Delco Electronic Ignition

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The Delco Distributor and Electronic Ignition System

by Tony RhodesJanuary 2013

THIS IS A PRELIMINARY DRAFT OF THIS ARTICLE. IT CONTAINS ALMOST ALL OF THESCANS OF THE ORIGINAL MANUFACTURERDATA THAT I EXPECT TO USE, BUT ONLYSOME OF THE TEXT. MUCH OF MY TEXT ISINCOMPLETE AND PRELIMINARY. PLEASEEXCUSE THE APPEARANCE!

When I got my 1980 TR7 Spider in 2001, it hadrecently stopped running. It would turn over, but itwould not start. It was delivered to me as a “non-runner” on an 18-wheel auto transport. I had toget a tow truck to get it off the transporter and

bring it to my house. I xed it easily by cleaningthe green corrosion and glop off the contactsof the wire from the distributor to the electronicignition coil unit. At that time I had no idea whatthis electronic ignition was, but it looked old, clunkyand unreliable. It was on my short list of items tobe replaced. It looked like a unique device andit was then 21 years old. I am suspicious of oldelectronics in harsh environments. I was not a bigfan of electronic ignition in general because whenit goes bad, you don’t just run poorly. You don’t runat all. It is hard to diagnose and repair elec tronicignition faults, especially at the side of the road.When your electronic ignition goes bad, it is time fora tow. Points ignition, on the other hand, typicallyde grades slowly with ample warning to allow youto get to a convenient place before it conks out.

I also had a plan to replace the poorly func tioningdual downdraft Weber 32-36 DGEV carbs withsome simple and reliable SU carbs. The SU’son my TR4A work well and are easy to maintain.Plus they don’t have that pesky rubber diaphragmfound on Zenith Stromberg carbure tors. That’s thediaphragm that always rips and makes you run lean.The distributor on the car used vacuum retard, andthe SU carburetors do not have a port for vacuumretard. So when I installed the SU carburetors, Idecided to also install the matching UK-spec Delcopoints distributor. After installation, I found out whythe Brits are keen on replacing the points withsome sort of after-mar ket electronic ignition. It is

nearly IMPOSSIBLE to properly adjust the pointson the TR7. After installing the UK-spec distributorand painstakingly adjusting the points, I swore tomyself that when it became time to re-adjust thepoints, I would install an after-market electronicignition. My foray into after-market electronicignition for the points-type Delco distributor is astory all by itself. Lets just say that the Newtronicoptical pickup for the TR7 is not well designed. Iremoved that ignition almost immediately. In themeantime, I had learned that the clunky-lookingoriginal electronic ignition was in actuality a GMHigh Energy Ignition (HEI) system. The HEI system

is loved by American hotrodders for its simplicity,reliability and ease of use. The part I was mostconcerned about failing, the ignition module, isinexpensive and easily available at any auto partsstore. I decided to go back to the original distributorand module/coil.

After re- tting the Delco electronic ignition, itran well for several years, then it began to getprogressively harder to start. Finally it requiredliberal use of starting uid and lots of cranking toget the car to re. Once it was running, it wouldhave a terrible miss for some seconds then theother cylinders would start to re. Then it would runnicely and smoothly with no problems until the nexttime it had not been run in 24 hours. Ultimately, thecar would not start at all. When that happened, Ichecked all the electrical connections and they allseemed to be clean and tight. I then tool the coilwire off the distributor and attached a spark testerto the coil wire. When the engine was cranked, nospark was present. No spark was present, evenwith a tiny gap to jump. Darn! I concluded that thecoil must be bad because the module had beenreplaced just a few months prior in attempts tocure the hard starting. The new module seemedto help the hard staring marginally, but it was stillridiculously hard to start.

Assuming that the electrical connections and thenew module were not the culprits, I concluded thatthe original 32 year old epoxy coil was no longer



functional. I started the hunt for the mythical TR7HEI coil. For along time before this I had beenkeeping my eyes open at places like Ebay for aNOS TR7 coil, and I never saw one. I had readsomewhere that the same Delco-France module/coil unit had been used by Peugeot. I thensearched for a coil listed as be ing compatible withthe Peugeot 504, or 604 from the early 80’s. OnEbay I found someone selling two coils for thePeugeot 604. In the photos, it these looked tobe very similar to the TR7 coil, except that theyhad a male “HEI style” high tension wire terminal(it looks like the terminal of a sparkplug). I boughtone of them and found that it was a perfect t inthe original mounting holes on the cast aluminumframe. I also found a GM D525 coil that also lookedvery promising. The epoxy coil itself looked a littlelarger than the TR7 or Peugeot coils, but the frame

