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Discussion Starter · #1 ·
Answer for LEVE\'s ignition questions...(LONG)

Pretty good reading, and a fair analysis of what's going on. You have a good grasp, but I don't agree with some of your conclusions....
(here is where it gets long.... so the easily put to sleep take notice...)
Keep in mind here that the questions I have been responding to are for street driven vehicles that will not normally see 3,500 RPM in service.
LEVE's comments in *---*

*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.*

That is a law of physics. I don't think anyone will think of a way around that one...
*2. The faster an engine turns, the less time there is between sparks. The coil has less time to saturate.*

Another law of nature. I still agree.
*This time period affects the ability of the plug fire.*

The plug doesn't 'FIRE', it simply provides an air gap, that if everything goes correctly, the spark energy makes it here in sufficient volume to jump that gap.
It's a small mistake, but you were trying to be exact in your stamens, and I thought it should be corrected.
*The output of the ignition coil drops off with increase in RPM.*

Not necessarily true. It would depend on the ignition type, and the maximum RPM of the engine. A capacitive discharge ignition would see no noticeable decrease in spark energy because of the ultra fast saturation times on an engine driven on the street.
*3. Several other factors:*
*a. Heat Build-up in the coil at higher RPM.*

Heat build up would depend on the firing cycle, and the input voltage and amperage.
I see no coil failures to speak of anymore. It's really not an issue.
Theoretically, heat would cause more resistance, and reduce output...
*b. Heat Build-up in the ignition module at higher RPM.*

This factor is still a concern. Factory modules are more susceptible to heat failure than the aftermarket ones seem to be at high RPM, but on street driven vehicles, I don't see any difference.
*c. Hall effect switch times decrease with RPM.*

The trigger time is unimportant, as long as it is sufficient to trigger the module.
(The module takes care of all of the issues like dwell, and duration, it only needs to know WHEN to fire)
I have see stock Ford and Mopar Hall effect triggers live at 16,000 RPM on the test bench every day.
I don't think even the most rabid Jeep engine builder is going to REV above 16,000 RPM!
On the other hand, I have yet to see a GM style trigger stable above 6,500 RPM.
Even the expensive aftermarket GM style triggers won't stay stable above 6,500 RPM.
Slap that big ass magnetic field over it from the ignition coil, and it gets REAL unstable...
If you know of a GM trigger that will sustain signal above 6,500 I sure wish you would let me know who makes it. I have several hot to trot GM HEI guys that would love them.
*d. Higher compression requires a "Hotter" spark*

I have worked on USAC and CART champ cars (Indy type cars), and I have also worked for two major manufacturers of force fed engines. My first hot rod in high school was a twin turbo small block camaro. I didn't even have a license yet when I started on it.
I can tell you from experience, 30,000 to 40,000 volts is more than enough to fire the hole at even three atmospheres.
There are several companies that make capacitive discharge ignitions that will do the deed correctly, but not one factory inductive discharge unit will.
Spark duration is the important thing after about 7,500 volts.
No factory inductance discharge ignition will go past 120 micro seconds, no matter who makes it. There isn't anything you can add on to change this fact. The only way is to go CDI.
(Take a real long hard look at the turbo GN and GNX ignitions, and get back to me.)
*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.*

Why didn't you address spark quality? You know, when those misguided guys use those MEGA coils that blast out 75,000 volts (or what ever) I've seen them advertise 100,000 volts out of a inductive discharge coil.
Ever seen that thin, white, thready spark that doesn't last but 60 or 65 micro seconds?
Pretty nasty, and not long enough or rich enough to really do the job.
Coil saturation is determined by the manufacturing process. Factory coils seem to have the best coil outputs, all things being equal in bench tests.
Voltage to the coil, and delivered amperage are both controlled by the installer, by wire size mostly. (Not counting the guys that left the resistor in the system) You, me, MSD, Jacobs or the man in the moon will never have any control over this part of any upgrade.
All we can do is keep repeating what it should have and hope they were listening at that moment...
*II. Jacobs Ignition Systems.*

