On using GM HEI ignition modules

[wcorey]

This is mostly just an overview to what is already available from other sources, I’m certainly not big on re-inventing the wheel here…
It’s all basically a tried and true technology that has been adapted to countless applications over the years and I can’t imagine why it wouldn’t work for Ducati singles.

Found some very extensive info online for GM HEI modules adapted to motorcycle use. This http://home.comcast.net/~loudgpz/GPZweb/index.html#home is the most comprehensive site I’ve found with more info on this than I think anyone could need and lots of other interesting and useful stuff besides, be sure to bookmark it. The click-able sections for the HEI mod’s are right near the top. This guy is very thorough and meticulous.

I have a handful of modules left over from old Chevy 350 projects so I tried it out on the bench. Hooked it up to a Dyna coil and triggered by an XR125 pickup coil that's pulsed with a little high power refrigerator magnet embedded into an aluminum adaptor affixed over the stock points cam. You can also use points to trigger it and with an additional bypass circuit have the piece of mind of going back to stock point/condenser/coil with the flip of a switch. You can even add an LED to visually indicate the triggering point.
While the HEI’s will switch with points, one complication is that it triggers on closing rather than the normal opening but with still some more very simple circuitry this can be reversed. This really only needs to be done for the bypass to work as intended

For me this project started when I came across a box of 70’s Toyota Celica igniter boxes and pickups that I was putting on British twins and Harley’s back when. I guess the HEI route didn’t occur to me at the time and/or because I had a Celica and easy access to the Toyota parts for free. Can’t see the sense in resurrecting that old stuff now though as it’s probably now difficult to obtain spares, and it’s really Old. Might try the pickup's though...

I noticed that there are at least two basic types of pickup coils, one is a plain coil and requires a magnet to trigger, the other has the addition of it’s own magnet and only requires a simple rotating steel/iron protuberance to trigger it. The magnet trigger type can consist of either the actual magnet rotating or a magnet fixed opposite the pickup with a steel plate or ring rotating between the pickup and magnet with a gap for triggering. This style seems most common and likely what I’ll end up using, as it seems easier to tweek.
Of course there are also the optical and proximity sensor types. I like the idea of the magnetic units with this application as the HEI’s are already set up for it, they're very basic and doesn’t need additional external circuitry to function, though it seems like the optical method may yield better accuracy/resolution.



The pickup is mounted out by 180 simply because the wire routed better that way and the magnet on the advance was a tight squeeze when on the high side of the cam lobe so I put it on the opposite side and don’t flip the advance 180 to compensate.



Magnet type pickup coil...




Bill

[Jordan]

Cheap solutions to keeping our bikes running well are always interesting.
I've noticed on my singles, that electronic ignition makes for easier starting.
Some questions on this GM HEI setup:
- I take it that the cars this module was made for has a mechanical advance-retard unit?
- Does the inductive pickup have an effect of varying the timing with engine speed? If the mechanical adv-ret were disabled, would the timing remain static?
- Is the timing sensitive to the polarity of the pickup? That is, do you get different timings if you change the pickup connections over?

As the factory electronic ignition systems fitted to Ducati singles achieve an adv-ret action without the use of a mechanical system, I wonder if this module would also work this way.

Jordan

[DewCatTea-Bob]

____ I've been holding-back my response to this very interesting thread because I have just too much to add and wonderings of my own concerning this area of ign.systems.
__ Jordan has brought-up some of the exact same wonderings that I've had, ever-since the 1973 350-Road model came-out with such a system of it's own !
While I never did become an expert on exactly how the electronics of these systems work, I have had thoughts about them which I've accepted as probable (but not concluded as actual fact),, so with that, I'll offer my food for thought on some of these questions...


" Does the inductive pickup have an effect of varying the timing with engine speed? "

____ The answer to that can certainly be yes, but with electronics, it's possible to do almost anything ya can conceive,, so in the end, it depends on the circuitry etc., of the pick-up.
__ Since the pick-up has to have a sensor -(no doubt a coil) that's sensitive to the magnetic-flux of the chosen trigger-magnet, and that magnet (of the rotor-trigger) has a steady/locked-in field of magnetic-flux lines which are spread-out weaker & weaker as the sensor is spaced further & further from the magnet,, and since the sensor is set (by it's particular circuitry & placement) to become triggered by a particular/certain amount of flux-field 'cutting' strength, and since cutting-strength increases as RPMs increase,,
then at lowest-RPM, only the magnet's strongest (center flux-lines) field is capable & required in order to be able to trigger the pick-up, however while climbing to higher-RPMs, the higher rate (thus increasing strength) of flux-field cutting allows the weaker (outer flux-lines) area of the magnet's field to produce sufficient cutting-strength to cause the sensor to develop enough voltage to trigger it's pick-up circuitry, sooner & sooner (as revs climb-upward, in the magnet's rotation-route).


" If the mechanical adv-ret were disabled, would the timing remain static? "

____ I'm sure that that would depend on the chosen electronics of the pick-up circuity and the physics of the particular magnet & sensor, such as their chosen minimum separation clearance.