looked about right, so I ordered one of them. TheDelco D525 is easily and inexpensively availableat car parts places like NAPA, and the quality istypically quite good. When I got the D525, I foundthat it DID t the frame, but it uses the alternate setof holes that were already drilled in the frame. I justhad to tap them for 4mm x 0.7 metric threads. TheDelco electrical part of the coil was bigger thanthe TR7 and Peu geot coil, so I guessed it mightput out more spark energy. I decided to learn howto measure the parameters of coils to determine

which ones are more “power ful” than others. Referto Appendix NN for information on how to measurethe coil electrical parameters and what they meanfor spark power.

When I left off, my car was not starting, andappeared not to have any spark. Since the modulewas quite new, I had concluded that the coil wasnot working properly, and was not able to deliver agood spark. I searched for a replace ment coil, andsettled on the D525 as a coil which ought to delivera good spark at cranking speeds. Unfortunately,when I reinstalled the upgraded ignition there wasstill no spark! As I was testing coils, I had founda schematic for a transistor interface betweenpoints coil and an HEI module. I put that interfaceon the electronic ignition as it sat on the car and

manually triggered the ignition module with apoints distributor. I got a good spark. This mademe conclude that the problem had to o with thedistributor. I checked the re sistance of the reluctorpickup in the distributor and I got about 800 ohmswhich is apparently a good number, so thereappeared to be no break in a wire. There was nocontinuity between the reluctor and ground, so itwas not shorted out. I did see some sort of ACsignal coming from the reluctor, but I had no datato indicate what sort of voltage to expect, nor whatvoltage is required to trigger the ignition module. Isuspected that my pickup was putting out a voltageat the very edge of enough to trigger the module.Maybe the magnet in the reluctor was weak.

I needed to get another distributor for comparison. As luck would have it, a Delco elec tronic distributor

had recently been on Ebay, and had not sold.I contacted the seller and bought it. As soon asit arrived I tried it on my electronic ignition. I didnot need to install the distributor. I could hold thedistributor and turn the rotor man ually. As I did so,I succeeded in getting spark from the coil! I couldtrigger the coil down to one revolution every 4seconds. I think cranking speed is faster than that.Unfortunately, the Ebay distributor was in roughshape. I could not drop the distributor in place ofmy own unit. I would have to dismantle the new

distributor and transfer the pickup to my distributor.

Before I did that, I looked for a new or NOS reluctorpickup. Thre are hundreds of vari ations on a themeavailable. I found two likely looking 4-cylinderreluctor pickups and ordered them. They were lessthan $20 each including shipment. Unfortunately,neither looked like a good match, an I did notanticipate being able to drop the pickup into mydistributor directy. But maybe the magnetic sensorcoil in one of the new ones would be a match forthe original in my car. And maybe the magneticpole piece would be interchangeable.







Appendix AAA

Why HEI is a Good SystemWhere does the “High Energy” of a High EnergyIgnition come from? Ignition designers always knewthat they could get more spark energy if they couldhave more current in the coil. They could achieve

this by having more current. Energy is proportionalto the square of the current. Unfortunately pointscan handle only up to about 4 amps before thelifetime of the points is seriously degraded dueto arcing at the moment the points open. Onceelectronic switching was robust enough to survivethe induced voltages from switching a coil,automotive designers didwhat they always wantedto do: Get more currentthrough the coil. But it is notquite as simple as that. Ittakes time to get the energyinto the coil. Chargingtime is proportionalto the coil inductancedivided by the resistance.Lower resistance allowsa greater current, but alarge inductance slowsdown the ability to build up

that current. An inductorhas magnetic “inertia”which only allows current to build slowly. At highRPMs there is less time to charge the coil, so ahigh inductance coil will not have enough timeto fully charge. So, designers needed to lowerthe inductance to a degree, depending on theapplication. For a high revving V8, they needed alow inductance coil to get full energy at high RPMs.Unfortunately, spark energy is directly proportionalto inductance, so to keep spark energy constant,

current would need to be increased a little as theinductance drops. This issue was later addressedby using multiple coils, eventually one per cylinder,as found on many performance engines today. Inthe 1970’s, they used one coil, with a low enoughinductance to allow adequate charging over thefull RPM range used by a particular application.Our 4-cylinder engines can still use a fairly highinductance coil without much of a tradeoff at highRPM.