I don't like degrading and body that is trying to make a living. I especially don't like making statements against a specific product.
I have had Jacobs ignitions on the bench, and in real world testing.
I don't use them.
I have two here now if you would like them.
*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*

Says who, you or Jacobs? (Or their advertisements?)
Their basic designs are about 30 years old, just like all of the CDI ignition designs are.
I have never seen Jacobs in the winners circle anywhere.
I don't know of a single national title Jacobs has ever won.
I don't personally know a single person that has used Jacobs products that liked them.
I have seen about 100 to 1 comments against Jacobs in written opinion.
Just read this BBS for verification.
I have never had a good experience with Jacobs tech line, or their customer service.
*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.*

Nice quote from the sales literature.
What you just said is, 'We have tinkered with a 30 year old CDI ignition, and now we have added so much stuff it's not reliable, dependable, or affordable, and there is no way that the normal guy can work on it, or get parts for it.'

Also I noticed you didn't address the timing drift problem, or the dwell instability problem they have...
Just for your information, if it was real plasma, it would melt the engine block into a puddle. It takes huge lasers, and fissionable material at about the temperature of the sun to create real plasma.
Check out any collage energy physics web site for more details.
Plasma is an over used word, just like plasma cutters, plasma lights, plasma discharge, ect.
It's not as bad as the Y2K thing was yet, but give it time...
*It's dynamic, constantly changing.*

That's what dynamic means. It's not always changing for the better though, if my bench tests are correct.... (and they usually are...)
*Diagnostics are harder to do…. And parts and help is through Jacobs or their re-sellers.*

Help available through their re-sellers.... SOME JOKE!
A speed shop guy is supposed to SELL YOU STUFF. They don't service it, and most chances are they can't give you anything but generic "maybe fixes' and they aren't getting paid to work on your car, so they are NEVER going to take the time to find the problem,
EVEN IF THEY WERE QUALIFIED to do the work. And I'll guarantee 99.9999% of them can't find the gas cap without help. How is a sales man going to help?

To get it serviced, you have to send it back to Jacobs. Jacobs is going to give you a ton of grief, charge you at least $35.00 to even unpack the box, and tell you it's fried, and you have to buy a new one... It's the same story I just keep hearing. AND I heard it first hand two years ago.
*Some systems are 50 State Legal, some systems are off-road only….*

OK, I'll buy that one.
*Installation is harder, but your OEM ignition system can still be plugged back in if there is a failure.*

You bet it's harder. I guess if you buy the adaptors from MSD you can still use your stock system again. If you follow Jacobs instructions, you have had to cut all of your factory plugs off....
*MSD systems use less sophisticated electronics than Jacobs*

What MSD unit might you be talking about? If it's the MSD 6 series, then you are correct. MSD 6 series modules are a basic design that is about 25 years old.
The internals of the unit have been updated with modern components several times, but the basic function is the same as originally designed.

You better take three giant jumps backwards if you are talking about the MSD 7, 8, 10, and digital series. They just kick Jacobs back to the stone age.

BTW, MSD modules and ignitions were on all automotive products national winners again this year. THAT'S ALL WINNERS.
Have you ever seen a Jacobs in a NASCAR? How about a NHRA Top Fuel or Funny Car? How about any off shore power boat racer?
NO? there is a reason for that...
*to fire multiple sparks of a set, specified power level, through out the dwell cycle.*

That's what it does, but that's not the idea.
The idea is the increase the duration of the discharge time. The longer the 'spark' lasts, the better chance of getting the fire lit in the cylinder.
MSD fires for about 20 crank degrees, and that is about all it can with out risking cross firing in the cap.
It's still about 1,000 to 1,400 micro seconds, more than ten times the duration of a stock system, and more than twice as long as Jacobs.
*This produces a cleaner burn of the plasma, but not as optimized as Jacobs. It is a static system.*

