In the last installment I discussed some of the early transistor ignitions that were offered in the 1960s. GM, Ford and Chrysler all used similar ignitions where more efficient and faster switching transistors supplemented or replaced the mechanical points. However, adding transistors to a standard ignition wasn’t the only way to improve upon the weaknesses of the breaker-point ignition. General Motors Delco-Remy division didn’t put all of its eggs in one basket, and actually made a second electronic ignition system during this time, but one that used a different concept all together.
Most automotive ignitions are inductive ignitions. This means the ignition relies on inductance between the primary and secondary windings in the coil to create the high secondary voltage. As discussed in part one, as RPM’s increase, there is less time for the coil to charge, and the result is the ignition energy is reduced at high RPM. Nevertheless, this isn’t the only way to produce a high secondary voltage. Another concept is capacitive discharge ignition, which has been around since the beginning of the century. However, it was the advent of the transistor that made this ignition system much more palatable for use in production vehicles. Commonly called CDI or CD ignition, Delco-Remy released its transistorized CD ignition for 1967 Oldsmobile and Pontiacs.
The key concept behind the CD ignition is that it uses a capacitor. A capacitor is a component that is used to store an electrical charge. Inside the CD ignition control box is an invertor and transformer which charge up the capacitor within. The invertor draws power from the battery and the transformer steps up the voltage to about 300-400 volts. This is stored in the capacitor. When the primary circuit is opened, the capacitor discharges its output to the ignition coil’s primary side very quickly. This induces the secondary circuit, which further steps up the approximately 300-400 volts by a factor of approximately 100 times, and the spark plug fires.
A big advantage of the CD ignition is that the ignition energy is created by charging the capacitor rather than the coil. A capacitor can be charged in a fraction of the time it takes to charge a coil, which means that a CD ignition will not lose energy as quickly at high RPM like an inductive system. In addition, some CD ignition systems are powered directly from the battery by large heavy gauge wires for minimal resistance. The higher voltage from the capacitor is put into the coil, which acts as a step up transformer, results in correspondingly higher secondary voltage, about 100 times the primary voltage (depending on the turns ratio of the coil). This means that the spark produced is significantly stronger than that of an inductive coil. As a result some CD ignitions, like Delco-Remy’s, used a specialized coil.
Like a transistorized inductive ignition, CD ignition can be triggered by mechanical breaker-points or by a magnetic pickup coil assembly. If triggered by a set of points, very little power actually goes through the points resulting in very minimal wear as they are simply used as a triggering mechanism. The ignition’s electrical current bypasses the points, and is supplied from the battery to the ignition control box (which contains the capacitor) to the coil. The end result is significantly reduced breaker point wear and maintenance. The regular production option version of the Delco-Remy CD ignition, however, used GM’s advanced magnetic pulse distributor. With this, maintenance was reduced even further, and the ignition would stay in tune far longer. Delco-Remy also sold the CD ignition in the aftermarket as a retrofit kit and offered a version that allowed it to be triggered by a breaker-point distributor.
Typically a CD ignition has significantly higher secondary voltage than a standard breaker point ignition, and the end result is a far stronger spark. In fact, it was so strong; GM and other aftermarket CD ignition manufacturers, boasted that it would fire a fouled or fuel soaked spark plug. The high voltage and the ability to fire fouled plugs, meant that spark plugs would last longer and the car started better in cold conditions. Further because the quick charging capacitor could fully charge in much shorter time, CD ignition was far better at high RPM.
The Delco-Remy Capactive Discharge ignition was available on Oldsmobile and Pontiacs as a regular production option. In appearance it looked very similar to the Delco-Remy transistor ignition, consisting three specialized components, a control box, a special red coil and a magnetic pulse distributor. However, it should be noted the more complex CD control box was considerably larger than the transistorized amplifier.
The 1963-66 Pontiac transistor ignition, option 671, was an inductive transistorized ignition as described in the previous article. For 1967, despite the lack of name change, the Pontiac transistor ignition option was revised to be the Delco-Remy CD ignition. It was a $114 option and only available on premium fueled engines without an AM/FM radio. Oldsmobile also added the same CD ignition to its option list for the 1967 model year, calling it the “Ultra-High Voltage” or UHV ignition. It cost about $100 and was offered in 1967-68 under option code K-66 on Oldsmobile 400, 425, 455 engines. Some sources claim it was also available in 1969, but I couldn’t find an option listing for 1969.