" Is the timing sensitive to the polarity of the pickup? "

____ Likely not, (but if doing such could serve any useful purpose, then it could no-doubt be set up to make a difference, one way or the other).
__ Nor should the polarity of the trigger-magnet make any difference.
__ In either case, the static-timing & the advance-curve should stay the same (since there's probably never been any reason to make these differences cause any changes).
____ However I'd think that the exact ign.timing & advance-range/span would be sensitive to the particular space-clearance between the rotor/trigger-magnet & pick-up sensor...
So by altering that distance, I'd suspect that ya could alter the overall-span of the adv.range.


" That is, do you get different timings if you change the pickup connections over? "

____ That's certainly fairlly doubtful, but it's more likely that the circuit will only work properly when connected (polarity-wise) as intended.


" As the factory electronic ignition systems fitted to Ducati singles achieve an adv-ret action without the use of a mechanical system, I wonder if this module would also work this way. "

____ The HEI-module seems very versatile and so the answer to that no-doubt depends on the chosen pick-up/control-circuit type & it's particular manor of detecting & making use of the effect from the trigger.
__ The pick-up's coil-sensor may be triggered by either a SPINNING/dynamic magnet set-up, or, a STATIONARY/static magnet set-up, (where a piece of rotating non-magnetized [hopefully un-magnetizable] magnetic-steel transfers some magnetic-field (disturbance) from the stationary magnet to excite the pick-up's coil-sensor, which is mounted next to the magnet), so as to prevent any unintentional pre-triggering, (as is a possible effect from a 'rotating' magnet). _ This later/stationary type of set-up would (likely, to my thinking) work properly with a mechanical-advance method, for auto-ign.advancement.


____ I realize that my reply-post here is of very little help with these concerns but, some sort of a reply-post is better than no response-post at all, (I think),, and my main intent with this post is to inspire more of such related thoughts.


Hopeful-Cheers,
-Bob

[Jordan]

An inductive pickup, in itself, has no electronics about it - just a magnet and a coil in essence. I wondered if the waveform is "conditioned" further within the ignition module, but have not seen anything to verify that, and am now of the opinion that the adv-ret is a "dumb" system, at least on the simple CDI's used on Ducatis etc. The ability to vary timing with engine speed is inherent to an inductive pickup system - a happy situation. Tuning to get the required advance range can be done by changing the gap, using different strength magnets or coil turns, shaping the poles of reluctors - so who needs stinking semiconductors?
The electronics within the ignition unit respond to the pickup waveform to determine the firing point.
The reason I asked about polarity of the pickup, is that waveforms are often not symmetrical. See this graph from an aftermarket car ignition kit, which shows what's going on. The remarks on it are to ensure wires are connected in such a way as to NOT change with engine speed. I don't know how the waveform gets this assymetrical shape, but it'd evidently important if a virtually static ignition point is wanted. I don't think all pickups necessarily give an assymetrical waveform.

Jordan

Jordan

[DewCatTea-Bob]

" An inductive pickup, in itself, has no electronics about it - just a magnet and a coil in essence. "

____ First, lets keep in mind that a "pick-up" unit can just be merely a housed 'sensor' (or coil as you suppose), or, it could also provide other steps including that of an entire control-module with all the related electronics which allows the pick-up's sensor-coil's very small electrical-current signal to control that which fires the ign.coil.


" I wondered if the waveform is "conditioned" further within the ignition module,
.....
so who needs stinking semiconductors? "

____ I'm sure you have to already understand that a little pick-up coil can't by itself cause an ign.coil to make it's spark (like contact-points do),, and so the components of the related control-module have to be 'electronic' in nature with at least one semiconductor, which can't help but "condition" the circuit-current in some manor (desired on not).


" The reason I asked about polarity of the pickup, is that waveforms are often not symmetrical. "

____ I can't think of any case where that's true without semiconductors (or inductor-circuits) being involved. _ So the polarity of any particular 'pick-up' may (or may not) matter but, I don't see how the waveform of a simple coil-sensor might be much other than a varying symmetrical sine-wave.


" See this graph from an aftermarket car ignition kit, which shows what's going on.
I don't know how the waveform gets this assymetrical shape, "

____ I'm currently at a loss to explain exactly what that graph is actually intending to show the results of. _ Those non-matching climb & fall rates are more likely the results of more circuitry than just that of a sensor-coil.

____ Otherwise I'm pretty-much FULLY on-board with your worded-thinking, Jordan.
__ Again, since I'm not an expert on any electronic-ignition triggering-systems, I haven't really meant to submit any good answers,, just mainly comments with hopes of spurring more interesting thoughts.