Again, what MSD system are you talking about?
MSD does start the flame front more stable and more reliably than Jacobs. It is not a static system. It shortens the cycle as the RPM increases, and it adjusts voltage to the coil as to RPM.
*Because parts are simpler, and the design is stable, diagnostics is easier, parts are less expensive.*

Because MSD is the original, and not a jonny-come-lately-knock-off, done poorly, it is more reliable. MSD spends great amounts of time and money in research and development, testing and racing.
Of course it's stable, you can't win every single NASCAR race if you don't finish...
Same with NHRA, IHRA, CART, IRL, and every other car racing forum...
It's no accident that guys with a million dollars riding on every race use MSD...
They don't use it because it's cheaper than Jacobs or any of the others...

The Ball Peen Hammer is a very old design, but I still haven't seen a replacement for it either...
*Help is through MSD and it's resellers.*

Not true, a flat out false hood.
MSD Tech line is free, and it goes directly to MSD Tech offices in El Paso.
MSD dealers are required to take training to get the W/D program.
MSD has protected sales areas, so there is great competition keep them. Customer service complaints is the best way to loose a MSD dealership I know.

Vic, Roberto, Joe, Geno, and Dirty Dan are all race track veterans, and know the ropes.
All have worked in the rebuild and warranty rooms.

I have never been charged a nickel to have any MSD product tested or fixed.
I know they do charge for stupidity kills, but they have never charged me a thing.
I have told them I bought modules second hand, and needed them serviced, and it's still not cost me anything but UPS charges to get it to them.
They usually include the wiring ends, rubber feet, and hardware package when they ship it back also.
*Some systems 50 State Legal, some systems off-road only*

All of the MSD 6 series and digital units are 50 state legal, and CARB approved.
I have only recommended the 6 series modules.
They beat Jacobs in every way,
Cost effective, Emissions legal, CDI Performance upgrade, Works with every factory distributor and coil, upgradable even to heavy racing, Reliable as an anvil...Ect, ect....
*Installation is much simpler than the Jacobs, and your OEM system can be restored quickly.*

Installation is simpler than installing a factory system.
MSD can be ran with the factory ignition still hooked up. MSD offers a single throw switch that can put the factory ignition back on line in one second. (P/N 8808)
*The coil is located in the rotor cap. This reduces power loss delivered to the plug.*

The coil throws a huge magnetic field around everything in the cap, including the pickup coil, module and wiring. That magnetic field causes false firings in the pickup (random firings), and inductance firing in the wiring (more random firings). It also inhibits the proper functioning of the module when it's supposed to fire.
Ever wonder why GM didn't shield that wiring from inductance?
The coil housing is impossible to seal for moisture because of the wiring hookup design.
The coil is impossible to keep from leaking high voltage into everything.
The coil is impossible to keep it from firing out side of the cap or inside of the cap.
The small amount of power loss in the coil wire isn't going to make a bit of difference at the plug when the coil is firing at random...
*The coil is powered at the full 12 supply voltage, rather than the switched 8 voltage of the stock FOMOCO.

The voltage to the coil has been addressed by me more than once. I don't know why you are still hanging on this point.
Where did you find a reduced voltage coil with a Dura Spark module?
If you go to a MSD 6A or 6AL you won't need to worry about coil voltage anymore, or the HEI. Just use the Motorcraft distributor to fire the MSD, and use the stock coil in your new CDI ignition!!
*This helps to produce the "hotter" spark.*

The only thing that will help an inductive discharge ignition is a ignition coil with a higher winding ratio.
Them is the facts!
The coil is nothing but a stepper transformer. The only way to increase the step up inductance effect is to increase the number of secondary winding compared to the primary windings. Just simple, basic electrical phenomena, and basic physics.
Jacobs ain't the only one with some school learnin'!! I graduated the 6th grade too!
*Also, the GM HEI module is a fast switching module, so that it will help the coil to fully saturate at higher RPM's.*

That is true, but the trigger wouldn't function reliability above 6,500 RPM, and the stock module starts to become unreliable at 3,500 to 4,500 RPM so what's your point?
If you can't achieve high RPM under load because of module and pickup failures, why would you care about saturating the coil at RPM you can't reach?