The Delco-Remy CD ignition was relatively short lived. Like the Delco-Remy transistor ignition it reduced maintenance but it required more costly components, was relatively expensive and probably few outside of serious high performance drivers noticed any significant difference. It could also be argued the added complexity of CD ignition made it less reliable than other choices. This ignition offered much stronger spark with a higher voltage, but the trade-off was that it was very short in duration. So while this is a great ignition system for a high revving, rich running, muscle car engine, it is not the best choice for an engine that needs complete combustion to minimize emissions. Longer spark duration became more important as emissions regulations moved to the forefront. Despite little use in production cars, aftermarket CD ignitions were popular upgrades in 1960’s and 1970’s. Today they remain popular for the muscle car crowd, in particular MSD branded systems.
With new emission regulations beginning in the late 1960’s, manufacturers needed to come up with a better ignition system to help reduce emissions. While past electronic ignitions were more focussed on high-performance, the focus shifted to meeting emissions requirement. The big advantage of an electronic ignition was that it was more accurate, stayed in tune longer and reduced maintenance. This also helped ensure an engine burned cleaner for a longer period. First to develop a mainstream electronic ignition was Chrysler. Introduced in May 1971 on 340 manual powered cars, it became a regular option on some 1972 Chrysler products. For 1973, all Chrysler products had the new Electronic Ignition System (EIS) as standard equipment.
The Chrysler EIS was similar to the Delco-Remy transistorized ignition. It eliminated the breaker-points in the distributor, and used a magnetic based pickup in place of breaker points and rubbing block. The ignition was controlled by an external device which contained the transistors. Chrysler called this the electronic control unit or ECU rather than an amplifier. From the outside, the distributor didn’t appear to be significantly different but inside was a different story. Below the rotor and attached to the distributor shaft was a reluctor, replacing the traditional rubbing block. The reluctor had 6 or 8 spaced ridges, depending on the number of cylinders. Mounted stationary in the distributor was the pick-up coil assembly.
Like the Delco-Remy distributor, as the reluctor rotates, one of the ridges will pass the pickup coil and it will produce small positive voltage. When one of the spaces passes the pickup coil, a negative voltage is produced. The end result is a small AC voltage. When the positive voltage begins, this will signal electronic control unit and the fast switching transistors will open the primary circuit, which then induces the secondary circuit and the spark plug will fire.
This ignition was a big improvement over the old breaker points, allowing for more precise ignition timing, less chance of misfire, improved starting and high RPM performance while reducing maintenance requirements. However, this system still restricted the power to the primary circuit. Chrysler continued to use a ballast resistor. It was different than the previous resistor, in that it had dual roles. It reduced the voltage at to the primary circuit with the same 0.5 Ohm resistor as the Chrysler breaker point ignition, while a second side of the resistor was a 5 Ohm resistor that protected some of the electronics in the ECU. Since the resistor reduced the power to the ignition coil with the same 0.5 Ohm of resistance as the breaker-point ignition, it meant that this ignition had the same overall amount of energy to the previous breaker points system. However, this saved production costs as the ignition did not require a special coil. The Chrysler EIS was revised over the years, with different control boxes variations, and a change back to a single ballast, but the system still had the same fundamentals.
Back at GM, we know that the original Delco-Remy transistor ignition dated back to the early 1960’s and was last used on 1971 Chevrolet high performance engines. On the other hand, Pontiac who’d been a pioneer of electronic ignition hadn’t offered any electronic systems since the late 1960s when the CD ignition left the option list. Delco-Remy designed a modern ignition to replace the transistor ignition and Pontiac ended up being the division to use it. This new ignition was called the Unitized (or Unit) Ignition and it incorporated several design features to help address issues from the original transistor ignition.
