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I have 2 ad's one 49 and 1 51 5 window. Both engines are rebuilt 1954 235 one has Rochester B carb, one has 32/36 carb from Tom Langdon. What are the advantages/Drawbacks of electronic Ignitions? If I got them I would go with Tom Langdon_thanks Bill

Not too many drawbacks. The 235 will run fine with a points dist but the HEI system avoids points and allows you to use a wider gap on the plugs (better spark, etc). I've used both and prefer the HEI.

Langdon's distributor is fine and of course Tom is also. I'm using one now. Avoid the Chinese stuff.

One needs a 8 size wire to feed a HEI, so beware of that, good place or a relay. Any late Chevy or GMC 6 cyl that is not odd fire will work.

Ed

Agree with Jon. Buy a Langdon. But points are just fine.

Ed, what are you saying? 8 ga...where? Never heard that before.

8 ga might be overkill, but I suppose too much isn't necessarily a bad thing. 10 ga run through a 30/40 amp Bosch style relay is fine. The coil on some of these has an initial startup load of between 20 and 30 amps to energize and this will cause ignition switches to burn out...in fact I have one sitting in the garage that lasted for about 6 starts before it fried. You're safer using a relay and please be certain to check the size of wire going in and out of the relay. Some of those relay harnesses come to you wired with 16 ga wire and that won't be sufficient for anything but the relay's coil in this case. Pin 85 is ground for the relay's coil, pin 86 is to ignition switch (+ 12v) to activate the relay's coil, pin 30 is to 12v positive (from battery--needs to be 10 ga) and pin 87 goes out to HEI coil--also 10 ga. There may be a pin 87a in your harness but ignore this. It is for normally closed and you must wire through normally open for the relay to work correctly. You need to remove the connector clips from the harness and change to 10 ga. The replacement ignition switch I got was rated for 30 amps, but I'm going to give it some breathing room with a relay. Once the engine is running, the HEI takes much less amperage...maybe between 3 and 4.

No relay. 12ga wire. Where is all this crazy stuff coming from? It's just an HEI. There is no stress on the ignition switch and no need for big wire. Are you guys confusing an HEI with a new starter?

You are correct. A pink 12 ga wire is shown on the wiring diagram I have. I acquired the official wiring diagram from GM when I bought my 1980 C20.

Crazy, eh? Interesting comment. I'm sitting here with a fried ignition switch that was made long before 1980 and only rated for 15 amps. I'll bet there are quite a few of them still out there. A 12 ga wire might be suitable. I'd prefer the margin of 10 ga, however. But rest assured the 15 amp ignition switch was the weakest link in this circuit, I didn't feel smart for overlooking something this basic, a relay would have meant that switch would still be ok and it failed because of the extra load. The amperage rating of that switch wasn't put there as a suggestion. So let's not be telling anyone here an overload on their ignition switch won't make any difference. That's not correct and it isn't prudent. Exceeding the amperage rating of any switch can cause premature failure and could even cause a fire since there is no fuse protection.

The GM HEI coil is current limited to 5.5 A. The duration of the load is 3 milliseconds average. The ACCEL and others are 7.5 A current limited. I don't doubt that your switch failed. If you are sure it was not the starter, please advise how a relay is wired to protect an ignition switch from an HEI.
Is the idea to turn on the ignition, which turns on the relay, which turns on the HEI?

I'm certain it wasn't the starter. The starter and that ignition switch have been peacefully coexisting for 40 years. It got new brushes and bushings but not within the past 8 years.

The HEI is current limited but not when it is energizing. When you first kick it on, it is flooded by 20 amps or more. In a bit I'll tell you why. There are questions and discussions like this on other forums (example found in about 3 seconds on Google):
https://www.chevytalk.org/fusionbb/showtopic.php?tid/188589/

or even here at our forum:
https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=408413&page=2

And like any other subject you search for on the internet, you'll run across plenty of hooey.