Never tried to race one of the GM HEI's at above 4,000 RPM have you?
It takes a Ford or Chrysler pickup (like MSD uses) and a Borg Warner module just to get them to 6,000 or 6,500 under load. Then they are arcing all over the place, and destroying a cap and rotor every time out...
*These are the two reasons that the stock GM HEI is an improvement over the stock FOMOCO system.*

You are allowed to think anything you want, this is America.
I'm just going to have something to say about it when you try to pass off your opinion as fact instead of saying it's just opinion.
*The faster the module and coil react (pardon the electronics pun) the faster, and the "hotter" the spark produced.

You are pardoned.
You are also wrong.
With all things being equal, the only thing that can produce a 'Hotter' spark in an inductive type ignition is a higher winding ratio count. 12 volts going in at 10 amps is 12 volts going in at 10 amps. The module is just an on/ off switch. On and off is On and off. the new DuraSpark have just as fast of switching as the GM HEI modules. In fact, take on apart, and you will see they have the same drivers.
*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.*

An as was covered before, 30,000 to 40,000 is sufficient to light even the most stubborn top fuel engine. It's spark duration that is the biggie after you achieve 20,000 volts.
Or don't you believe Smokey Yunick, and guys like him?
It's obvious you don't believe me...
*The next issue is hystersis and eddy current build up and heat dissapation in the coil.*

You didn't mention coil rebound and potential double firings...
This is just academic speculation. Coils have been pretty well engineered for you or I to start trying to find shortcomings in them...
Heat dissipation isn't a problem anymore. When was the last time you saw a rash of burnt out coils in the summer time?
I do know if you try to run the GM HEI remote coil, like for the early 80's 4 cylinders, on a V-8 system, it won't live long.
I tried a Ford distributor and DuraSpark with a GM HEI remote coil looking for the best of both worlds, and the coil fried pretty quick....
Can you honestly say you have done any testing like that?
Can you honestly say you have tried EVERY combination of parts you could think of? And tested everything heads up on a bench to cut through the bull sh*t and hype?
Have you given everything it's fair share of abuse to see what lives and what doesn't?
Have you ever built you own crank triggers just to make sure the cam wasn't adding any timing variation to the mix?
To quote a mentor I once had, "Leave no stone unturned, and then roll the son of a bit*hes down the river bed until they are round, then, and only then, will you have the truth of the matter."
Words to live by!
*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.*

Yes it would. But like I said, I don't see many dead coils these days...
*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 do Motorcraft distributors. Motorcraft just puts the centrifugal advance under the distributor floor plate to keep it away from harm, like the GM HEI coil welding the snot out of it, or some Dilbert trying to change things when he hasn't got a clue what he's doing. Springs for most Motorcraft distributors from Mr. Gasket, P/N 925D.
Most people don't know that some of the GM and Ford springs are interchangeable.

The only pain with the Motorcraft distributor is you have to pull the distributor,
Drop the drive gear, and remove the vacuum advance, and take the screws out of the floor plate and lift the entire assembly to change springs.
It's a pain, but well worth the effort.
*So, if you have the desire, or need to play… you can.*

Just what the world needs, some more six thumbed busters trying to out smart the factory engineers.... Oh well, it keeps the local shops in business....
*Also, faster ignition modules and coils are available through many after-market sources if you want to "soup up" this system*

I thought you and I were talking about stock system upgrades?
If I go aftermarket, I'm not going to spend a bunch of money on a GM HEI, the upgrade it trying to make it work correctly,-- I'm going to install a MSD 6A module on my factory Motorcraft distributor and coil, and stomp a hole in any GM HEI upgrade.
*… just do your homework.*

Best advice anyone could ever give to anyone!!!
*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.*

I hate to sound like a broken record, but the Motorcraft/ MSD 6A Is 50 state legal.
Is it easy to do? Yes. It is costly? Depends on where you get your parts!

