There’s a sturdy argument to be made that GM’s HEI (High-Energy Ignition) is so damn good because GM were so damn fixated on being so damn cheap. Wait…what? How does that reckon? Simple: it was less costly than anything else they could’ve done.
US automakers made some respectable efforts to harvest the lowest-hanging fruit when serious emissions regulations started taking effect in the late 1960s and early ’70s. Chrysler, having been the first(?) automaker to experiment commercially with electronic ignition—they offered a Motorola transistor ignition system as a fleet-only option on certain 1966 models—went on to be first to market with a –pointless– breakerless electronic ignition system, a homegrown one optional on ’71 V8s and standard on all engines from ’73 on. The main goal was to eliminate breaker points, which begin deteriorating the moment the engine is first cranked. Even with perfect tune, brand-new points and everything, at the tailpipe you’ll hear misfires as chuffs and splutters mixed in with the exhaust note, every one of which is a slug of unburned gasoline—more and more of them as the points wear and burn and the condenser degrades. So a system with less and slower deterioration was an effective emissions reduction strategy. Marketable, too! In fact, Chrysler’s electronic ignition was a little zappier, but not much; coils and caps and rotors and distributors stayed cost-savingly unchanged, and spark plug gaps remained small at 0.035″ (0.89 mm). The main advantage was a more durable state of tune.
In the bigger picture, the American auto industry put forth what might diplomatically be called largely a cynical response to progressively stricter emissions regulation. They resented lawmakers telling them what to do, and behaved as though emission control were a silly passing fad not worth putting much serious thought or effort into. They assured each other in selfgratulatory technical papers that the 1970-model cars’ exhaust was squeaky- (and sufficiently-) clean and no further cleanup effort was warranted. And they applied cheap, nasty, hang-on-and-pray strategies to squeak the cars past their Federal emissions certification tests so they’d be legal to offer for sale. Driveability, performance, fuel economy? Pfft! Those weren’t on the test; they went right down the crapper. Besides: Oh, gee, Mr. and Mrs. Carbuyer, oh gosh, your new car runs poorly and guzzles gasoline? Tsk, what an awful pity. Too bad, so sad, not our fault; you’d best run get busy writing to your congressman about it!
So why, then, did GM devise such an excellent ignition system, better than all the others, convincingly the best of its type in the world? Because it was less expensive than upgrading primitive fuel systems and stone-age combustion chambers. Honda demonstrated the latter by making a set of CVCC cylinder heads for a Chev 350; tables III and V tell just about the whole story. In response, GM carried on scornfully yukking about ‘Japanese beetles’. Meanwhile, the improved combustion resulting from a strong ignition system compensated, at least enough to get the cars past the certification tests, for extensive slack and sin elsewhere. Besides, GM were sort of boxed into a corner: they had to work and spend hard to have a terrific ignition system because their catalytic converter development program was cursed, or maybe it was just riddled with incompetence.
Or perhaps, given the connection between GM and Ethyl Corporation who made most of the tetraethyl lead used in gasoline, the GM catalyst program was meant (nudge, nudge) to serve as an exemplar (wink, wink) of the foolish, costly waste of the very idea of cleaning up auto exhaust emissions in general, and particularly with catalytic exhaust treatment. Along with Ford and Chrysler, GM spent a whole lot of money, effort, and time waging legal war on every aspect of the regulations, from their technical prescriptions to their timetable to EPA’s authority to issue and enforce them. One wonders what they might’ve accomplished if they’d put that effort, money, and time into engineering rather than lobbying and lawyering. Eventually they lost those battles; the 1975 U.S. emission standards were going to be the 1975 emission standards no matter how big a temper tantrum they threw about it nor how hard they dragged their feet.
So GM launched catalytic converters for the 1975 model year, trumpeting that a ’75 GM car running on unleaded cost less to run than a comparable ’74 running on leaded, in improved fuel mileage—because the engine didn’t have to be strangulation-tuned so much to meet the tailpipe standard, with the catalyst cleaning up the trash in the exhaust—and in reduced maintenance, because spark plugs and engine oil last longer with no-lead fuel—so do exhaust systems, but they didn’t talk about that. Click this ’75 Chevelle ad for a readably-large version in a new browser tab:
Now, too much raw fuel hitting the catalyst makes it heat up and melt down. And even under optimal conditions there was going to be a lot of raw fuel in the exhaust; the cars had dirty-burning engines equipped with carburetors capable of only very crude, sloppy control over the fuel/air ratio on their best day—and prone to many different kinds of bad days. So the last line of defence against converter meltdown was a super-strong ignition system that maximised the chance of lighting each and every cylinder, each and every time. That system, after a couple of predecessors, was HEI.
Like the Mopar system and similar aftermarket setups—the Hays Magna-Pulse was a popular one—and other automakers’ electronic systems, HEI eliminated breaker points. It went a big step further, though, in that it materially increased the available spark energy and duration: more volts (with a wider spark plug gap) and more amps over a longer time. That did a better job of lighting even difficult (lean or stratified) cylinder charges.