Another factor that the HEI designers addressedwas heat. If you charge a coil longer thannecessary, then you are turning all that current into

heat. You only need to start charging the coil at atime dependent on the RPM. You want the coil tohave JUST reached full current at the moment thenext spark needs to be created. The HEI ignitionmodule has a current limining circuit so no morethan a safe current is provided to the coil. Butbefore that current limit is reached the module has

minimal resistance to current ow, and thereforeproduces minimal heat. In current limiting mode,there is a lot of heat being generated by the ignitionmodule. But the module measures the time ittakes to reach the current limit and starts to charge

the coil just early enough to barely hit the currentlimit. Current is limited by the coil resistance andinductance, not the ignition module most of thetime. Therefore, there s very little heat productionby the module, and as little heat production inthe coil as possible. Just a few watts in the coil,compared to the 70 watts that 3 ohm coil mightproduce with points!So, the HEI designers were able to achieve highspark energy while having a more ef cient ignition

Figure 1. Tis shows the relative spark energy vs RPM of the HEIcoils which t the R7 electronic ignition frame. Te Points curveis for a standard 12 volt coil and 60 degrees of dwell, not the VERYshort 39 degree dwell specied for the R7.



system and less waste heat. But how much betteris it really?

Figure 1 shows the relative spark energies vs. RPMof the several coils listed in Chart 1 in AppendixCCC. A 12 volt (3 ohm) coil with points is shown forcomparison. You can see that the low inductancecoils tend to maintain a more constant sparkenergy over the RPM range. This is because theyhave time to fully saturate the magnetic eld. Highinductance coils have do not allow the coil currentto climb as quickly, and at high RPM they do notget as much current by the time the spark needsto re. The data used to create these graphs wasbased on a mathematical model of the coil andsparkplug. The current was limited to 5.5A, anddwell was adjusted to allow the coil to just have

time to reach the current limit before the next sparkevent. This is the same way the HEI ignition moduleworks. The 3 ohm coil does not use any externalcurrent limiter, its inductance and resistance limitthe current to a safe value for points. The dwellwas set to a xed 60 degrees as used in te TR2-4a4-cylinder engines. This dwell value is considerablylonger than the recommended 39 degrees for theUK points-equipped TR7, but it allows much bettercoil saturation. It is not clear to me why Triumphrecommended 39 degrees of dwell for the TR7.

Some other points-equipped cars ( e.g. VW) use adwell of about 52 degrees.

The Delco D525 coil has a higher inductance thanthe TR7 or Peugeot coils, andas a result has a much higherspark energy. But it has troublemaintaining that energy all theway to red line. The originalTR7 coil has a comparativelypoor spark energy, but itappears to be intended to bean HEI version of the 3 ohmcoil, with improved high RPMperformance. The Peugeot coilis about midway between theD525 and the TR7 HEI coils.

Six cylinder engines have 50%more spark events for the sameRPM compared to a 4 cylinder. And 8 cylinder

Figure 2. Relative spark energy of various coils. Te pointscurves are for a 12 volt, 3 ohm coil with 60 or 39 degrees of dwell.

engines have double the number of spark events.So, the 7000 RPM point in Figure 1 would be 4666RPM on a 6 cylinder and 3500 RPM on an eight.The D525 coil’s output is dropping quickly at 7000RPM (on a 4-cylinder), and on a 6 or 8 cylindercar, the spark energy may not be adequate athigh RPM. The graph suggests that the D525 coilmay be intended for 4 cylinder engines, and thePeugeot coil, with its very at graph, may havebeen intended for a 6 cylinder engine. It appearsthat both the D525 and Peugeot coils are superiorto the original TR7 coil for a 4-cylinder engine.I chose to use the Delco D525 on my upgradedignition system.