Heard that twice. I'm a real parts scrounger. I will buy and rebuild a core from a scrap yard, even if it cost more than a so called, 'remanufactured' unit. I just like to know everything is correctly done, and I usually learn something...
*Is it dependable? I'd never heard a discouraging word about the GM HEI swap until Aaron offered his information.*

Now this is the part where we may have a problem....
I just reported facts.
Have you never seen red dust in a GM HEI? Have you never seen the carbon buildup on the rotor, or the carbon tracks? Have you never seen the end of a rotor burnt to hell and back because the thing had a 1/4" air gap instead of the recommended 0.015"?
Have you never seen GM HEI weight pins eaten half through and the weights slotted from the spark welding them to the posts?
Did you think friction did that to the posts and weights?
If so, why are the posts eat out in the inside, shouldn't it be the side that the weight pulls on, the top outside if it were friction?

Do you think I make this stuff up?
*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.*

I agree with that. And I have said that as an upgrade for points, the GM HEI should be considered.
It's perfectly capable of doing the same adequate job of firing the cylinders as the Ford DuraSpark is.
I said there is no reason to strip off you emissions approved Motorcraft/ DuraSpark ignition system when a $60 Cap/ Rotor/ Plug wire/ Springs upgrade with make it just as trustworthy and potent as the GM HEI.

And when it comes time to add that MSD 6A module, you are ready to kick some GM butt then!
*Can the OEM FOMOCO system be operated as a twin system?*

I'm not sure what you mean by 'Twin System'.
Two Motorcraft/ Duraspark systems can be run as backups to one another with just the flip of a switch.
So can MSD/ DuraSpark systems.
I have done both ways. There is even room for a second pickup module in the distributor to complete the separation and make two complete systems.
I really see no need for something like that except for emergency vehicles...

I see no way to do a GM HEI and a motorcraft dual 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.

I think you lost me on TAC...
You can use ANY OEM module to fire ANY OEM system. I've spliced and grafted every mix I could think of. Some of them are just damned silly....
*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.*

Thats not having much faith in your chosen conversion..... (...Sly grin...)
I believe in the sh*t happens school of though also, but I don't see taking repair parts for two different ignition systems along....
*So far, excluding wiring questions, the GM HEI delivers improved performance*

Improved performance over what? If you are talking about points, I agree.
It doesn't out preform the Motorcraft/ Dura Spark. in stock configuration, and if you add an upgrade, it should be the MSD 6A module, then the Motorcraft/ MSD configuration stomps a stock GM HEI to a bloody stub!
*for a low price, off the shelf, easy to retro-fit ignition system.*

The key work is retrofit. Hell, you know the drill by now, I'm beginning to sound like a broken record..
(anyone remember vinyl records out there....)
*This system has been used for several years on Toyota's, Ford's as well as retro fitted to several European autos and older GM engines.*

I don't know about Toyota, I've never seen a factory GM style HEI on a toyota, but I don't do imports unless I'm dating the owner of said vehicle.
I pay no attention to eruo-trash. Those thieving bastards have never had an original thought.

Point out one Ford anything that came out with a GM style HEI on it.....
I'll lay money on this one....
*It's reliable enough that other companies, including MSD, make improved versions of this system and sell them at a substantial profit.*

Hell yes MSD makes stuff for them! There is only about 140 million HEI vehicles out there in north America alone! You would be stupid to ignore a market share like that.

BTW, MSD GM HEI modules are the heart of one of your beloved after market HEI makers systems. They use MSD modules, coils, and timing accessories like rev limiters, and boost control systems. Just stick their stickers right over the MSD stickers and send them out.
It's called private labeling, and it's legal.
*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.*

Stated as opinion, and I can't comment on opinion. Thats a matter of personal taste.