What makes the difference? The Mopar system and others like it use the positive temperature coefficient of a ballast resistor or resistance wire (resistance increases with temperature) to regulate primary current to the coil with changes in engine speed, just like in a points-condenser system: at low engine speed the power pulses through the primary circuit are relatively long, so the resistor heats up, reducing power to the coil so parts don’t burn. Not much spark is needed to run an engine at low speed and load. At higher speeds, the pulses are short; the resistor runs relatively cooler, increasing power to the coil to better meet the engine’s greater needs. This feedback loop works slowly, though, so the coil is incompletely charged during sharp increases in engine load, such as acceleration.
A GM HEI module does not rely on slow thermal coefficients. It is typically based on an integrated circuit which regulates coil current using an internal variable voltage reference, which responds much faster to changes in duty cycle. This gives a much hotter spark during sudden-onset high-demand conditions (acceleration), and less coil heating during low-rpm operation. The IC’s program includes a 1-millisecond “off” time to ensure complete discharge of the coil field during a spark event.
So what’s all that mean, practically? See for yourself in this comparison of ignition performance, shown on a sillyscope, of Mopar electronic ignition versus GM HEI in a Slant-6 engine. The HEI spark is of longer duration, and of sufficiently high power to support a larger spark plug gap (0.045″/1.1 mm is the gap GM eventually settled on for engines originally equipped with HEI) for higher secondary voltage and better combustion in the cylinders:
There are those who come over all Klingon, bellowing and snarling indignantly about how they’d rather die than pollute their [brand] car with [other brand] parts, implying [brand] always only ever has the finest, most bestest engineering and [other brand]’s stuff is always only ever super-poopy. With all due respect to them, that’s kind of nutty; no automaker manufactures all their own parts, and most suppliers sell to most automakers. More to the point, a thoughtfully-done HEI retrofit is a worthy, cost-effective, not-very-difficult upgrade for engines equipped a compatible distributor—and that’s a whole lot of engines. Chrysler, Ford, and AMC used compatible reluctance triggers in their electronic distributors. So did Bosch—ditch the Bosch box and put HEI in a Volvo or Mercedes or Bimmer or VW, open the plug gaps from 0.028″/0.71 mm to 0.045″/1.1 mm and go for a drive!—as well as others. People have even figured how to trigger an HEI module with breaker points—you still have rubbing block wear, but you get the other big benefits.
The quality of the outcome depends on the amount of sweat applied to the details. Most cars not originally equipped with a powerful ignition system won’t dependably feed one properly through the stock ignition circuit, for example, and the resultant voltage drop can make starting, driveability, and dependability problems; a power relay is an easy, cheap, and wise way to address this. Parts selection is important, too; the market is flooded with poor-quality trinkets and junk, from whole distributors down to individual components. Module mount location matters—it has to be well grounded, well heatsunk, out of any splash zone (that under-distributor mount plate is just right for V8s, but not for Slant-6s!), and reasonably close to the distributor.
And it’s fine and necessary to have a distributor with a compatible trigger, but that’s not the whole scope of compatibility. HEI distributors are of very large diameter compared to others. That was done deliberately; a high-power spark is more likely to jump where it’s not supposed to, and a large-diameter cap means greater distance between where the spark is properly destined and where it’s not. One reason why Chrysler—despite their strong expertise and capability in electronics at the time—focused on durability of tune rather than high ignition power: that way they didn’t have to retool for larger distributors, which wouldn’t have fit some of their engines, anyhow. An HEI retrofit on a non-GM car means living with the constraints of a small-diameter cap not really designed or intended for high-power sparks. And today’s best caps and rotors, as bought off the shelf, are markedly poorer than what used to be available; there’s scant money to be made in obsolete kinds of parts any more. Nevertheless, a top-notch cap, rotor, and plug wires are all very important for durable good performance and dependability in an HEI retrofit. Some do-it-yourself work will pay great dividends, as described at great (and tiresome, unless you care) length in threads like this one, which over the course of six pages identifies the issues, quantifies them, identifies theoretical fixes, and develops them to practicability. Never let it be said that auto hobbyists are lazy, unmotivated, or unimaginative!
TBM3FAN’s account the other day of installing HEI on his ’73 Polara inspired this present article. He mentioned having read an HEI swap how-to article on another site; I wonder if it might’ve been mine—maybe or not; there are many. I’ve kept largely silent about OE systems other than Chrysler’s and GM’s, but everyone had one; Ford foisted eleventy-seven “no, no, wait, we promise this one will work!” versions of their Dura-Spark on hapless buyers, AMC bought bits and parts from here and there and called it BID (Breakerless Ignition Distributor), and so on and on. And aftermarket electronic ignition system retrofits are outside the scope of this article, except to say that an HEI retrofit is practically better than most of them, as well as more dependable and less expensive.
Further reading:
• CC Automotive History: Losing the Points Part I · Part II · Part III
• GM’s SAE technical paper on the development and deployment of HEI
Thanks for this helpful description of the many issues involved in our ignition systems. Electronics is not my forte and I had never really understood the basics of electronic ignitions. I went from dutifully replacing and adjusting points to ignoring my distributors once they went electronic.
Your explanation of the differences between the Mopar and GM approaches to electronic systems was especially interesting. As an engineer once said to me, everything is about trade-offs.
Totally. The Chrysler system wasn’t done wrongly or badly, it was designed to meet a different list of criteria in different order of priority.
Wow. Fascinating information.
