Hei conversion question

Got my 80 ltd project still going, was going to stick to electronic ignition, dumping the ignitor box for gm HEI units (have five or six fromchevy stuff laying around)

Noticed on lou's (loudvhx) page he says to use coils of greater than 2 ohm resistance, but says on the honda conversion to use .5 ohm GM coils, and the general thought in the chevy world is to use .4-.6ohm coils (my camaro has a small body HEI i put together with a .6 ohm coil) so what's with the 2 ohms for the kz lou?

It's all about dwell. Look at the shape of the GM distributor's reluctor. Then look at the shape of the KZ's reluctor. Then, yet again, look at the shape of the Honda reluctor. (I only have images of the KZ and CB on my website.)

The GM reluctor is just a series of very sharp points. This produces very short dwell signal spikes. This means the coil has to charge very quickly. That is why it uses very low inductance coils. Low inductance coils also tend to be very low resistance as well.

The KZ reluctor is one big long lobe. This creates a very long dwell signal. This means the coil has a long time to build up a charge, so it can have a much higher inductance, and thus higher resistance.

The Honda is a combination of the two. It has a big lobe, but at the center is a small rectangular shaped protrusion.
This gives an overall similar affect of the KZ reluctor, where the dwell is considerably long. Thus the factory coils for the Honda were similar to the KZ. But the added spike gave more peak signal for starting, and also allows for a greater range of dwell. This is desired so you can have a more efficient ignition. This is why it was possible to come up with two designs for the Honda system; one that uses the stock coils, and one that uses GM coils. The major drawback of the Honda system is that the igniter has to compensate for a lot more crosstalk in the signals and thus has to be slightly more complicated.

The GM system uses an electronic dwell extension feature which requires the coils to be low-resistance in order to function properly, but is very efficient. But it requires more electronics to do the job. This is what the W terminal is for.

The KZ system uses a very well-designed reluctor shape to help control dwell for a decently efficient design, and very simple igniter design. A reluctor is just a slug of metal, and can't really fail. The KZ is probably the most robust/reliable system of the three. Being that the dwell control is inherent to the shape of the reluctor, the W terminal is ignored when using the HEI modules.

The Honda uses a combination of the two types... meaning it uses the reluctor shape to control dwell, but must use electronics to compensate for the crosstalk of the reluctor shape. When using the GM coils, the W terminal is ignored here too, but note the added complication of the start booster circuit required on some bikes.

With enough electronic manipulation, it's possible to use the low resistance coils on the KZ too. They are very cheap, like $30 each, but the problem is they are huge and heavy. I couldn't find any way to fit them under the tank on my 550.

To answer the question... the KZ reluctor is designed to make the dwell best-suited to the stock 2.3 ohm coils, so using lower resistance coils might work, but will generate much more wasted heat in the coils and in the igniter, with little added spark energy, so it's best to use a 2 ohm to 3 ohm coil.

Okay, so the single square protrusion on the cb ignition makes the difference, so either mod the kz rotor, fit the honda advancer mech, or just use a 1.6-1.8 ohm ballast with the auto coils.


Second question, if i were to use four mini coils, 2 per pickup, is that an additive resistance, say two 1 ohm coils equal 2 ohms resistance?

And yes, definately familiar with the GM reluctor ring, like i said, I milled out a points distributor, changed the top plates on the dizzy to use the HEI mech advance and electricals and fit it all under the cap on my 68, (not that i fully get how it works) but i did it to just do it and not buy a POS MSD

floivanus wrote: Okay, so the single square protrusion on the cb ignition makes the difference, so either mod the kz rotor, fit the honda advancer mech, or just use a 1.6-1.8 ohm ballast with the auto coils.

It's not just the protrusion, it requires a possible booster circuit to raise the bias on the pickup signal temporarily during startup. This can be an issue if kickstarting, because that booster circuit is controlled by the starter circuit. If there is no starter circuit, there needs to be some other method of raising the bias... and there are some potential methods for that, like sensing the battery voltage or using a latch based on the first upshift from neutral, etc.

It would be easier to put together a few resistors and diodes than to try to machine some mechanical parts.

floivanus wrote: Second question, if i were to use four mini coils, 2 per pickup, is that an additive resistance, say two 1 ohm coils equal 2 ohms resistance?

In series, yes. ( In parallel, they would be .5 ohm total.)
But in order to use mini coils, you have to really control the dwell properly. They can go bad very quickly if the dwell is not controlled properly. They just don't have the physical size to dissipate the extra heat of dwell that is too long. Also, at high RPM, the dwell may end up too short since you will only be using 6 to 7 volts to power the coils.

Do you have specific coils in mind? And are the specs published for them?