If you want to run a relay (which I believe isn't a bad idea given you may have one of the old ignition switches) then run a wire from the "ign" post of the switch (will be 12 v positive) to one side of the relay coil and ground the other side. The pins on the relay will be 85 and 86. I believe most people use pin 85 for the ground pin. Then run a number 10 or 12 ga wire straight from the battery (most will advise against tying in at the starter where the cable connects but some people out there may have other thoughts on that) to pin 30 (I think I mis-typed that earlier) and then run another length of 10 or 12 ga wire from pin 87 (the normally open one) on the relay to the HEI coil connector. Your relay harness may have a wire connected to pin 87a. You can and should remove this as it is normally closed and will feed 12v through that wire to any convenient ground when the ignition is off. Wired correctly, when the coil energizes you'll get a large and healthy shot of electrons right straight in to it and it will be instantly ready. As long as the ignition is on, your HEI coil and distributor will be happy. These relays and harnesses are cheap, by the way. I bought a box of 5 on Amazon for less than $10 a year or so ago.

Now let's think about this whole HEI wiring scheme for just a bit. You say the HEI coil is limited to 5.5A. Yet when they began using the HEI, GM started using a pink 12 ga wire going to the coil. If the ampere needs of the GM HEI coil will be less than 6 amps and the wire isn't longer than 7 feet, it is generally accepted that 16 gauge wire is fine (up to 10 amps and this gives a cushion of nearly 50%). Why would GM spend the money on higher rated ignition switches and 12 ga wire? They wouldn't have without a good reason. If it would have worked, they would have made sure the harness wire to the coil was 7 feet or less and wired it with 16 ga wire and continued to use wimpy ignition switches and relays for things like A/C, cooling fans, horns, lights and any other high amp needs. But you won't find any instructions out there telling you to try to run your HEI on 16 gauge wire because of one fundamental flaw. Wire that size will energize the coil but it is going to take a while. And the whole idea is to make the engine start quickly. If the engine takes a long time to start, people start taking cars back to the dealership for service. And without a fully energized coil, quick starts won't happen.

Just a couple of points, straight from the GM training center course I took back when HEI was a brand new system- - - - -The current limiter doesn't kick in until the distributor module sees 100 distributor RPM (200 at the crankshaft) and it has to function EVERY time the coil conducts- - - - -60+ times per second at cruise RPM. Also- - - -aftermarket clones of the HEI module, even supposedly high quality ones, DO NOT have current limiting circuitry included. I've proved that repeatedly while watching oscilloscope primary wave patterns.
Jerry

Hello! No "finger pointing here". Just looking for some perspective.
As I read this, it occurs to me (as previously having been an electrician); that if 14ga (single strand) wire is
perfectly adequate for a 25 amp circuit. How is it not adequate for a lesser amp ignition circuit? I know
for a fact that I can easily run 30 amps on that same circuit and still have a "cold" wire. The gauge wire
on all the headlights, blower motor, and horns I've ever seen have never been more than 12ga, and most;
especially now-days are 14ga. The old blowers, and especially the horns (as they aged) could really
draw down some amps. Probably tickling that 30amp breaker/fuse. But I really struggle with the HEI
ignition having anymore that some 2.25amp load. Is it not possible that given that the ignition switch was
as old as it was that the contacts were worn, or loose enough to the point there was not enough contact?
Effectively making the contacts less than 14ga, or even less? That could easily cause the switch to burn
up. Not trying to be at all argumentative. Just trying to make it all make sense in *my* mind.

Appreciate your indulgence!

--Chris

Let's do some simple Ohm's Law calculations- - - - -the average HEI coil primary winding has about 1/2 Ohm of resistance. With an alternator operating voltage of 14.7, that gives a surge current of almost 30 amps before the inductive reactance of the coil winding and the current limiter kicks in. This happens every time the winding conducts, three times per crankshaft revolution for a 6 cylinder, or four times for a V8. That's pretty close to a constant 30 amp current flow in practical terms. I can see where a tired 50-something year old ignition switch might have problems, and an overseas-made aftermarket knockoff won't be much better. It makes sense to me to engage in a little overkill and use a 60-amp Bosch type relay and 10 gauge wire to carry the main coil current, and turn it on and off with a couple of amps from the ignition switch through the relay coil circuit. "Your mileage may vary!"
Jerry