That said, living in LS-land now as I do, I’m SO over distributors and ignition modules, which like to wave bye-bye with each Spring or Fall, especially the later ones mounted on the intake like final 1st-gen SBCs and 4.3 W V6s.
Posts like this always make me wonder about the trajectory of automotive development in the alternative universe in which car emissions were never determined to be a problem.
Sure, EFI and spark control were already in existence prior to emissions concerns, but where would that have taken us? 1000 hp behemoths the size of a ’72 Polara? Who knows? Thing is, despite (or perhaps because of!) emissions laws, you can buy a 707-hp Dodge that isn’t much smaller than a ’72 Polara!
That is an interesting question to ponder. It’s difficult to answer definitively. We can look at Mexico, where cars were carbureted and took leaded gasoline until 1990, then emission control approaching US stringency was legislated and the 1991 cars had fuel injection and took unleaded. But it’s not a direct comparison; relatively poor countries have a harder time introducing anything that raises near-term costs (to buy a car, for example, or to service it).
And even if we just confine the question to a rich, first-world country, there are a lot of confounding related variables to juggle: does or doesn’t vehicular safety get regulated? Does fuel economy? Whatever the answers to those questions, history shows us very clearly that industry will tend to do only what they are absolutely required to do, unless they can make more money by doing more than they legally have to.
We teeter here on the edge of a big political quarrel about the free market and the public good…probably best if we just acknowledge it’s an interesting question to ponder.
I somewhat disagree on one point, history would also show that nearly all of the technology that makes cars safe, efficient and clean today existed well prior to the late 60s when regulation came into effect. When automakers compete on level ground more R&D gets focused on trying to one up each other. Factory backed motor racing deserves a ton more credit than it gets as well, in fact through homologation practices it was the closest thing there was to automobile regulation before government regulation.
In the US however technology got very stagnant after WWII, with an ever less healthy Ford, Chrysler and independents. Sure there were the occasional odd blips sprinkled in(the Corvair/Y-bodies, Pontiac’s OHC), but for the most part the 1955 Chevrolet remained the technological standard for every American automaker until 1980, all that changed substantially was size of the body’s and engines. GM was too dominant for Ford or Chrysler to invest deeply in technologies they weren’t pursuing themselves, and because the US market was virtually captive GM had no real reason to. This is where regulation became a necessary burden – if GM and Volvo for example were competing for the same customers with the same size dealer network, GM would have had to and would have matched the level of safety Volvo put into their cars, no muss or fuss about it. Regulation in essence artificially acts as that leveler for everything from safety to emissions to fuel economy. US automakers obviously didn’t see it this way though.
At the other end of the spectrum of course is the consumers. No matter what, 1973 broke the inertia of ever bigger engines and cars, and by many accounts even before the energy crisis some degree of downsizing was already in the works(Mustang II, 1977 B-Bodies). Imports were gaining enough strength through the 1970s where they likely have eroded away the US land barge dominance on the same timeframe they died off anyway, more than enough at a rapid enough pace for GM and the rest of the big three to be required to answer(as they did in 1960 with compacts). Also as much good fuel injection did for emissions, its absolute benefits in driveability, performance and economy made it an inevitability.
Clean air aside, I don’t think the unchecked outcome would have been much different than it is today in product, as far as technology goes the carburetor and distributer would still be extinct I think.
Your scenario is definitely plausible, that we’d have pretty much the same car tech, though I think its deployment would be (and would have been) slower and its proliferation lesser. I’m largely onside with your perspective on regulation as a playing-field leveller; it also provides those pushes and pulls the market on its own doesn’t adequately exert in re some public good (traffic safety, air quality).
The thing that really sticks out for me, looking in gross at the late ’60s through ’80s, is the consistent behavioural disparity between American automakers who fought tooth and claw (and lawyer and lobbyist) over just about every regulation, and then eventually complied in spiteful ways, versus the European and Japanese makers who put their efforts and monies into complying in ways that benefitted the owner/driver, not just society at large. Examples abound. Seatbelts, induction systems, emission control strategy, brakes, on and on. Of course there are counterexamples, but.
What an interesting and informative article, Daniel, and thank you for it!
HEI is an excellent system. I don’t know how many times I have seen enthusiastic young men junk their HEI system for a manifestly inferior aftermarket ignition.
Y’welcome, and thanks for the thanks. Yeah, ripping out HEI and putting in an aftermarket system is an easy way to spend big money for a big downgrade. Aftermarket systems have sexy marketing and packaging, and big, juicy claims (and prices), but they don’t have to meet original-equipment standards of dependability and durability.
As I mention below, HEI has a poor reputation for high RPM use, which is unavoidable with a distributor based induction ignition. Guys read Hot Rod magazine and they read this and see all the drag racers running CDI systems (MSD et al.) and think they need them too. CDI ignitions have there advantages, especially at high RPM (I believe NASCAR still uses it), but realistically, most street vehicles will see no advantages over a good HEI system.
