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GM HEI vs. Motorcraft/Duraspark ignitions (very long)

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  • GM HEI vs. Motorcraft/Duraspark ignitions (very long)

    Everything below came from searching the Off-Road.Com forum for posts about this topic by a member called TeamRush.

    * * * * * * * * * *
    The GM style HEI was developed for, and made it's racing applications debut in 1966.
    The basic design wasn't changed until it was discontinued in the 1990's

    The GM HEI was the first generation of electronic distributors, and like any first generation, it had flaws.
    (Lots of flaws!!)

    Ford pretty much waited until GM did all of the full scale research and development, took all of the good points of the GM HEI, and designed out the bad parts of the GM HEI to come up with the Motorcraft/ DuraSpark Ignition in 1976.
    (So did Chrysler!)

    A lot of you are too young to remember, but points had to be adjusted about every 3,000 miles max, and replaced every 10,000 miles, or you got to walk.
    (and it always seemed like it was at night in the rain when they quit!)

    Along came the GM HEI, and that changed over night!
    It was leaps and bounds over the basic points system that had been used since the 1920's.
    But the original GM HEI was still triggered by breaker points.... And was REAL hard on points with the new E-core coil design.

    In 1974, the first of the all electronic 'Breakerless' ignitions came out, meaning they had a 'Hall Effect' Trigger, rather than a set of breaker points.
    They also featured a transistorized switching module that GM HEI used to the final death twitch of the HEI distributor.

    The biggest draw back to the GM HEI is the coil in the cap, and the module in the cap design.
    Coil in the cap means that all of the Radio Frequency Interference, and Electro-Magnetic Interference that the coil produces (and believe me, they are REALLY cranking out the 'noise'!!) is directed at the module and the pick up trigger coil...
    (Ford fixed this by moving the module and coil to different locations.)

    And if that weren't enough, the high voltage from the secondary side of the ignition passes within 1 1/2 inch of the module!!
    One ground fire to the module, and you walk!
    When the high voltage escapes to ground inside the distributor,
    (That's when, not if...) you are guaranteed a false firing of the Hall Effect trigger.
    (Ford fixed this by using a much taller rotor, and shielding the Hall Effect trigger.)

    The center electrode (Button) is normally a soft, relatively high resistance graphite.
    This graphite comes off when the voltage is passed through it, and when the electrode comes into contact with the moving rotor, and small amounts of CONDUCTIVE graphite are distributed all over the inside of the cap and on the rotor, causing the high voltage to follow it, instead of going to the spark plug terminal like it's supposed to.
    If you see black dust in the cap, or on your rotor, you have the problem.
    (Ford uses a much harder, and lower resistance center electrode to correct this problem.)

    With the short rotor barely covering the internal centrifugal advance mechanism, you are guaranteed to get lots of firings to ground, both around, and through the rotor.
    (Look for 'Red Dust' inside your cap and rotor. That is the residue of extreme heat 'welding' the advance weights to the pivot pins from ground firing.)
    (Ford Solved this problem by using a much taller rotor, physically putting distance between the distributor internals and the high voltage.)

    The HEI distributor cap is non-vented, so the high energy discharges build up ionized air, called Ozone. This ozone promotes ground fires, cross fires and chain fires inside the cap, further adding to the confusion...
    (Ford fixed this by venting the distributor housings, and in some cases, the caps themselves. Also, Ford uses vanes in the cap to stir up the air and keep the ozone from collecting in the top of the cap.)

    There is a lot more, but it all gets VERY technical from here, and we will start to loose people at this point....

    Lets get to electrical...
    The GM HEI coil was a real voltage monster in it's day, but it's very tame by today's standards...
    Voltage is just the beginning of good spark energy anyway...
    The three components required for proper spark energy are...
    Voltage, Amperage, and Duration of spark (Discharge Duration).
    GM HEI coils can produce adequate voltage, but lack any ability to increase duration or amperage to acceptable levels.
    Stock GM HEI's can't even produce acceptable voltage levels because of bad wiring feeding them, or the factory modules don't have the ability to switch enough power to them.
    (Ford uses the third generation E-core coil to produce Voltage, Amperage, and Duration, but it's still just an inductive ignition, so it's marginal at best.)