Hi Chris,
Maybe it would be ok to think of the coil as a 5 gallon bucket which needs to be filled up as quickly as possible. And you have two means: one is a fire hose and one is a garden hose. Obviously the fire hose is the one to use. Unlike a capacitor which also holds a charge until needed, the coil increases voltage and without that coil (or any coil for that matter) being charged fully the ignition system won't work. And as Jerry correctly pointed out it must be charged repeatedly with each conduction cycle. But...it doesn't have to be charged fully with each cycle. And that's why it takes less amperage when the engine is running. It is sort of like a swamp cooler that uses a float to fill the reservoir when evaporation depletes it.

My idea of using 10 ga wire was that it would be like a larger fire hose. More comfort in my mind that the coil would be charged very quickly when the key was turned on. And GM knew that had to happen or 12 ga wire wouldn't have been used.

As for the sizes of wires, here's part of a guide I found and saved which may be helpful (I won't go all the way down to 2 gauge but will start at 10 gauge):
10 gauge for as much as 150 to 200 amps at 3 feet or less, 100 amps for runs of 7 to 10 feet, 30 to 50 amps at runs of 15 to 20 feet and 20 amps at runs of 25 feet.
12 gauge for as much as 100 amps at runs of 3 to 5 feet, 75 amps at 5 to 7 feet, 50 amps at 7 to 10 feet, 40 amps at 10 to 15 feet, 20 to 24 amps at 15 to 20 feet and 15 to 18 amps at runs of 20 to 25 feet.
14 gauge for 50 amps at 5 to 6 feet, 40 amps at runs up to 7 feet, 30 amps at up to 10 feet, 15 to 18 amps at 15 to 20 feet and 11 to 12 amps at runs to 25 feet.
16 gauge for 50 amps at up to 3 feet, 30 to 40 amps up to 5 feet, 18 to 30 amps at 7 to 10 feet runs, 8 to 12 amps at 15 to 20 feet and 8 to 10 amps at runs up to 25 feet.

So, 14 and 16 gauge wire sizes allow for lots of different uses and as you can see can handle decent amounts of amperage.

Was the ignition switch worn out? I can't say...I haven't taken it apart yet but I saved it out of curiosity. It was 40 years old, but I should add it had not been used every day or even every week for 40 years and there was a period of over 15 years where it sat in the garage and wasn't used at all. So I'll be surprised if when I take it apart I find abnormal wear. But would wear to the contact points or loose contact points have reduced their amperage ability? I would say it is reasonable to think that, but it is hard to say (or know at this point) how much. It was however a good switch, made in the USA, heavy case, heavy bakelite back and all that. Hopefully this is helpful.

Gentlemen, this is not an issue to get cranked up about. I have a different opinion and am trying to reason it out. Knowing that I have NEVER heard anyone blow a switch with an HEI swap, including myself. Some folks are scrambling the issue and bouncing around.

1. My initial comment was that 8 ga was advised, "crazy stuff" was made in that context...... and where was this stuff coming from? You are not crazy and your wish to be prudent is not. I just want to give all those who read your comments a second opinion.
2. I said 12 ga...... Everyone now is saying 12ga like I said 16ga or something. You have come down to 10 or 12 ga. Good for you. Now you are asking me why GM would spend the money for 12ga if it was not need. I am the guy that first said 12ga. Double talk is a bad way to discuss.
3. You found some stuff on Google. I had already read that yesterday, as well as "And like any other subject you search for on the internet, you'll run across plenty of hooey." as you stated. I also read some other hooey http://cyberdave.org/HEICoilInfo.html
4. Let's don't have a "my hooey is bigger than your hooey"
5. I advise to just use 12ga and no relay, you can advise other. You guys can explain electricity to someone else. Quote the Bible if you want.
6. I read several "googled" info yesterday. I read many things, dozens, and try to use info from what seems to come from good sources. This one is an article and has sources listed at the end http://www.superchevy.com/how-to/67498-hei-coils-modules/
One of my links is from a person doing a study, with charts, and took the time to list all sources. The other is from a well known magazine with writers who do their homework and listed their sources.
Please read that GM is about 5.5 A and that aftermarket "super spark" HEI's are limited. (about 7.5A) They have simply allowed more amps so as to say they have better "spark energy". Ad hype like: "cleaner whiter clothes" or "your hair will have more body". Anyway just read the full article in Super Chevy. The other one is too long and boring. I provide these just to show that I do try to check from all sources, including Jerry.
7. Your first link is just a bunch of bloggers like us, quoting other "guys" they heard say such and such. Your other link is a prolific member info source for Stovebolt members like us. Jerry has great knowledge. Readers here can take their pick of sources and look up their own stuff.