Many years before GM HEI and even Chrysler’s breakerless electronic ignition, there were aftermarket transistorized-switching and capacitive-discharge ignition systems that one could interface with ordinary breaker-point distributors. The eventual adoption of electronics from the carmakers themselves made them obsolescent but even when applied to older cars they could be problematic. Some were not durable, suffering from failure of their internal electronics. Others, mainly the capacitive-discharge types, produced extremely high voltages…literally, high-voltage spikes…and relied on the inductance of the ignition coil to damp them out. But with them, the coils of the day often had insulation breakdowns because they were built to withstand transients from ignition points at battery voltage…twelve volts, not dozens or in some cases, hundreds of volts. I know of many users of those “C-D” units who had to replace coils due to no-starts or an intermittent miss. Replacement of the coil solved the problem but often it returned. Restoring the original ignition system made the “fix’ permanent.
About two years ago, when cleaning out my garage and its assorted junk boxes, I found one of those capacitive-discharge ignition systems, a build-it-yourself Heathkit version in its original sealed box. I decided against building it and putting it into my 1963 Corvette, my only remaining car that could still use it, which still has its original 1963 Delco coil. Somebody did take it off my hands and I advised him to use an upgrade coil with it.
Outstanding, and very informative article Daniel, thank you. I was very young when the HEI was introduced, but was already really interested in cars. I remember being so impressed at the time with GM’s various corporate ads introducing the HEI, catalytic converters, greater use of radial tires, and improved efficiency in all their car lines. For me, the marque GM car that best promoted all these improvements was… the ’75 Monza. I was a little kid, but at the time I so much preferred the new Monza over the Mustang II (and the Pacer). GM’s ‘green’ efforts really had a positive effect on me then towards them as a car company.
Y’welcome! In the forthcoming article about catalytic converters I will try my best not to crush your childhood impressions of GM as a company that cared…but I will probably fail.
Lol… Thank you Daniel. Indeed, as I left my childhood, I got up to speed on the frailties of GM all too quickly.
I got offered a vintage build it yourself transistorised ignition kit recently still in the original box with instructions etc, quite a mission to build from the look of it I turned it down and my mate threw it in his rubbish bin, his 66 Hillman has electronis ignition already and starts easily and runs great, I’m still using points condesor system and the car goes fine, its not subject to an emissions test ever so I’ll leave it alone for now.
I got a new UK-built Chrysler Alpine in ’79 and just like my previous car, a BMC “landcrab” 1800 with aftermarket electronic ignition, the weakness was that the distributor cap couldn’t handle the extra power for very long.
Excellent write-up Daniel. I have read some of your articles on HEI ignition conversions and they are good reads. I have been experimenting with different ignition systems over the past few years which have resulted in my doing a lot of research of some the old systemsm . It seems the 1960’s and early 1970’s had a lot of interesting systems that were tried by the big three, kind of like the early days of automatic transmissions.
Delco Remy had a transistorized system as early as 1962, which used a magnetic pulse instead of points as a trigger. I know Ford also had early systems that used transistors and points, where the points had a lower voltage (about 4 volts) passing through to minimize wear. And while most OEM ignitions are inductive systems, don’t forget that OEM’s also used Capacitive Discharge Systems (CDI) too, not just the aftermarket. Oldsmobile and Pontiac each has systems in 1967. It stuck around on the Olds option list until 1969. Vintage Porsche’s also used CDI.
I know you are the expert in this stuff, but I always thought the easiest way to explain the advantage to the GM HEI system was too look at the primary circuits. I think it’s important to state, as those who are not tech savvy may not know this, but on breaker point ignition systems, voltage to the points and coil is reduced from 12 volts to only about 8-8.5 volts. This is done by ballast or a resistor wire and the purpose was to help prolong the point life. The Chryslers electronic ignition continued to use a primary circuit that ran on 8-8.5 volts, allowing it to reuse the ballast and coil from the breaker point ignition (saving them money). Essentially, the module replaced the points, but compared to point ignition there was no more ignition output. Ford pretty much did the same thing (more on Ford later).
GM’s HEI was different, because for the first time the full 12 volts (13-14 volts when car is running) was run through the primary circuit. This combined with a low resistance coil and a module quickly charges to about 5.7 amps (when the modules voltage limiting kicks in) results in significant higher ignition energy. This meant a longer hotter burn at the plug and resulted in more complete combustion – reduced emissions.
Here is a simple comparison of the total energy:
Chrysler Electronic Ignition:
8.5 volts x 3.5 amps = 29.75 watts
GM HEI
13.5 volts x 5.7 amps = 76.95 watts
It was also my understanding that the HEI module charged the coil much quicker than say compared to a Chrysler electronic ignition system. We have to remember as the engine RPM increases the time between the coil firing is reduced. However, the time for a coil to reach full charge is constant. At some point, the RPM becomes too high and the coil will not have enough time between firing to reach full charge, resulting in the ignition energy falling off. From what I have read the Chrysler systems were started to exhibit this at lower RPM compared to the GM HEI.
The GM HEI system had a much shorter time for the coil to reach full charge. Of course though being an induction ignition, it still has its limitations, which is why HEI has a bad reputation for high performance/racing use. This is why people add CDI ignition setups, like MSD, because capacitive discharge ignitions, unlike induction systems, do not lose their energy at high RPM (since the ignition power comes directly from the car’s battery to the capacitor meaning dwell doesn’t become an issue). Of course CDI ignitions have very hot but duration short sparks, which isn’t ideal for complete (clean) combustion.