    The GM HEI module switches the power on and off to the coil.
    The switching transistors used in stock type modules are not capable of delivering enough current to the ignition coil to make it work correctly, and imported 'economy' modules are even worse.
    Putting a 'Super Coil' in the cap makes matters worse, because they require even more current to work correctly.
    (Ford is no power house when it comes to power switching, but it's slightly better than the GM HEI. Both ignitions are weak in this particular field...)

    The GM HEI module has the ability to change dwell with engine RPM.
    (This is a feature no DuraSpark module was ever designed with, and is a great idea in theory...)
    The problem is the dwell 'drifts' around so much, usually as much as 50% of it's total, that it's unpredictable, and detrimental to repeatable performance.
    (GM has Ford here. This is not offered on DuraSpark modules. DuraSpark has a fixed dwell.)

    The Hall Effect trigger used in GM HEI distributors is the same basic design that was first used in 1966, and produces the weakest signal of any of the major three factory ignitions.
    It's large, exposed windings are particularly susceptible to EM and RFI noise causing false triggers, and it's weak signal is often not capable of firing the module creating a miss in the firing order, especially if the connectors on the module or Hall Trigger are the least bit corroded or dirty.
    (The Ford style Trigger is the strongest signal maker of the big three. Wiring on the Ford connectors is entirely up to you, they are external, and if you clean them, and properly seal them, there is never a problem.)

    The GM HEI's good points are...
    --With the one piece cap with no vent, the cap works as an air bubble to keep the high voltage circuit moisture free when driving through water.
    --The GM HEI is a one piece changeover, meaning if you have to change distributors, it's loosen one bolt, pull a couple or three wires, and change the distributor.
    --There are parts for them at every discount auto parts store, and most farm implement stores in the country (and abroad for that matter)...
    --They are EVERYWHERE in junk yards for cheap...
    --A fresh Reman with core charge at the discount parts store is under $125.

    GM HEI CHANGE OVER... Do's and When To's....
    1. If you have a Prestolite distributor and ignition system, a GM HEI is a good thing. (So is a Motorcraft/ DuraSpark ignition)
    2. If you have NO money, and Access to an I-6 GM HEI distributor and AMC V-8 Drive gear, and need a different distributor, GM HEI is a fair swap.
    3. If you have a Breaker Points Distributor, and you need a replacement, and you have a GM HEI and no money...

    If you already have a Motorcraft/ DuraSpark ignition, (1978 to 1990 in the US) the 'TeamRush' upgrade is the way to go.
    Cheap, Easy, No special tools or parts required. Just tune up parts and away you go. NO DISTRIBUTOR CHANGE REQUIRED!!

    If you have the Prestolite ignition, you are screwed.
    GM HEI or switching over to Motorcraft/ DuraSpark are both viable alternatives, since the distributor, module and ignition coil all have to be replaced.
    The GM HEI is a little less wiring, but personally, I prefer using the Motorcraft/ DuraSpark system simply because it was designed for that engine and vehicle type.

    If you have breaker points, and you want to upgrade, you have more than just the Ford or GM choices....

    If you have breaker points, you already have a Delco distributor.
    There are a few kits on the market to adapt your distributor to electronic triggers, then you can use a variety of modules and coils.

    You can use the $10 Chrysler trigger and reluctor to upgrade your distributor if you are low on cash, but handy with a round file or Dremel tool.

    You can switch over to the Motorcraft/ Duraspark ignition with no trouble at all. It's all drop in parts, and there is a little wiring to do, but it's very simple and diagrams & instructions are very available.

    You can do the GM HEI change over with just a little more fuss finding the correct parts to modify the distributor, and of course, you still have to modify the wiring to accommodate the GM HEI distributor....


    Here are a few things you can do...
    1. Use a distributor cap and coil from a 1976 Chevy pickup with an I-6 engine.
    The HEI distributor in '75 & '76 used a remote coil (not in the cap).
    You can also switch in the more potent Ford TFI style coil in this situation, just make sure you get the coil polarity correct.
    The '76 cap is vented, the '75 is non vented, both use the later style HEI plug wires.

    2. Use a premium quality distributor cap with brass terminals. This will deliver more of your hard earned spark energy to the spark plug, instead of absorbing or scattering it like aluminum or tin connectors will.

    3. Use a PREMIUM TYPE ROTOR that completely covers the advance head and weights, and preferable has ridges or slots to stir up the air and to trap

    4. Use a good quality set of Hellically wound spark plug wires, with good 'Snap' connectors and good silicone, high temp boots.
    NEVER PULL ON THE PLUG WIRES, twist the boots, and pull on the boots only!