BTW, if you intend to go MSD, have a look at the trigger in nearly every aftermarket distributor. Almost everyone uses a Ford style trigger, and that is for Chevy, Ford and Mopar replacement distributors...
Ever take a good look in a Jacobs distributor?? Tell me what you see......
*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*

You also said you never gave the Motorcraft a chance. Did you do the cap/ rotor/ plug wire/ springs upgrade? Tell the truth.....
You just pulled it and slapped in a GM HEI. That is your choice and it's OK by me.

I'm just trying to give people who ask all of the facts, not make their choices for them.
I give them the facts, and they choose. No matter what anyone chooses, I'm not going to loose a minute's sleep over it.
I will loose sleep if people I have come to know pay $450 to $600 for some MSD knock off or GM HEI because no one told them the truth...
* 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.*

Too bad, I could have used it if you were just going to give it away...

I'm glad you are happy. It's your choice. You weighed the facts as you knew them, and made your choice.
Please don't try to distort the facts so others can make their choices....
The old points type Delco distributors can be upgraded to electronic ignition trigger also.
Several companies make the kit, and normally it's is under $100 dollars.
That trigger will allow anyone to use any module he or she wants to control the coil.
If you are good with a die grinder and J B Weld, you can update you distributor yourself.
Get the trigger and reluctor form a 1976 New Yorker with a V-8.
The reluctor can be ground out to fit over the cam lobes that actuate the points, and the pickup coil assembly can be taken off of the Chrysler advance plate, and mounted on the Delco advance plate. Cost, around $15.00

MSD 6 Series modules are set up to fire from points right from the factory. The voltage to the points is so low that a set of points will last virtually forever, and dwell problems be damned!

If you made it through all of this, you are truly hard core.....
Happy trails folks... Aaron.

If a tree falls in the forrest, and there is no woman around to hear it, is the man still wrong?

13,432 Posts
Re: Answer for LEVE\'s ignition questions...(LONG)

Wow... I feel like I've had a trip to the woodshed...

I am interested in all the information I can get on this subject:

1. Can you give more information on the GM HEI coil splaying RFI into the ignition module wiring and causing false triggers. Does MSD shield the module and associated wiring?

2. You stress high RPM results. I drive like I fly, low and slow, my engine rarely goes over 3500 rpm. IYO is the stock HEI system going to meet my needs?

3. CJDave speaks to possible mechanical failure of the distributor shaft when subjected to off-road stress. Have you seen this failure?

4. You suggested I never gave the FOMOCO ignition a chance...Why? The original distributor was in poor shape when I purchased the CJ with 128,000 miles. I replaced it with a bone stock rebuild from NAPA for $60, as well as the plug wires, rotor, cap and plugs. Then I ran the engine for another 15,000 miles. The 258 engine did smooth out. but not throughout the RPM range. However, with the GM HEI, all hesitation is gone throughout the normal RPM range.

5 Will the GM HEI distributor mechanically stand up to another 120,000 miles of usage?

I hope it will, and if not I will have learned a lesson.

Good Jeepin'


6,394 Posts
Re: Answer for LEVE\'s ignition questions...(LONG)

/wwwthreads_images/icons/tongue.gif Actually, I was concerned only with the V8 retrofit... Where the GM is grafted onto the top of the thin Motocraft stalk./wwwthreads_images/icons/wink.gif Wow...I used up all my "extra" time on that thread....I'm late for my generator test! I was supposed to leave no later than 3:30! Bye!/wwwthreads_images/icons/crazy.gif

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

6,870 Posts
Discussion Starter · #4 ·
Re: Answer for LEVE\'s ignition questions...(LONG)

*Wow... I feel like I've had a trip to the woodshed...*

That wasn't my intent. Sorry if I came across that way.
You have an understanding of the basics, and you seem educated on the subjects you speak of. I would never lay into anyone that was actually trying to learn.