I get your point about the catalytic convertor and the real motives behind them. Yes GM certainly could have improved its poor combustion chambers of the time, but even Honda eventually had to add convertors too. And yes, GM’s bead catalytic converters were awful, but eventually we got some decent ones. When looking at GM Rochester Q-jet carbs, the 1973-1974 carbs were leaned out so much to meet the emission standards that the drivability was terrible. At least when the catalytic convertors were put on the cars, they finally richened up the carbs enough that they ran half decent again. And it also eliminated many of the Rube Goldberg emission devices that the manufacturers were using in the early 1970’s.
For instance, my ’76 Chevy 350 has EGR valve, a heat riser system and a PCV valve, that’s it. Between the HEI ignition and the cat, it didn’t need anything else, and it had great drivability for a car of that era. We have owned several other GM V8’s from this era that also had similar good drivability and minimal emission devices.
On the Ford systems, there is a lot of confusion on those. But Ford did have “breakerless ignitions” that were very similar to Dura Spark between 1974 and 1976. Each year had its own variation and ignition module, but none were actually Dura Spark. Dura Spark and Dura Spark II came in 1977. The previous electronic ignitions used 1.35 Ohms of resistance, just like the breaker point ignitions, meaning no difference in energy. The Dura Spark II was the most common and lasted until 1986. It used 1.10 ohms of resistance, so it would have had a slight increase in energy over the breaker points. The Dura Spark system was only made from 1977-79 and was limited to mostly CA emissions cars. It had no resistor in the system, like GM’s HEI, but the modules proved to be unreliable. The Dura Spark II was more reliable, but today finding quality Ford Modules is tough, which is why many retrofit the GM HEI module into the Dura Spark II (the remaining components are fine). Further, Ford used the same distributor, but with the Dura Spark and Dura Spark II, they use an adaptor that allows for a large diameter cap, similar to GM’s HEI. This can be retrofitted to older Ford distributors as well.
Good points, Vince, and good explanation of the primary-side differences and HEI innovations on that front.
I will largely defer to you on the nomenclature and chronology of Ford’s electronic ignition system; I sort of default to considering them unworthy of much study beyond regarding Ford with contempt for having apparently used car buyers as alpha and beta testers (and gamma, delta, epsilon…) instead of putting forth a whole-assed R&D effort. I do recall a prominent DURA SPARK callout under the hood of my folks’ thoroughly lousy ’80 Town Car, which had the 2nd version (round rather than oblong rotor) of Dura Spark III—the split-level arrangement of cap terminals on both versions of which allowed enormous amounts of spark advance with minimal risk of crossfire. That was clever in theory, but I’m not sure how much of the cleverness translated to practical advantage, and I grew to think very dimly of the system as a whole.
(And yep, it was definitely clever of Ford to use inexpensive plastic clip-on adapters to put large caps on small distributor bodies.)
I remember the DuraSpark modules weren’t all that well sealed in the early days. When you went to pick a part you always got two.
Wow, do I ever enjoy this site. Where else can I get a really good technical explanation in terms I can understand, from two very nice and kind gentlemen?
Amazing!
GROUP HUG!!!
And beer.
Thanks very much Len. This and automotive history are my favourite topics to discuss.
+1 Daniel
Your point on the input current on the GM HEI system is a good one but only tells half of the story. Fact is the coil is a transformer and there is some inherent loss in the conversion. The “E core” style coil is much more efficient so more of the input energy makes it out the HV side.
Yes, you bring up a good point. I just touch on the coil when I mention that HEI uses a low resistance coil, but didn’t take it any further. I also didn’t really get into the “dynamic dwell” of the HEI module either, where it can adjust the dwell time slightly as RPM increases. I thought it was easiest to understand the higher energy aspect by looking at the overall energy from the higher voltage and amperage. Plus the comment was getting little long. I actually have an old article where they compare different coils charged through an HEI module. Using a coil with even 1.5 ohms of resistance results in a significant drop in amperage to only about 3 amps. Using a traditional 4 ohm coil results in not even enough energy to fire a plug.
FWIW, you don’t need an e-core coil with an HEI. You can use a properly specced oil filled canister coil and many do when converting other ignitions to use an GM HEI module.
Yes you can fire a cannister coil with a HEI module just fine, done it on a number of vehicles back in the day.
Very interesting. Our family ’76 Impala would always start whether it was bitter cold or hot, something that could not be said of comparable Chrysler of Ford products. A better ignition. Since I did always follow the leaders as it relates to cars, I became a Ford man. With my first serious car being an ’88 Mustang GT, that used TFI ignition which was a good system when adding an increase in cylinder pressure. I have also played with Duraspark II and usually replace with aftermarket ignition systems. My all orginal Linc ’77 Mark V has Duraspark and the car is a reliable runner, may convert to the “ugly” HEI system though…
I sort of miss tune ups on my old vw vans where I had to set the points, dwell and timing. I don’t miss the $12 for the condenser and another $8 for the points. That and being able to adjust the idle which my modern cars seem to let the computer take care of that function.
So far on my Toyota and Nissan I have only had to replace the cap, rotor and wires. Never had to replace anything else on the ignition. Probably just jinxed myself. My brother tried to get rid of the points and put in a pertronix knock off system in his old van but ended up giving up and sticking with the old points and condenser.
I can relate to missing tune-ups…real ones, not just spark plug and air filter swaps. You really got something for your time and effort; the car ran so much better! Of course, that meant its running condition had deteriorated badly enough for the improvement to be noticeable.