Fun-Cheers,
-Bob

[Jordan]

It's just the adv-ret function I was addressing, which I believe can be derived by design of the inductive pickup alone. Non inductive types - points, optical, Hall Effect and anything else that produces a square wave won't be able to do that, and then you need either to use a mechanical unit or go electronic, probably digital nowadays, to get the advance effect. Ducatis by the way have good quality mechanical bobweight system of adv-ret, so keeping it is not a bad option. I'd like to know more about assymetrical waveforms as I don't fully understand how they are made. Some ignition systems with inductive pickups use a sort of snail cam shaped reluctor, which would be an explanation, as they are not symmetrical too. But then some just have a simple regular pole piece, but I think still produce a non-symmetrical waveform?

Jordan

[wcorey]

Don't even know where to start here, I think there's been a little bit of a disconnect between the intent of the questions and answers given.

- I take it that the cars this module was made for has a mechanical advance-retard unit?

Correct. The 4 pin HEI's don't supply advance, though they do have a unique, efficient method of controlling current and dwell to the coil that's a big improvement over points. I believe the 5 pin ones have some limited form of advance (or retard actually) specific to a 'limp home mode', not applicable here.

- Does the inductive pickup have an effect of varying the timing with engine speed? If the mechanical adv-ret were disabled, would the timing remain static?
- Is the timing sensitive to the polarity of the pickup? That is, do you get different timings if you change the pickup connections over?

A lot of your questions are covered within the link I supplied, he provides a very simply implemented solution but also a very complex analysis and breakdown. Much of it is either superfluous to my/our application and also just plain over my head but after I got through it all a few key things became clearer. The question's involving the role of the reluctor/pickup in timing are valid ones but way too general and depend on so many factors that without applying it to specific hardware the only answer is 'possibly'.
What you're trying to accomplish by taking advantage of the variance in trigger voltage as it's produced by a reluctor type pickup at varying rpm ranges is in theory workable but I have a suspicion that you wouldn't get more than fractions of degrees without some additional circuitry. There's a pretty small voltage/time window in that curve where everything happens, The HEI module triggers on and off at about a .3vdc potential difference. It would help if the graph you supplied showed the actual time and voltages involved. I suppose you could try using a larger diameter magnet and larger gap to see if it would increase the duration of the on/off threshold...
This http://home.comcast.net/~loudgpz/GPZweb ... nNotes.txt is a good place to start...

One concern I had was whether the pickup coil would produce enough voltage (without supplementing it) to trigger the module at kickstart rpm's, but after playing around with it on the bench I think it will be ok.
Another problem could be in finding the trigger point for static timing, It needs velocity to work, might involve some trial and error... That's one reason I think the fixed magnet with a slotted rotating shield might be a better way to go.

[Jordan]

You could be right Bill.
You've got the test gear nicely arranged - could you spin the pickup with a variable speed drill? With a xenon timing light (the answer to checking timing when things need to move to get any action), you could do a rough check of speed related timing change. How about swapping the pickup coil connections, and getting some data?
I once made a high energy ignition from a kit that used a Motorola dwell extension chip, possibly what's inside your GM unit. Now the kit is sold with a programmable microcontroller in place of the previous chip.
One nice thing about inductive systems is that they can work without a battery.

Jordan

[DewCatTea-Bob]

" You could be right Bill. "

____ Back in the '70s, I had already been on-board with the same notion as Jason's reasoning... that the nature of the stock Ducati/Mototrans induction triggering-system also conveniently just simply happened to include the needed auto.advance characteristic (which luckily was able to be fashionable close enough for what the doctor ordered for an auto.advance-curve).
As I quite doubt that Ducati could get their hands on any affordable sophisticated ign.advancing electronic-technology way-back in 1972 .
__ Not knowing exactly how sensitive the pick-up's coil-sensor circuitry is to the weakest lines-of-flux (from the employed magnet-trigger), I can only suggest placing a sensitive compass near the stock magnet-rotor to see how far from the tip-end of the magnet itself, the compass can detect it,, or place the tip-end of it directly under a sheet of paper with iron-fillings spread-over it. _ Either method should display a good idea of how far ahead (in degrees) the flux-lines proceed the magnet's tip-end.
I'm betting that the results would show more than enough leeway to be responsible for our expected auto.advance-effect from the rotor-magnet.
__ On the other hand, I wouldn't be too awfully surprised if Bill turns-out to be right and the pick-up sensor doesn't react much more than a fraction of a degree difference.
__ I believe it would pay for Bill to conduct Jardon's suggested testing, cuz the results could possibly indicate another method for Bill to obtain the additional auto.advance range-span which he (& we) would like to obtain (for our DUKEs).


Hopeful-Cheers,
-Bob

[wcorey]

Oh no, more testing and fixturing! This was just an incidental side project and only implemented because I had the necessary hardware on hand, I'm not letting it turn into what the alternator thing already has.
Actually I already made and subsequently misplaced a mandrel to adapt the AAU to an air die grinder (more rpm's) as part of that experiment. Just as soon as I make another, I'll find the first one is how that will go. I suppose it could be easy enough to mount a magnet on a shaft and affix a pickup coil to something nearby.
I'll put it somewhere on the ever propagating to-do list...


Bill