier, parts are less expensive. Help is through MSD and it's resellers.

Some systems 50 State Legal, some systems off-road only…

Installation is much simpler than the Jacobs, and your OEM system can be restored quickly.


The coil is located in the rotor cap. This reduces power loss delivered to the plug. The coil is powered at the full 12 supply voltage, rather than the switched 8+ voltage of the stock FOMOCO. This helps to produce the "hotter" spark. Also, the GM HEI module is a fast switching module, so that it will help the coil to fully saturate at higher RPM's. These are the two reasons that the stock GM HEI is an improvement over the stock FOMOCO system. The faster the module and coil react (pardon the electronics pun) the faster, and the "hotter" the spark produced. The system is capable of producing spraks of up to 90,000 volts, but I suspect that 45,000 to 60,000 volts would be more of a constant.

The next issue is hystersis and eddy current build up and heat dissapation in the coil. Here is where I wish I had some good information, but I can't find any… so I can only "trust" the GM engineers have factored in these problems. Pre-mature coil death would be the result from poor GM engineering.

The Distributor curve can be modified by using a differing advance springs, advance spring plates and or, installing the further after-market Crane Advance Kit. So, if you have the desire, or need to play… you can. Also, faster ignition modules and coils are available through many after-market sources if you want to "soup up" this system… just do your homework.

Now is the system 50 State emissions legal? Not on your life! You'd better do your homework if you want to run this DYI system on the street.

Is it easy to do? Yes.
It is costly? Depends on where you get your parts!

Is it dependable? I'd never heard a discouraging word about the GM HEI swap until Aaron offered his information. However, as a stock swap, parts are inexpensive, and readily available and diagnostics is fairly simple. The system can be understood by most shade-tree mechanics. The parts are not so sophisticated the prices start to climb. Can the OEM FOMOCO system be operated as a twin system? No, because you are replacing your distributor it would be silly. However you can run the OEM FOMOCO ignition module in unison to pulse the OEM TAC. It's not a bad idea to keep spare individual GM HEI parts, ignition module, etc. or the OEM FOMOCO distributor in a take along parts box.

So far, excluding wiring questions, the GM HEI delivers improved performance for a low price, off the shelf, easy to retro-fit ignition system.

This system has been used for several years on Toyota's, Ford's as well as retrofitted to several European autos and older GM engines. It's reliable enough that other companies, including MSD, make improved versions of this system and sell them at a substancial profit.


IMHO if you want to get a "prescription" ignition upgrade go with MSD or Jacobs. Each of these systems, Jacobs and MSD are fine ignitions systems. They each solve a problem in unique ways.

However, if you want an "over the counter" ignition upgrade, then look at the GM HEI. In any case, you will get what you pay for. I've run the FOMOCO system and now have the GM HEI (Thanks to Larry Maggio... he's a real MENCH!)... am I satasified with it? You bet I am, in fact I'm so pleased with the GM HEI that I sent my FOMOCO distributor to Dutchjeeper in the UK.

Good Jeepin'


6,394 Posts
Re: Answers to GRANT\'s ignition questions...

/wwwthreads_images/icons/tongue.gif My personal view on all this is that an upgrade should be only a step away from stock IF POSSIBLE. The GM HEI is desireable because it is common as dirt, HOWEVER, it does require carrying a second complete distributor or a second bottom end to get going again if the modified Jeep/GM snaps off from a severe shock load, or otherwise fails, The repair parts, though are super-plentiful and you can crawl through the brambles to an old farmyard and lift one in the night if need be. Again, the BIG problem is the stem for the V8 application. I worry about how small it is. The FORD/JEEP conversion using the MSD box seems to have satisfactory if not OUTSTANDING spark characteristics. It will also work with the stock coil and the stock distributor., AND plug back into the original, common-as-dirt Ford/Jeep module. The Ford parts are plentiful and easy to steal in the end times when Janet Reno's Klintun-Gore gestapo are trying to run you down and take your Jeep and guns. So from a pure reliability standpoint, there are fewer NON-AVAILABLE in-the-middle-of-the-night-and-hard-to-work-around items on the Ford conversion than on the GM HEI. I like the GM HEI systems, but they do have a problem with arcing inside, and if you broke the specially made GM/Jeep stem, you're really stuck. We are going with the Ford conversion, and with an MSD6A backed up by a stock Dura-Spark module on the SNOJEEP; we feel that combination has the best reliability and performance combination of all the systems available. They'll never catch us! We gots MSD!!/wwwthreads_images/icons/smile.gif

I never believe any statistics unless my moonguys /wwwthreads_images/icons/crazy.gif/wwwthreads_images/icons/wink.gif made 'em up themselves.
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