The story I read some years ago as to why Ford dropped their optional electronic ignition shortly after introducing it in 1965 IIRC is that dealers who’s salesmen did sell that option found out that they lost the frequent tune up profits from those customers because their running condition didn’t get so bad that people came in for a minor or major tune. So dealers weren’t happy at all and wouldn’t sell it.
Thank you for a very interesting article. It is a great presentation of technology in an understandable way, reminding me of the glory days of with Ate up With Motor.
I had also suspected that car manufacturers couldn’t avoid the lousy performance of early 70s vehicles. The information here clearly suggests that they simply “preferred not to” when it came to controlling emissions. The data you have referenced certainly bears out the need to do so.
Y’welcome! I never interacted with AUWM, so I don’t know what I missed, but this is clearly a compliment, and I’ll take it. 🙂
Daniel, I have to say I love the way you write about things. You have a very conversational style, which makes getting my head around tricky tech topics much easier. And you anticipate when and where your reader might have problems, and are always ready with an explanation, citation or footnote. Thanks.
»doffs cap, bows« Y’welcome and thanks kindly!
VW added fuel injection to all air cooled engines in ’75, and all water cooled engines in ’77. But VW stayed with points and condenser until the ’80 models when electronic ignition finally arrived. California versions all had catalytic converters. The fuel injection systems were the key component that was missing from the American cars of this period. Always ran the stock points set up in my 70 C10, thought about upgrading but the system never gave me problems.
Thanks Daniel for tackling a subject that’s partly above my pay grade.
Fer sher, fer sher!Gladly.I remember some 35 years ago when I was in vocational school someone brought a late-70’s Chevy pickup to class. The instructor was giving a lesson on HEI, and he had us remove the spark plugs from the truck’s 350. The instructor took a pair or wire cutters and promptly cut all the ground electrodes off the plugs, and had us re-install them. The truck started right up and drove fine! Of course, continued operation would have likely destroyed the rotor and coil (we replaced those parts anyway), but that demonstration made me an HEI believer!
It would have likely fried the module leaving the vehicle dead. That is one of the problems with the HEI system a spark with no good path can kill the module in its quest for ground. I’ve seen more than one person kill the module by trying the old method of figuring out which cylinder is the problem child by disconnecting a spark plug wire. I’ve also seen them towed in with a plug wire that fell off and to a point where it could get a good path.
Very true, but in this case the spark was finding a ground. It was jumping what was essentially a .125″ or better gap! Lots of resistance, but at that voltage not an open circuit. Needless to say the voltage spikes on the oscilloscope near the top of the screen. Continued operation most certainly not recommended, but it did run.
If only I had read this earlier:)
You know two nights ago I was looking through my lighting web sites for something and had one bookmarked Daniel Stern Lighting at which point it dawned on me who you were. Yes, I am slow and dull witted. Anyway your site popped up years ago when I was looking into relays for my headlights and I was gathering information. I eventually bought all the materials to do relays for five cars as I am more of a DIY guy who likes to control the quality of my materials vs. the pre-made sets at the time.
Yah, that’s me! Shoot me an email.
A subject that is completely over my head, but so entertainingly and cogently written I felt like I knew what was being explained. Sort of.
Thanks kindly, Don!
As a Ford mechanic back in the day, I hated to acknowledge GM superiority on anything. Even so, I have to admit to the inferiority of the 1st Ford efforts at electronic ignition.
Before HEI, we Ford guys were proud of the fact that our distributors were so much better sealed against moisture than pre-HEI GM window distributors. GMs might have been easier to adjust dwell on, but more wet weather no-starts weren’t a good tradeoff in our climate. Luckily it was a roadside fix rather than a tow-in. Our tow truck always carried a variety of GM caps.
It all depends on what your definition of inferiority is. When it came to durability and reliability the Ford systems were superior to the GM but behind the Chrysler. Never replaced a single pickup in a Ford or Chrysler but did it many times in GM. Module replacement was much more common too, but some of that was that GM was a victim of its own market share and the race to the bottom on price. So once you got a crappy module and you stuck with crappy modules you’d be replacing them frequently. The coil was also not as long lived as those in the Fords and Chryslers. On the other hand never replaced the resistance wire in a Ford but did more than a few ballast resistors in Chryslers and the Fords had coils that were enough stronger so you were no where near as likely to flood the vehicle on a cold start though the Champion plugs they came with were likely big contributors as well.
I don’t agree that the Ford systems were more dependable than the GM HEI, but probably neither of us will ever have access to the amount and quality of data that would be needed to answer that question, so we’ll have to carry on sticking with our respective anecdotes and impressions.
On Champion spark plugs we agree: junk, junk, junk. Those cheaply, crudely cut threads on them are just the thing for stripping spark plug holes in aluminum heads; the rolled threads on a better plug like an NGK are much less problem-prone. And that’s just one comparison point of many.
Well I was in the repair business starting in 1983 and did a lot of time working on cars of the 70’s professionally and know what I saw and did time and time again.
No dispute there. Confirmation bias is a real thing, though, and so are sample size and selection, and a whole lot of other ointment-flies that make up the giant gap between objective reality and what we think we understand of what we think we’re sure we saw. Not a slam on you in particular; it’s just the pesky difference between how the human mind works and how we’d like to believe it works.