Besides, the woodshed here isn't a bad thing, that's where we keep the beer and summer sausage fridge!

I wouldn't be afraid to let you work on my stuff, and I'd hire you in a second!
You ARE NOT the usual tobacco juice drooling, nose miner that starts trouble, and spouts off about his 3/4 race cam... and "F**KING JUNK HOLLEYS"... You know the type, we've seen them here...

You do a good job of stating facts as you know them, and clearly prefacing opinion as just that-- Opinion.
You don't seem to mix the two, and that is good. You have to know what you know, and you really don't know anything until you see it with your own two eyes....

I just believe you have relied too much on the written information, and not done enough testing.... (but I have a sneaking suspicion you will now....)
Sorry again if I was too 'gruff' as CJ Dave says...
*I am interested in all the information I can get on this subject:*
*1. Can you give more information on the GM HEI coil splaying RFI into the ignition module wiring and causing false triggers.*

Not true RF noise, it's simple magnetic inductance. There has to be a price paid for that HEI coil... right over everything....
*Does MSD shield the module and associated wiring?*

As a matter of fact, MSD does make a EMI (Electro Magnetic Interference) shielded cable, P/N 8862. It should drop the engine block right out of the distributor housing, and ground. We drill a hole right under the pick up coil wiring and drop the Hall trigger wiring straight down to get away from the coil.
The stock unit winds around, and plugs into the Module, all inside of a huge magnetic field that collapses every time the coil fires. Some times it fires it's self. See what I'm getting at?

MSD replacement modules DO address the transient firing errors with anti false trigger circuitry and grounding. The modules are able to decide if it's the correct time to fire by seeing what the RPM was a few milliseconds ago, and deciding if it truly time to fire again yet...
*2. You stress high RPM results. I drive like I fly, low and slow, my engine rarely goes over 3500 rpm. IYO is the stock HEI system going to meet my needs?*

I also stressed that if you stay at low or normal engine speeds, either maker will work...
Both ignition systems are 'Common Voltage, Inductive Discharge'. There really isn't a whole lot of difference one way or the other. Both will fit the bill. Ford just has less spark loss problems and less spark energy going astray. It's the cap and rotor design.

A lot of guys are going to install a HEI just because they like to tinker, and the can...

Some are after a little more pick up, and changing to the HEI's faster ignition curve will do just that for them. Most never seen the springs in a Motorcraft distributor, therefore didn't know about them. They usually didn't know about what made the HEI more 'zippy', just that most people thought it did.

Get rid of the resistor on resistor equipped models, and change to the large cap and rotor, good plug wires, and change the springs, and the Motorcraft will do the same thing.
It's all a matter of what information people have. If you don't have the information, you can't use it...
*3. CJDave speaks to possible mechanical failure of the distributor shaft when subjected to off-road stress. Have you seen this failure?*

YES! It is rare, but I know of mild drag cars (Shift at 6,000 RPM) leaving the line hard enough to snap the housing off. There is usually a obvious flaw like a bubble or casting stop and start line that was the root cause, but I have seen it in the factory HEI housings.

He was talking about the bastard weld mating of a Ford stem to a HEI head anyway.

If I was doing it, and I have just to see if it works, is turn the housing down on a lathe and cut the shaft on a GM HEI to make it fit the AMC V-8.
In the AMC V-8 the distributor sets at about a 40 degree angle to perpendicular. The weight of the head alone in over twice the weight of a Motorcraft head. It's just got to be stressing the stem...

Believe me when I say that the early Motorcraft distributor housings are no prize either...
The casting guys must have been on a seven year drunk when it comes to the AMC Motorcraft housings....