OK I stepped into this carefully *knowing* there are (like me) some grey beards with a lot of wrenching
under their belts, and the pride they earned accumulating all that hard wrenching.
That said; I fancy myself pretty d@^! handy with electricity. Worked with it almost all my life. I'll be
enjoying absolutely free electricity in the next couple years as a result of what I know, and I *won't* be
using any of the "technology" anyone uses to accumulate/obtain electricity. But I digress. Perhaps in
another thread/discussion.
I like the "bucket" analogy you used Jon. I often find myself using water to help others visualize
electricity. But I do it like this; AMPs = VOLUME (like your bucket). VOLTs = SPEED
Example; in auto speak... I can arc a plug with less than 10k volts, and just a few milliamps. But I can
(attempt) to apply 600 amps to that same plug at less than a volt, and there won't be enough volts (speed)
to cross the arc. In spite of the fact there are enough amps to kill a person. The same cannot be said for
volts. Ever been zapped by a coil or spark plug wire? 20-80k volts will sure startle a person. But anyone
in reasonable health will escape the experience unscathed.

The point I was trying to make, was it seemed more likely to me that (due to wear from age) there was not
likely enough surface area to accommodate the AMPs (volume) required. Or perhaps that, and some
accumulated corrosion on those contacts (corrosion = resistance = equals (additional) ohms). Unlike water, electrons
never stop moving which causes friction, which causes additional heat. Given an opportunity (passage) those
rated amps traveling at the speed of 12volts will (because the contact(s) are inadequate, build up heat.
Causing the ultimate failure I believe you experienced.

Your numbers are impressive, and I'll not argue them. I'm only speaking from my own experiences with these
things. I've run everything from dragsters with 392 dodge HEMI's to quater miler stock cars, to rally in a
Datsun 1600 roadster. I'm NOT claiming "expert" just having enough experience to engage in a lively discussion.
All the "stockish" GM HEI's I ever worked with, had no trouble(s) with a 14ga wire running to the bat side of the
"top coil". I knew that at curb idle that the charging system delivered some 2.5amps. Meaning; that I could
disconnect the positive cable while the engine was running, and it wouldn't die. I always assumed that they
rated the first gate at that amperage because it was guaranteed to satisfy the demands of an idling auto. Keeping
the battery from experiencing discharge.

@Jon
While my experiences draw a different conclusion than yours. That doesn't mean you won't ultimately prove me
wrong. While I'm not banking on it. I'm also never too old to learn something new.
IOW any rebuttal I engage in is NOT personal.

In fact, I have everything I need to put my theory/understanding to the test. I'll put everything together this
weekend, and perform some tests with the actual gear we're discussing, and come back with my findings.
h3ll, I may even make a video of it all. So no one can claim "bull".
OTOH I might well find everything you've said is gospel.
I'll be back to this thread with my results this weekend.

All the best to you!

--Chris

The old ignition switches were built for 6V. They are one of the largest switches on the truck if not the largest. Built large with large contacts. If it was an original switch, it was "worn out", pitted, corroded, loose, weak contact springs/strips and burnt from sparking 142,350 times. All this blogging about relays and 8ga and the theory of electricity is about an old switch that failed. All opinions, theories and experiences are respected.

Average old switch: 6 starts per day, 365 days per year for 65 years= 142,350. As Jerry says; Your mileage may vary.

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