The extra complexity of the Delco-Remy transistor ignition was one area that engineers addressed. The engineers decided the best solution was to combine all ignition components into one “unitized” component, hence the name Unitized Ignition. This system consisted of a specially designed distributor which contained magnetic pick-up coil unit, a mechanical advance mechanism, an ignition module and the coil. It sounds quite similar to the HEI distributors that GM would release later in the decade, but there was one major difference. The Unitized ignition wires were a one piece specialized part. Meaning you couldn’t just replace one wire, you had to buy a proprietary set. It also used a specialized distributor cap and ignition coil, all of which were significantly more expensive and not found in the aftermarket.
Another enhancement with this ignition was that it provided 12 volts of power to the primary circuit – there was no resistor used. With no resistor, the Unitized Ignition energy was further increased. The higher primary voltage results in a higher secondary voltage. The previous Delco-Remy transistor ignition used a resistor on the primary side of the ignition, meaning it reduced primary voltage and the overall ignition energy. However, the resistor used on the Delco-Remy transistor ignition was less restrictive resistor than the breaker-points ignition.
The other major advancement was the reduction in size of the amplifier, which GM renamed the ignition module. The module was made significantly smaller allowing it to be mounted on the distributor housing. The Unitized Ignition eliminated the complex wiring harness with multiple connections of the transistor ignition system to only one 12 volt connection to the distributor. Largely, the Unitized Ignition was really just further refinement and evolution of the original magnetic pulse transistor ignition, bringing it one step closer to the HEI system.
The unitized ignition was first made available on 1972 Pontiacs, but it was not overly common. It was initially a mandatory option for the 455 HO engine, but Pontiac made a change partway through early in the model year making it a regular production option, listed at $77. It remained on the option list for 1973 and 1974 until it was phased out and replaced by the HEI system.
Ford was the next manufacturer to introduce a mainstream electronic ignition. First used on late 1973 Lincoln engines, Ford introduced what they called Solid State Ignition. All 1974 California cars received this ignition, along with 49 state cars powered by 400 and 460 engines. In 1975 the ignition became standard on all Ford cars. Like Chrysler, this ignition’s primary purpose was to help reduce emissions.
The Ford ignition was very similar in design to the Chrysler ignition. It too used a distributor with a magnetic pick and an armature (Ford’s name for a reluctor) and even the internal components looked very similar. The ignition contained a large externally mounted control box, which Ford called a module. This module contained the transistors that were triggered by the AC voltage of the distributor pickup. Like Chrysler, Ford kept a resistor in place, albeit a resistor wire, and the resistance value was the same as the breaker point ignition. This means the overall ignition energy was not increased over the old breaker point ignition. Initially this allowed for reusing the same coil, but a running change for 1975 used a new ignition coil with lower primary resistance which utilized a special connector.
The Ford ignition system essentially functioned the same as the Chrysler EIS. It too improved starting performance, emissions and high RPM performance while reducing maintenance. However, Ford being Ford, resulted in its engineers changing the ignition on an annual basis from 1974-76. Over that three year span Ford redesigned ignition module each year. And although the systems appeared identical all of the wiring was also revised each year. This meant that each year from 1974 to 1976, Ford used a specific module and wiring harness, none of which interchanged with other model years. This ignition eventually became more refined and consistent, evolving into the Dura Spark ignition.
As time went on, it became apparent that while electronic ignition wasn’t overly popular as an option, but it did become a necessity for producing cleaner burning engines. In the final installment of this series, we will look at the final mainstream electronic ignitions from Ford, GM and Chrysler from the mid to late 1970s. Ford would develop its Dura Spark I and II systems, GM would develop its HEI system and Chrysler EIS was further changed with its Lean Burn system becoming the first to incorporate some basic computer controls.
A special thanks to Daniel Stern for supplying some of the research material on vintage ignition systems.
Automotive History: Electronic Ignition – Losing the Points, Part 2
Automotive History: Electronic Ignition – Losing the Points, Part 3
Thanks for this second term of Ignition School. I can remember as a kid reading magazines that referred to a CD Ignition as a performance booster. I had not understood that a CD system was different from those other early transistorized systems. Now I know.
I note the Oldsmobile name of “Ultra High Energy”. Olds must have liked Ultra because the air cleaner of the 330 4bbl in our 64 Cutlass proclaimed “Ultra High Compression”.