    Resisted (Carbon Core, Polyester/ Graphite, Hellically Wound, Ect, are alright, with varying degrees of success........ but NEVER SOLID COPPER OR STEEL CORES) wires are a must to keep the coil/ module alive
    They make way too much EM and RF noise, and will cross fire between them selves with the voltages generated by an E-core style coil.

    6. Open up the plug gaps, (around 0.040" to 0.045" in most cases) and use a good quality copper core plug.
    Autolite, NGK, Nippon-Denso seem to make the most reliable plugs.
    (I can find no reason to use Bosch Platinum, Any multiple electrode plug, or anything like Splitfire plugs in anything.)

    7. Get some dielectric grease, and learn how to use it!
    A little dab on the rotor nose will make a lot of radio noise go away...
    A little dab in the spark plug boots and distributor cap boots will make your connections easy to get off during service, and keep moisture out.
    A little bead on the distributor cap lip makes the distributor cap connection point virtually water proof.

    9. IF YOU HAVE A GM HEI....
    Use a Continuous Hold Solenoid and 10 AWG wire to supply the distributor's current demands!
    A 15 amp relay will do the job too, and may not take as much current to trigger it, but a relay of some kind and 10 AWG or larger wiring is REQUIRED for optimum operation of the GM HEI ignition...

    (Notice ALL GM vehicles use at least a 10 Ga. wire, and some of the factory High Performance models use an 8 Ga. wire to supply the HEI?..... I did....)

    10. If you want to remove the coil from the cap, but can't find a '76 I-6 distributor to use, the parts from a I-4 GM HEI will work except for the Hall Trigger, which does not change from one I-6 to another in the early years...
    The I-4 distributors grow on trees, have the correct coil wires for the GM remote coil, use the same modules as the I-6 in most cases, and all the parts will interchange...
    (Gotta' love chevy for interchangeability!!)

    * * * * * * * * * *
    Whats the diff between the HEI upgrade and the TR/TFI upgrade?

    Fair Question...

    The "TeamRush" ignition upgrade uses the stock distributor,
    (Which is an excellent design, and functions very well, ask any Ford racing guy.)
    It uses the stock ignition module, and all of the stock wiring harness.
    All you change is the distributor cap, rotor, plug wires, and if you can afford it, the ignition coil.

    The stock type distributor will keep the vacuum advance where it's supposed to be, the centrifugal advance were it's supposed to be, the install height where it's supposed to be, the oil pump drive in the correct location, and will virtually eliminate the problems with the Jeep version of the Motorcraft/ DuraSpark ignition (namely, small, unvented distributor cap, short rotor, old style plug wires, and the factory canister coil)

    The upgrade includes:
    -Larger & Taller Distributor Cap, spreads the terminals out and cuts way down on cross fire and chain fire.
    -Taller Rotor, keeps the spark energy from jumping from the rotor to the distributor chassis (Ground) inside the distributor. Cuts way down on misfires.
    -Better cap terminals, Accommodate the 'HEI' style plug wires, and don't hold moisture or debris in the distributor cap.
    -TFI ignition coil, is about 1-1/2 more potent than the canister coil.
    (The TFI coil will increase all of the important factors of spark energy, Voltage, Spark Duration and Amperage.)

    For a world class- High Performance ignition capable of 15,000 RPM, you can use an MSD 6 series ignition module, WITH ALL OTHER COMPONENTS BEING STOCK, and your ignition system will beat any other ignition on the market.
    (If you can prove that any other $130 improvement will do a better job, I'll buy it for you.)

    You are using a distributor that was designed and tested for your engine.
    You are using a distributor that with the upgrade parts coming from somewhere like MSD, the upgrade is 50 State Emissions Legal, and CARB certified.
    All upgrade parts can be bought over the counter at any discount auto parts store in a pinch, no exotic parts of any kind used in the basic upgrade.

    Easy for an amateur to do in the drive way in under two hours, even if you rode the 'short bus' to school...
    (Ignitions For Dummies...)

    Look for $100 for the basic upgrade (performance well above the GM HEI),
    And around $200 for the MSD version of the upgrade parts (Emissions and CARB Legal)
    The basic MSD 6A module runs about $130, and the top end, the MSD Off-Road Module is about $240.