Other TR7 Ignition SystemsThe TR7 initially used the Lucas Opus electronic

ignition in the US, and it was always suppliedwith a points system in the UK. The Opus systemhad an extremely high failure rate, and many ormost of the original Opus systems have beenreplaced. Triumph dealers were using the LucasCEI (Constant Energy Ignition) systems as thereplacement for the Opus. The Lucas CEI usesa variable reluctor pickup similar to the US Delcodistributor, and its ignition module was simply astandard 4-pin HEI module in an enclosure. I amnot sure what coil was used with the CEI system,but it was not a typical HEI “E-Core” coil. It wassome sort of cylindrical coil. I strongly suspectit was a standard 1.5 ohm coil with no ballastresistance. Figure 2 shows the relative spark





With the help of the TR7-TR8 forum, I was able toobtain the data on the various Delco distributors ttedto the TR7. The tables are included at the end of thisarticle. A graph of the centrifugal advance curves isshown in Figure 1 here. I was surprised by the wide

variety of curves that were used. I would have thoughtthat for a speci c state of tune (mostly determined bythe cam and compression), the advance curves wouldhave been very similar. The “early” UK points typedistributor was used with a high compression engine

and with vacuum advance. I might have thought thatthis would have the most gentle advance curve, andit does. But the “late” UK distributor has the mostaggressive curve, and it also uses vacuum advance!Is the lower compression that signi cant a factor indetermining the best advance curve? I don’t know. I doknow that one can use a seat of the pants technique todetermine the “optimal” advance curve. In general, youwant as much advance as you can get without causing

pinking, not even a little pinging. This is hard to dowith vacuum advance-equipped distributors because

the total advance depends on the manifold vacuumwhich is RPM, throttle, and load dependent.

Given that the “UK-Late” curve is used on a lowcompression engine like the US engines, it would appearto be safe to use a UK-type vacuum advance moduleon a US distributor originally equipped with a vacuumretard unit. The advantage of this is that the enginereally needs more advance in partial throttle cruisingsituations in order to get the best performance and fuel

economy. It might make a few MPG difference.

Advance Measurements

Unfortunately I do not have a “distributor machine”

which spins a distributor and can measure the advanceacross the RPM range. All I can do is photograph therotation of the advance mechanism with no advance andmaximum advance. By superimposing the two images,I can measure the degrees of rotation of the advance

mechanism.

I measured the amount of centrifugal advancefor the UK distributor. This unit does not useany limit bushings to control the advance.The window alone controls the maximum.

The measurements showed that it had 9.75degrees of distributor advance (19.5 degreesat the crank).

When I stripped a US Delco distributor, I wasrather surprised to nd perished bushings onthe centrifugal advance limiter pins. TheUK distributor does not use bushings andthe window is just large enough to allow fullcentrifugal advance. Older American non-

HEI Delco distributors did use a limiter bushing, but notthe HEI distributors. The shape of the top plate, and thestrength of the springs determine the maximum advanceand bushings are not needed for US HEI distributors.This distributor looks to have been rebuilt or recurvedat some time. I can’t tell if the bushings were originalto the distributor or a later addition. When I lookedat my own distributor, I found that it did not have any

bushings, and there were no apparent persihed remainsinside the distributor. So, it is unclear to me whether

bushings were tted originally.

On a US TR7 Delco distributor without any bushing,I measured 15.14 degrees of maximum distributoradvance (30.28 degrees at the crank). If the distributorcan actually reach this amount of advance with theoriginal weights, top plate, and springs, then this 30degrees of advance in combination with the 10 degreesof basic advance probably adds up to too much advanceat WOT. I had on hand a new HEI pivot bushing which

ts the advance limit pin. This bushing had a thickness

Appendix BBBADVANCE CURVES



of about 0.031” and an ID of about 0.190” and an ODof about 0.252”. A length of no more than 0.300 wouldallow an E-clip to lock it in place. When measured,it did little to limit the advance, giving 14.73 degreesat the distributor. A thicker limit bushing seems to beneeded.

I retrieved the perished remnant of the original bushingas tted to the distributor. This had a thickness of 0.050”to 0.060” and a length of 0.268” Assuming a 0.190inner diameter, then the outer diameter would be about0.300”. When I used it for the advance measurements,I got 10.74 distributor degrees (21.48 crank degrees).This is in the correct ball park, and probably I was

pushing the advance harder than the centrifugal weightsdo, causing a little extra advance. McMaster-Carr hasTe on tubing (8547K24) available in 1 foot quantities ata reasonable cost. The OD is 5/16 (0.3125) and the ID

is 3/16 (0.1875) with a wall thickness of 0.0625”. I havenot tested this tubing for its performance, but it is theclosest I have found so far.

As I said, it is not clear to me that a bushing is required.If you get pinging at WOT, and have to retard the sparkmore than a small amount, then maybe you do needto add a limit bushing to your distributor. Testing thedistributor on a distributor machine would tell you thewhole story. Jeff at Advanced Distributors said he canservice these units and you can tell him the curve you

want, and he can tune the distributor to that speci cation.I suspect that something like this had been done to mytest distributor.