This was also helpful in finally being able to visualize a reluctor. This was the device that Ford used in a vehicle speed sensor in the differential of my 94 Club Wagon. I don’t think I have ever removed the distributor cap of any car that did not use points.
Thanks JPC. I noticed that too with Olds’ use of “Ultra.” There were lots of aftermarket CD ignitions during this time, far too many to cover in this series. CD ignition does have its advantages as I explained, but ultimately their additional complexity seems to make them less reliable overall.
It’s interesting how each manufacture used a different name for the “reluctor.” They are used in other applications, such as wheel speed sensors. On the back of the old style hub/rotor combos you would could see them for the speed sensors. Interestingly, even though each manufacture had their own pick-up coil design, we know today that that the GM, Ford and Chrysler pickups all can work properly with a GM HEI module.
Thanks again for this very detailed history that filled a lot of gaps in my knowledge/memory.
Same here – it’s a series one can really dwell on!
Yeah, feels chilly in here…about 30 degrees…..turn it in till it starts to miss, then back it out half a turn. Being a GM driver in those days (over my dead body now, though), that was how it was done. I never messed with a Ford or Chrysler distributor.
Let’s just say the timing of the post was spot on!
Here’s a photo showing the aftermarket Delta Mk 10 aftermarket capacitive discharge ignitions. The terminal strips connected to the coil terminals for easy installation. The Mk 10B had a bypass switch that returned to regular points ignition….or to an original equipment electronic ignition, like the Chrysler system, that used a regular ignition coil. The Deltas passed very little current through the points, which were used as the trigger. So points didn’t erode, though the rubbing block still would wear.
As mentioned in my comment to the prior electronic ignition article, these units passed a very high-voltage pulse to the coil…in the Mk 10B, multiple pulses for a longer-duration spark. The downside was that with factory stock coils, the very high voltage could cause internal arcing and coil failure. The first symptom was a miss under acceleration. If you had a Mk 10B you could use the bypass switch to go back to standard ignition, which would usually clear up the problem temporarily by reducing the arcing, but you were well-advised to go buy a new coil, most preferably an upgrade one that could withstand the high voltage.
When working properly, these systems fired even fuel-wetted and oil-soaked spark plugs. They were also marketed in partly-assembled kit form by Allied Radio and Heathkit.
It seems there were lots of aftermarket CD ignitions during that era. I have a few old Peterson’s books from the late 60’s early 70’s that covers off several aftermarket options. Obviously some aftermarket ignitions were better than others. Delco-Remy’s was designed well enough that they realized a coil specific to CDI was required to work reliably. All of Delco-Remy’s canister coils for the CD ignitions were red to help identify them from a conventional coil.
I built the kit version of the Mark Ten and installed it on the LA V-8 in the Dodge Van. The inverter circuit made constant noise. There really wasnt any noticeable improvement in performance. I ran the truck at low rpm most of the time and didnt operate in an arctic climate. Point life was the only real benefit. Never burned up a coil.
My Dad and I built the Radio Shack kit version of this ignition back in 1973 for our ’73 Country Sedan. Once the gas crisis hit, my Dad thought that it would help it get better fuel mileage. Not sure if it did, we didn’t have it hooked up for long, after an ignition coil failed on a trip back to his hometown where we had to be rescued by a relative, my Dad bypassed it and we later took it out of the car…I still have the box (mostly keep it for the big heatsink, though I’m not sure what I’d do with it.
Another outstanding contribution. I don’t think technical histories with this level of detail are available anywhere else. Thanks.
Thanks everyone for great the feedback on the article. It is much appreciated as these technical history’s are a bit of a labor of love. A lot of this stuff I dug up a few years ago when I was trying to decided on what type of ignition I was going to use on my car. I wanted to examine all ignition options in depth to understand them at the fundamental level.
I learned the concept of capacitive discharge at a young age and the hard way. 🙂
This is another of the few standout CC articles I have bookmarked for two reasons: 1. For future reference, and, 2. To read over a few more times because there is too much good information to absorb.
This is a great read.