Plain and simple GM vehicles paid the bills for me back in the day and it was seriously disproportionate to the number of vehicles in service, not just because it still included cars from the era when GM was still the sales king by a significant margin. And no it wasn’t because I worked at shops that specialized in GM vehicles. In fact the first shop I worked at was the place to take your MG and Triumphs. The boss left the Jags to the one man show next door who only did Jags and Corvairs.
Later after a couple year stint on the corp ladder I started a mobile auto repair business so a lot of my work was cars that wouldn’t start. Eventually that business morphed into a fair amount of wholesale business where I diagnosed the vehicles that had other shops stumped.
Once the first kid showed up I abandoned the late nights and weekends for a job at one of those shops doing engine replacement, computer diagnostics and drive-ability.
So my experience is based on thousands of vehicles over the 20+ years.
I’m (still) not calling you wrong!
Well, seeing as my 157k mile ’78 302 powered Fairmont still has its original distributor and Duraspark II box you may be on to something.
Chrysler – The well known ballast resistor issue goes without further detailin. Another well known issue was that slight dampness could cause no-start. A common joke was that someone urinated next to the Chrysler, and now it won’t start.
Putting aside the above, and LeanBurn, and dual pickup jobs, overall a reliable system.
Service – Body located module stayed cool and clean, could be changed with a pipe wrench.
V8 Distributors were easy to remove, never stuck in the block.
Simple “no tools” cap removal.
Plug wires of basic construction, many with tough routing paths, were prone to oil attack and crossfire.
Big Block with its front located distributor was great for access. However, the long and winding paths of B engine plug wires were always a mess and troublesome.
Well built long lasting mechanical advance mechanisms.
Slant Six distributor most difficult to access of any common vehicle. Proves Murphy’s law, because of all engines to have a propensity for distributor-drive-gear failure, the inaccesible Slant Six distributor was it.
More random ignition thoughts in a following post.
Depending on where the distributor is located and how easy or hard it is to get fingers alongside the cap with enough leverage, clip-on distributor caps are either better or worse than quarter-turn screwhead retainers.
The Slant-6 distributor is only inaccessible to those trying thoughtless timewastes like putting in points and condenser with the distributor installed. Remove one 7/16″ bolt—it’s clear out in the open, requiring nothing more than a socket wrench with an extension—and lift the distributor outta the block. Takes about 15 seconds.
I guess my more relevant reply is lost. Shrug
Rules to live by:
ALWAYS carry a spare resistor and SS-6 drive gear.
NEVER hit “Post Comment” at CC without saving a copy of your work first.
Over my decades of driving Slant-6 cars, I never carried a spare distributor drive pinion—and never wished I had one with me. Once installed properly they don’t fail very often, and they can’t really be replaced on the roadside anyhow; they have to be cross-drilled as a step in the install process, and it can’t be done on speculation because the exact location varies by distributor. People who make the error of using the single hole that comes pre-drilled in the pinion find themselves replacing the pinion again and again and again.
When I started in the business and the boss put me on a tune up on a slant 6 and was fighting with putting in the points when he came along and said just yak the distributor. Being green I didn’t really like the idea not being confident in my ability to drop it back in and have it fire on the first try. I did pull it and we took it and put it on his old, even then, Sun distributor machine, spun it up and dialed in the dwell.Then we checked the mechanical and vacuum advance while it was on the machine before dropping it back in.
Of course I eventually was able to drop in a distributor and set the timing to within a degree or 2 of my target and have it fire on the first crank.
I was forced into Daniel’s method the time I dropped the screw down into the distributor. After that day I never tried replacing points with the thing in the car again.
Spot on with my experience as with the Ford and GM systems.
Some thoughts, with a focus on what would go wrong, based on first-hand experience with the ignition systems being discussed.
HEI – great concept, unfortunately production world execution wasn’t the greatest. Advance mechanism wear was atrocious; quickly making the drawing-board’s precicise mapping of spark control irrelevant. Said rapid wear of advance mechanism would grind up a fine metal dust that brought on even more problems to the magnetised high voltage under-cap world.
Cap and rotor materials were prone to breakdown and even burn-through which often allowed found-an-easier-path-to-ground ignition failure.
Pickup lead wires weren’t up to the constant flexing caused by advance mechanism movement and caused many “tow in” failures.
Service – Some GM divisions favored distributors located at the cowl, making service a miserable task. Buick and Cadillac get gold stars for front location. Pontiac gets an “E” for epoxy-strength sludge that would accumulate to “cement” in HEI units.
Cap removal required tools and lots fumbling with retainers and wire lead clips.
Great qualty plug wires. The all-or-none retainer at the cap was a hassle.
Module lived in a hostile hidden environment. Tiny retaining screws were easy to break or lose. Recipe for disaster if unnoticed a lost screw found magnetic attraction at the nearby pickup.
Pro – “everything” is in the didtributor.
Con – “everything” is in the distributor.
Repairing advance mechanism and pickup failures (both common) required distributor removal and almost complete tear-down.
No-start diagnosis with “everything” buried within the distributor hidden at the back of an engine was no treat.
I agree with all of the points other than the OE cap and rotor material were good quality. It was the cheap aftermarket stuff that wasn’t designed nor built with the right materials for the voltage potential that suffered from the burn thru.