Appendix CCCCalculating coil electrical parameters

Coil Electromagnetic Speci cationsR Primary R Secondary Turns L Primary L Secondary

Original TR7 0.6 ohms 10.0K ohms 106:1 4.06 mH 45.79 H

Peugeot 5048 0.6 ohms 5.0K ohms 75:1 5.60 mH 31.5 H

Delco D525 0.6 ohms 8.25K ohms 100:1 9.46 mH 94.6 H

Chart 1. Tis shows the parameters of the HEI coils that I found which t the R7 electronicignition coil mounting frame. Tere is considerable variation between coils which are physi-cally fairly similar in appearance.

It is easy to get a fairly accurate measurement of theelcctrical parameters of an ignition coil. It is essential-ly a transformer. By measureing the inductance of theprimary windings, you can calculate the inductance ofthe secondary windings if you know the turns ratio ofprimary to secondary. ypically the turns ratio is any-where between 75 and 110 to 1. It is a little harder tomeasure the resistance of the primary when it is under1 ohn, as the HEI style coils are. But a regular digital volt/ohm meter will suffice.

o determine the coil inductance, you create a tunedcircuit by placing a 0.1uF ceramic capacitor in parallelacross the primary coil terminals. Ten you feed a variable frequency sine wave through a 1000 ohm re-

sistor, thru the parallelled coil and capacitor to ground.You measur ethe voltage across the coil terminals asyou vary the frequency of the supply. You will see the voltage peak somewhere around 2000 Hz. Ten usethe formula: L = 1/(2 * Pi * F * root(C))^2. Tis givesyou the overall inductance of the primary windings.

o get a complete model of the coil, you also need tomeasure the inefficiency of the magnetic connectionbetween the primary and secondary coils. Standard cy-lindrical coils are a little less efficient that “E-core” coilsbecause the E-core coil has a closed magnetic loopwhich recuded losses. Some of the inductance of theprimary windings does not contribute to induced volt-age in the secondary windings. Tis is measured the

same way as the total inductance, but it is done withthe secondary hot lead shorted to the positive primary

terminal. Te peak voltage will be somewhere around4KHz to 10Khz, Tis inductance s called the “leakage”inductance. Tis is subtracted from the total prima-ry inductance to determine the amount of primaryinductance which does induce voltage in the secondary

Figure CCC-1. Schematic of the tuned circuit to measure the coilinductance

Figure CCC-2. Measuring the turns ratio of the coil



windings. Te secondary winding inductance cambe calculated by multiplying the primary inductancesby the quare of the turns ratio. For a 100:1 ratio, youwould multiply the primary inductance by 10,000 toget the secondary inductance.

Te turns ratio is measured by feeding a sine wve intothe secondary windings and then measure the stepped-down voltage across the primary terminals. Te ratioof the voltage is equivalent to the ratio of the turnsbetween the primary and secondary windings.

Tese topics are discussed in-depth and very clearly byHugo Holden in his article : http://www.worldphaco.net/uploads/ELEC RONIC_IGNI ION_FOR_ R_CARS.pdf. His website at http://www.worldphaco.net is an excellent resource for many electronic issuespertaining to Rs.



Appendix DDDPart Interchange Information

PAR IN ERCHANGECoil Peugeot-type: Original Engine Management #5048 (reuses original wiring harness)

Delco D525 (NAPA MPE IC22SB) (needs new wires to module and car)Ignition Module Delco D1906 (stock type module and very reliable)NAPA ECH P45 (probably same manufacturer as the D1906)Pertronix D2000 (street: about 5.5 amp current limit)Pertronix D2070 (Race: 7.2 amp current limit)

Variable Reluctor pickup No exact replacement: reuse original back shell.Wells DR-102, NAPA MP102, Delco D1910, LX311(Star ring is very close match(or perfect), the pickup coil wires are correct).Wells DR-107, NAPA MP107, Delco D1966, LX310 (star ring stator is a perfectmatch, the pickup coil wires are reversed).Te permanent magnet is correct on both the DR-107 and DR-103. (Probably anypickup module magnet with a similar size/shape will work regardless of the cong-uration of the star ring stator).You will probably need to cut off the small indexing tab on the pickup coil to beable to orientate it properly in the shell (the original coil had no tab).Te pickup coil Green wire always goes to the “G” terminal of the ignition moduleregardless of which side of the pickup it comes off.













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Delco Electronic Ignition