If you are considering the GM coils used with the Honda CB mod, I may already have some sort of circuit for that. I'll have to look. If you can fit the coils, physically, that's the way to go since they are dirt cheap and available at any parts store.

I've got scores of GM and dodge neon coils left over from my car tech days. So of course that would be the cheapest method of course. (Plus i think the neon coils are $16 shipped now, with replacable high quality wires available)

Doesnt seem that any of your diagrams use the W terminal which normally goes to the reluctor along with G. Would that be part of the issue with the low impedance coils?
Or is it because of the different style ignition pickup?

I really like the Neon coils. They were also too big for me to use, but that's what I would have used over the GM coils if I could have.

The W terminal is the dwell extension terminal. It extends dwell by raising the bias (aka offset, aka DC level, etc) to the pickups. Since the KZ does this by the shape of the reluctor rotor, the W terminal is not really needed when using the KZ pickups (with stock coils). And, I will have to review my notes on the subject, but there might even be a chance the W terminal is not needed when using the Neon coil. But then the external bias circuit would have to be designed accordingly. There might even be a way tlo use the W terminal and modify its behavior with external circuitry to get a proper dwell for the Neon coil, without using ballast.

The W terminal is used, and modified by external circuitry, in the HEI conversion for Honda CB's using stock coils. It is also used, incidently, with points when using the points as a trigger, but that is simply as a pull-up circuit.

As a side note, the 4 pin HEI has a current limit (it's sometimes called a current hold) circuit that limits at about 5.5 amps. What this means is, the igniter, itself, becomes a variable ballast. This sounds great, except the heat generated in such a ballast is very high. Extended current-limit use will fry the module (because it is only meant to be used momentarily, and not necessarily on every cycle). That's why ballast resistors tend to be so big and made of ceramic casing. They get hot! The HEI is not meant to handle the amount of heat a big ballast might handle.

For arguement's sake, lets just say I use the HEI plan you set forth, with the neon coil and jus toss a 1.8 OHM resistor on the circuit (probably out front like where an oil cooler would be) would that be the easiest banaid to the siuation?

Or would that just be a bandaid, it wojld reduce the output of the coils, but they should be good with just normal 8mm wires and NGK plugs correct?

It would be the easiest, but I don't know if you'd get the full RPM range. Once you get to 10k RPMs, you only have about 2 msec to charge the coils. The Neon coil might want as much as 3 or 4 msec for max spark, when 14v is applied. Once you cut it down to 4 or 5 volts (due to the ballast), you are really cutting down the current in the coil. But it doesn't need to be so much resistance. I think you could get away with a 1 ohm ballast and that would help things a bit, that would get you up around 6 or 7 volts to the coil.

It will only reduce the output at higher RPMs (which does happen in most systems anyway). But yes, I consider it a bit crude. Far better to just give the coil the dwell it wants and not waste so much energy as heat.

Certainly, if you already have the parts laying around, you can play with it and see what happens. I would suggest using two, 1-ohm, 50 watt resistors. One in each circuit. OR one 1-ohm, 100 watt resistor in series with the common wire on the Neon coil. (The Neon coil I have has 3 wires. One is the positive common wire, and the other two are the negative side for each coil. I might have a diagram somewhere.)

Since the 1-ohm in series will allow a potential current to be around 7 amps, the current limit in the HEI modules will come into play. This means the HEI modules must be mounted to good heat sinks with heat-sink compound.

If you mess around with it, then you'll already have the wires and mounting etc. done. Then if you want to make the adapter circuit later, it will be an easy conversion. The Neon coils are closed-loop cores, so it doesn't matter if they are mounted to a piece of steel or aluminum, and the coils don't need any electrical grounding.

Yes, normal wires and stock plugs will be fine. Best to use stock plug gaps for testing. Larger gaps stress everything more. Once it's running, you can test the gap for larger openings if you want to mess with that.

Luckily for me I have a foot or two of 2"x 1/4" Thick aluminum bar from when I made my shock mounts, and yes the neon coils have a 3 wire setup, one common feed and two seperate triggers.

and yes, I do agree that ballasts are a bandaid fix (the one on my 77 gl1000 drives me nuts, why stock does it have to be there? Oh well, I digress) and in the end rob you of at least some potential power. Of course I could always order a set of coils from Z1 and be done with it, but I don't quite see the fun in that

No fun if you already have good Neon coils laying around. I wish I could fit mine on the bike. That's $150 worth of coils for $16.

I'll dig through my notes and see if I can come up with a ballast-free, simple circuit.

Absolutely, and if anything goes wrong, you can get them easy as you please, even the local bike shops (one a kz FREAK) don't tend to stock the proper coils, and the ones they do, tend to be of dubious quality.