Ford – Yes, early vehicles with “green” and “black” (grommet color) modules had failure troubles; with the revision to “blue” many of the boxes became life-of-vehicle components. Coils practically never failed. Ditto for pickups.
Despite very hot spark, voltage “breakdown” at any components was very rare.
Plug wires were very robust and followed “clean” paths to the plugs.
A nice Ford feature was that spark would be automatically retarded during cranking. Very helpful when bringing hot large carbureted engines to life.
Serviceability – The common V8 engines had easy access front-located distributors. Distributor’s pickup was easy to service, although rarely necessary. Simple “no tools” cap removal.
Fender-located module stayed cool clean and accessible. If necessary, an inexpensive replacement could be plugged-in roadside, using zero tools.
The mechanical advance mechanism was typicaly trouble free.
A myriad of emmision era vacuum controlled advance/retard schemes were tried. Most ended up with their plumbing rerouted in the field as simple advance mechanisms. Vacuum advance “pot” retained by easy-to-break tiny screws. Hassles, but not issues that would cause ignition failure.
For the reasons I mentioned, of the three ignitions being compared, my opinion is that Ford is best in reliability, serviceability and performance.
What are your experiences?
Yup never replaced a Ford pickup and coil replacement was usually due to corrosion or physical damage, not because of a no start. The Blue grommet modules were very reliable and often lasted the life of the vehicle, I’ve personally had Motorcraft modules on 20-30 year old vehicles. Can’t say they were original as they certainly could have been replaced at the dealer, when they were new enough that they would have likely gone to the dealer.
Of course it’s not that serious, but this is a fun look back. Along with random recollections of what did/didn’t work, it’d be interesting to see some methodology applied here.
Ignition maintenance used to be a big deal. Suppliers would publish guides rating their individual components popularity and sales volume up/dn direction. Some would also recommended stock quantities to keep on hand.
A report based on sales data would give some indication of which ignition parts were the most often replaced. I’d bet that most who were hands-on with the various ignition systems could second guess results.
Anybody still have an ignition parts buyer’s guide in the pile?
Sorry, I’ve already placed my chip on Chrysler ballast resistor for the #1 sales champ. LoL
Unfortunately no, I don’t have any old ignition sheets but yeah the HEI stuff was all AA pop code, meaning that everyone should stock them and stock them deep.
Some thoughts particularly about HEI
1. Ignition rotors in the early years had a lack of dielectric strength. Delco released a bulletin about this. They claimed that electric “punch-through” as indicated by discoloration of the rotor was largely a myth–the discoloration didn’t indicate a failed rotor. The early “black” rotors were replaced with better “white” rotors after a couple years of production. I really liked the Standard Motor Products “Blue Streak” rotors and caps. Expensive, and most of our customers wouldn’t pay extra for a premium product–and the Boss wouldn’t go out of his way to upsell.
2. GM Points distributors had the advance mechanism lubed at each change of points ‘n’ condenser. HEI never, ever got the advance mechanism lubed, because the cap and rotor would go years and years without replacement. There were multiple weight-and-pivot pin arrangements, some with plastic bushings and most without. The plastic bushings were easier to replace than the weights and pivot pins. Thexton sold a “repair kit” with a small fixture where you drilled-out the egg-shaped holes in the weights so that they were round again, and then added new, oversized plastic bushings on the worn-out pins. I tried to buy one of those kits fifteen years ago, and couldn’t find one.
3. The in-cap ignition coil was also upgraded after the first few years of production. The idea that HEI can’t handle high rpm largely comes from these early coils. Early coils have three connections: Red wire, White-or-yellow wire, and the secondary output terminal which connected to the spring-and-carbon button that actually touched the rotor contact. Later coils added a black wire, so that the primary and secondary windings were no longer “siamesed”. There may also be other internal changes to the electrical specs (such as inductance) but I don’t know about that.
4. The HEI module was also upgraded a few model years into the HEI implementation. There’s been on-line discussion from a man I have learned to trust saying that HEI modules NOW have dropped significantly in quality. I have not seen this personally.
5. “Seized in the block”? That’s why GM added a big, square wrenching surface on the upper part of the distributor housing.
6. Pickup coils for HEI are color coded–yellow, blue/black, and clear. The lead lengths are different, and the MAGNETIC polarity is reversed between yellow and the others. Therefore, if using a blue/black or clear pickup coil, the lead wires are crossed before connecting to the module.
7. In-cap ignition coils are also color coded. Some have red and yellow wires, some have red and white wires. The yellow pickup coil goes with the yellow ignition coil. The blue/black and clear pickup coils go with the white ignition coil.
8. The difference in the pickup and ignition coils has NOTHING to do with “high performance” or “more output”. They’re only different in the MAGNETIC polarity, and that’s only important in filtering “noise” that could cause erratic spark when the pickup coil acts as an “antenna” for outside interference. In any event, the spark (electrical) polarity across the spark plug is the same regardless of the magnetic polarity.
I replaced a lot of ballast resistors on Chryslers. Replaced a few ignition modules. The distributors seemed very robust.
Replaced heaps and piles of failed Ford ignition modules, Eventually I learned to scrap the ignition coil with each module change AND inspect the “Bill Cosby” wire harness connectors. The distributors seemed very robust.