I also worry about the centrifugal advance weights. GM HEI uses huge weights compared to Ford, and that angle has to be affecting the weights... I just haven't leaned the distributor machine over to see how much it affects them yet...
(My back is injured, and if you never lifted one of those old Sun distributor machines, you don't know what your missing!! It takes two men and a boy... At least a six beer job!)
*4. You suggested I never gave the FOMOCO ignition a chance...Why?*

You never said anything about doing the Ford cap, rotor, plug wire, advance spring upgrade before switching to an HEI.
Comparing a GM HEI and a Jeep/ Motorcraft ignitions isn't a level playing field.
Jeep went dumpster diving for distributor caps, rotors, plug wires ect, and if you want to put a 50's cap and rotor on the HEI to compare, it's OK with me.
If the jeep is brought up to the same specs as it's same year model Ford counterpart, it can compete with GM HEI in every way except advance curve.
Now we are down to a $4.00 spring kit upgrade to make them dead even...
See my point?
I'm trying to save these guys a bucket load of money... and dispell the old wives tale that the Motorcraft/ DuraSpark ignition is just junk and can't be helped....
*The original distributor was in poor shape when I purchased the CJ with 128,000 miles.*

That's the beauty of having no physical contact with the trigger like points do. The distributor bushings can be shot to hell and back and still trigger the Hall effect coil, and have no effect on dwell. Dwell is take care of in the module...
*I replaced it with a bone stock rebuild from NAPA for $60, as well as the plug wires, rotor, cap and plugs.*

Did you go to the Ford style 2 piece cap, rotor, and HEI plug wires? Or did you just get that 1920's designed stuff that Jeep puts on there stock.
Did you bring it into the 70's or leave it in the 20's?
*Then I ran the engine for another 15,000 miles. The 258 engine did smooth out. but not throughout the RPM range.*

Did you look for any other causes, like a bad vacuum advance, old weak springs that some south American reused when he rebuilt the distributor, old weak ignition coil, corroded wiring connections, distributor pickup wiring too close to the spark plug wires, Ect, ect...
Or did you just blame it on the stock ignition?...
*However, with the GM HEI, all hesitation is gone throughout the normal RPM range.*

Hesitation can only be caused by one thing in an ignition system. Advance curve. Initial advance, vacuum advance, centrifugal advance and stray timing transient errors in every module make up the advance curve.

BTW, you didn't happen to put a new carb on about the same time you did the GM HEI swap? Hesitation is usually bad fuel delivery curve.... but that's another article...
*5 Will the GM HEI distributor mechanically stand up to another 120,000 miles of usage?*

I know guys that have over a million miles on them, I don't see why not.... Just remember to lube the top bearing grease well so the top bushing stays lubed.
*I hope it will, and if not I will have learned a lesson.*

I hope so too. I learn something every day...
I really like the Motorcraft distributor for anyone thinking of moving up to MSD. It makes life SO much simpler! The cap upgrades make it my distributor of choice for a Ford or Jeep, MSD upgrade...

Here are some ideas for you....
How about a Motorcraft/ Dura Spark with a Ford TFI (Thick Film Integrated) coil?
How about a Motorcraft/ Dura Spark with a GM 'Dual Connector' coil?
How about a Motorcraft/ MSD 6AL with GM 'Dual Connector' coil?
(you should be able to weld with that output!)

The Motorcraft/ DuraSpark and Motorcraft/ MSD combos killed the GM HEI external coil for the 4 cylinders, but that's what made me just think of the 'Dual Connector' coils....
Those 'Dual Connector' coils were even used on some of the factory supercharged engines... Now I'm on to something.....

Talking to you has made me think... and that is a good thing right now...

Later all... Aaron.

PS, I just re read this post. If I get any more long winded, I'm running for congress...

If a tree falls in the forrest, and there is no woman around to hear it, is the man still wrong?

Re: Answer for LEVE\'s ignition questions...(LONG)

Thank you Team Rush the reply you gave was top notch. The main reason i use this board is all the great knowledge that seams to reside here and hearing multipual answers to questions alwas helps to make informed decisions. There is a welth of experence here and it helps those of us that are learning without spending a ton of cash to learn the hard way.
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