    The GM HEI ignition, and ALL of it's clones are from a defective design to start with.
    The GM HEI was designed in 1966, went into limited production (with points to trigger it) in 1972, and was used in all GM vehicles by 1974 with an electronic trigger.

    GM could never design out all of the defects, so the entire Coil-In-Cap design was scrapped. GM now uses an ignition very similar to the Ford ignitions.

    The GM HEI was never accurate enough to adequately trigger a computer system (or high performance engine).
    The GM HEI is NOT designed to work with your engine.
    The GM HEI is NOT Emissions or CARB legal in any state.
    The GM HEI / Hybrid For Jeep is comprised of mismatched parts, plugged into an engine it's not supposed to be in, and 9 times out of 10, is supplied by power wires too small to adequately feed the ignition.

    Changing over to a GM HEI system will require either an investment of about $400-$600 to purchase the distributor and support gear, and it will require scrapping the entire stock ignition system, and starting from scratch.
    (I have not seen one single web site yet that installs the GM HEI correctly.)

    A word about aftermarket ignition parts...
    The most common mistake most people make is to think that something in a flashy box, or with a racy name and high price tag is 'Better' that stock parts....

    MSD 'Blaster' and Accel 'Super Stock' ignition coils are exactly the same thing...
    Factory type premium coils with pretty paint and a sticker, .... and a doubled price.

    HEAR THIS...

    (All are manufactured in the same factories.)
    ONLY MSD IS 50 STATE EMISSIONS AND CARB LEGAL. They have done the testing and received the certification.

    (All are manufactured in the same factories.)
    ONLY MSD IS 50 STATE EMISSIONS AND CARB LEGAL. They have done the testing and received the certification.
    Borg-Warner, AC Delco, Motorcraft, and a couple of others make ALL of the premium and factory stock ignition coils in the United States, so no matter what brand you buy, you are getting one of about five major manufacturers.
    (If you buy the 'Economy import coil, then you get what you deserve...)

    In most cases, the premium, lifetime warranty store brand of plug wires will work just fine with stock type ignition systems.
    The 'Hellically Wound' type of wire is ppreferredover all other types.


    For High Performance Ignitions, As Of The Writing Of This,
    MSD Makes The Finest Plug Wires Available. The 8.5 MM wire sets are the lowest resistance, lowest noise (both RF and EM), and the highest voltage with the best insulation that I've ever tested.
    At about $60 to $80 a set, they are NOT cheap, but will last a very long time, and are well worth the money if you need them.

    * * * * * * * * * *
    Answers to LEVEs Questions...

    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 *** 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 :o:o:o:o 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 ****ed 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 :o:o:o:o 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 ****ed!

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

    [ September 05, 2002, 11:39 AM: Message edited by: Sycho15 ]
    1975 J20 401/TH400/BW1305

  • #2
    dang sycho,

    You back up that punch huh?
    Thanks for the research I owe you
    Texas Full Size Jeep Association


    • #3
      for the money and simplicity, a hei is still better in my book.if you are going to race them, go for pure aftermarket, but come on guys, its a 258 six.
      1973 j-truck<br />dead 258--304 coming to life as we speak


      • #4
        I replaced the stock presto-no-light in my rig with the tfi upgrade powered by msd. big improvement. ran it for a year till I roasted my msd box, then replaced the whole friggen thing with a d.u.i. distributor from performmance distributors. I guess that my old 76 401 don't know that it wasn't designed to work with a h.e.i. distributor, but it runs better than it ever did with the t.f.i. and I have been running this setup for two years as a daily driver with no problems and no maintenance...........phil
        76 Cherokee W/T 401


        • #5
          no its a 230 tornado...and ill git it to turn 6 grand yet.....once i replace the motor from it blowing at 5
          64 Wagoneer 283 SBC
          50 truck
          63 J-200 Truck -- help bring home

          Please, if you believe in the power of prayer, God and Jesus Christ... I beg you add my relationship with Heather Boyd to be reconciled to a new, stronger than ever, wonderful marriage ... to your prayer list and remember us daily.

          And now that im getting Divorced .. i want to work on it , but no one else does -- ^ -- Heather, please leave your affair with Josh Smith and come back to the father of your children


          • #6
            if that dont deserve to be put in tech nuthin does
            78 4door chero base model as it gets 258 3 speed d44 f/r


            • #7
              Very informative. I think I'll be doing the TFI upgrade.