And now for the Porsche angle that probably no one has been waiting on. They introduced theirs (by Bosch) in 69, also requiring a special coil. Helped with plug fouling since air cooled S engines needed really cold plugs. They have around 450 volt output from the CDI unit. Easily destroyed if terminals were reversed during a jump start. These lasted a long time with many still in the same car. They are dated so you can tell. Open one up and it looks like a kids Radio Shack project at first. Then you notice the good solder and assembly detail. You can even repair them if you can read a schematic.
Many engine builders report NO increase in measured combustion pressures using MSD or other aftermarket CDIs.
Little maintenance needed except the Bosch rubbing block grease is hard to find today in the original formulation but high temp brake caliper assembly lube works well. Need the 100% silicone type. We get the small Porsche can at work, around $60! Must be made from distilled mermaid tears….
Yes, I recall reading about the Bosch CDI used on Porsche some time ago. It seems to have significantly more voltage output than the Delco-Remy system. I also remember reading some online threads several years ago on Porsche forums discussion restoring the Bosch systems or retrofitting an MSD box. There was some great technical discussion, and from what I recall, other than being significantly cheaper to use an MSD box over restoring a Bosch box, there was no significant advantage. MSD’s mutli-spark doesn’t seem to offer any significant advantages over the Bosch setup either. And many argued that the MSD box was lower quality and not as reliable.
I think a proper CDI ignition requires a coil that is designed to work with the CDI. Those kits that reused the stock type coils were probably just done that way to reduce cost and save money up front for those retrofitting. Any system that is worth its salt has all components engineered to work together, like the Delco-Remy or Bosch System.
A little late to the party here, Vince, but another great one here. I started to read this yesterday, but got sidetracked here at work. So this morning I finished reading it over my coffee before work.
Reading it on my iPad, when I got down to the schematic, I had yet to scroll down to the caption below the picture and started warming up my drafter’s eye by looking for what was different between the ’75 & ’76 Ford.
I immediately spotted the swap between 7 & 8 (purple and black, respectively). I however completely missed the removal of 6 (blue) on the ’76 schematic. Perhaps my coffee was not strong enough, or had not yet taken effect.
Looking forward to part 3 when we get to my old ’79 Fairmont Futura’s set up! ;o)
Also worth mentioning: in the late 1970’s there was quite a cottage industry building add-on electronic dwell-extender boxes. The points became a trigger and the circuitry electronically increased the dwell angle. I knew someone who made one such unit in his basement and sold them by mail order. He did a brisk business for a while, but it was a crowded market (even Radio Shack sold a kit version).
Thank you for continuing this very detailed and informative history. I think I almost understand much of it, and am passing along a recommendation to read this to others who could benefit. I was pretty good with a dwell-tach (still have my Sears Craftsman Engine Diagnostic box someplace), screwdriver and points file in the day, but didn’t really understand how all those electrons got moved around. Like others, I just assumed that when the points closed the spark plug fired. Oops.
Question: do those Pertronix after-market kits just replace the physical points with an electronic trigger, or do they also boost the voltage? If the former, the recommended upgrade to a GM HEI would make good sense. If you (or your stylistic sensibility) can fit that big distributor cap under your hood.
“Question: do those Pertronix after-market kits just replace the physical points with an electronic trigger, or do they also boost the voltage?”
My Pertronix worked just fine with the stock Ford coil, and the coil lasted the entire time I had the Pertronix on it, so my WAG is no, or not much.
Thank you for the kind words. Yes, you are correct. The Pertronix simply does the job of the rubbing block and points. It also acts as the ignition module and controls when the ignition coils primary circuit is interrupted.
A Pertronix Igniter module doesn’t increase the ignition energy over points. The coil still gets the same amount of power as it would in a points setup. It simply controls the coil. It’s main advantages are that it offers stable timing and less frequent timing adjustments.
An HEI is definitely a much better ignition than a Pertonix Ignitor conversion. You’ll see in the next installment when I cover some of the reasons that the HEI module was the most advanced of it’s day. Don’t forget, like we’ve already seen at CC with TBM3Fans’ Dodge Polara, HEI modules can also be adapted to other ignitions. Both Mopar and Ford electronic distributors can trigger a HEI module. So there isn’t always the need to run the supersized HEI integrated distributors.
That Unitized Ignition wire set!! Can you still get those?