              • #8
                [QUOTE]Originally posted by Sycho15:
                [QB]Everything below came from searching the Off-Road.Com forum for posts about this topic by a member called TeamRush.

                (1) A lot of you are too young to remember, but points had to be adjusted about every 3,000 miles max, and replaced every 10,000 miles, or you got to walk.
                (and it always seemed like it was at night in the rain when they quit!)

                (2) For a world class- High Performance ignition capable of 15,000 RPM, you can use an MSD 6 series ignition module, WITH ALL OTHER COMPONENTS BEING STOCK, and your ignition system will beat any other ignition on the market.

                (3) 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?

                (4) Do you think I make this stuff up?

                (1) It seems that I live in the dark ages as I'm still using points. I use quality parts ( Blue Streak ) and don't have any problems. I did recurve my distributor on a machine to get the most out of it and for my needs from idle to 3500 - 4000 RPM it works just fine. It takes me around 20 seconds to reset the dwell and under 5 minutes to replace the points and condenser. And so far I haven't had to walk home in the rain.

                (2) As my engine never even sees 5000 RPM the need for a world class 15,000 RPM ignition system escapes me. I don't know you and no slight is intended but are you an MSD retailer?

                (3) No I can't, I did find a combination that works for me and I'll stick with it.

                (4) As I don't know you I'm not sure if you do or don't.

                There is some good information here but where did you get all the data? It is good reading and gives you something to think about though.
                41 MB<br />46 CJ-2A 307,T90,D18,27,44,4:27\'S<br />64 Traveler, 350,sm465,np205,44\'s w/4:88\'s, spool, 34X9.50 TSL\'s,3\" factory lift, Line-x interior, PS, Dual Optima\'s, custom overhead console,Warn XD900i,custom bumpers<br /><a href=\"\" target=\"_blank\">Overhead C

                STOLEN! Dana 300 Twin Stick


                • #9
                  cant say i disagree with any of the design specifications but what i can say is this - in the ten years of professional auto repair business i have personally changed tfi modules and triggers at least 10 times more often than HEI designs - where they get the idea that HEI modules have inherent problems is beyond me....and according to the GM tech school i went to HEI is good for 60k volts, 5,500 rpm and 500 horsepower. either way they are both fine upgrades over points
                  Jeff - 74 Cherokee S 401/400/QT - basically stock


                  • #10
                    I'll say this once, and once only! I've had and used a Jacob's system on 2 vehicles for a total of 4 years, before it died, it paid for itself.

                    I'm using the TFI mod, now, and am happy with it, and since I bumped up the supply to the pos side of the coil to a constant 12v, I've been even happier.

                    I've changed, and have seen problems with just about all the ignition systems available, each has it's good points and bad. Most work well enough to make an engine run, but ALL do the same thing, and that's make a spark that will jump a SMALL gap. The cam, and timing chain provide the timing, nothing else.
                    Jeep Grounds
                    RRV Homepage
                    Texas Full Size Jeep Association
                    1987 Grand Wagoneer
                    AMC 360/TF727/NP229
                    1999 Wrangler Sport

                    ?Freedom is never more than one generation away from extinction? by Ronald Reagan.

                    Formerly of DFW/Gun Barrel City, TX - eventually to return...


                    • #11
                      Aaron (TeamRush) owns some sort of race-car business, building ignition systems for all sorts of applications.

                      I've done both HEI and TFI conversions to my Jeeps and they both ran just fine. I'll probably do more conversions in the future, and I'll just recomend whatever is easiest. If replacing the distributor is necessary, than I'd go with HEI. If the Motorcraft/Duraspark ignition is present, I'll upgrade to TFI.

                      My Wrangler with HEI would turn 5000rpms with no problems, and the Postal which previously had TFI...well, it doesn't have a tach
                      1975 J20 401/TH400/BW1305


                      • #12
                        I dont know about that. What about all the old GM cars/trucks that are still running fine with it? I dont think it could be that big of a piece of junk.

                        I'm sure the duraspark when properly setup works great though. I've always liked Ford products they seem to be well built. Only thing is it has alot of wires.

                        I'm running the prestolite with tfi coil and it works good. Even have a spare new module for it so I'll run it till it dies. Dont know what I'll go with for new ignition probably duraspark.

                        I wonder how Dennis(scoutgrl) has made out with his idea of using a dual mode duraspark module to vary the timing from in cab.