I suppose one could use a relay to insert a ballast resistor into the coil +B feed. That would limit coil current whenever the starter is cranking.
Just the opposite to what my MGB does. The MG uses a relay to remove the ballast resistor during start up in order to give the coil extra "juice".
P.S. My 750 Turbo ignitor came yesterday.
loudhvx wrote: Ok so I was able to do a few runs at work. My buddy at work helped me get things setup, but we were still rushed so this is really only preliminary.
The ZX dwell is quite a bit more efficient than that of the KZ. At 1000 RPM the dwell is about 6 msec (quite a bit better than 17 msec). At 10,000 the dwell is the expected 2 msec.
However, below 1000 RPM, especially during startup type RPMs, the dwell is longer than 8 msec. I measured roughly 10 msec at 450 RPM. So that makes startup using an LS1 possibly problematic. Then again, maybe it won't matter. The spark will be coming about 2 msec early, but that's out of 120 msec for a rotation. Still, I'd rather not have early sparks during startup.
A couple side notes I noticed... unlike the KZ, the ZX ignition is not two independent ignition circuits in one box. Both pickups must be connected and functional in order for the dwell to work properly. With the other set of pickups not connected, the dwell drops to being very short. At times it drops well below 1 msec.
Also, unlike the KZ, the ground side of the pickups appear that they may be able to be swapped. That is, it appears the negative terminal of the pickups are simply hard-wired to ground.
I'll have to look back at the video (I'll post it after I edit it down hopefully with some screen shots) , but I think the igniter box alters the shape of the pickup signal. So how the pickup signal looks will depend on whether it's connected to the igniter or not.
I forgot, I didn't include the pickup signal in this set of recordings. Their traces were distracting from the coil signal trace.
Notice the dwell is not exactly a function of RPM. That is, it depends on the dynamics of the RPM as well. The dwell at a given RPM may be longer or shorter depending on if the RPM is increasing or decreasing. However, this might not be so drastic on a real engine. The air motor can change RPM much faster than a real motorcycle engine.
I guess I should point out for anyone else coming across this post, the portion of the signal showing the dwell is the small horizontal section at the bottom of the trace. That is what is being measured. The dwell is the duration during which the coil's negative terminal is connected to ground. The rest of the time, it is floating up near battery voltage.
I should also mention, in case it matters, this was running from a 12v battery measuring about 12.5v. That's a bit lower than a running bike. If the supply voltage effects the operation of the igniter, that will have to be looked at more closely later.
I bought a used 750 Turbo ignitor off eBay to use on my bike.. Better for boost because It limits max advance to 30 degree.
I can confirm, the zx750 ignitor is a direct plug n play for the zx550.
It's up and running on my bike.
However the ignition rotor does need modification to match the ignitor. It needs to trigger max advance at 30 degrees BTDC.
Easy to do.
No time for test ride today but It should actually run stronger on boost with less advance.
And also less likely to detonate or ping on pump 93.
I've also switched to the 550's original TK carb rack which had been perfectly jetted for my pre-turbo engine.
Following what I had to do with the CVK carbs, I've made the equivalent changes to the TK jetting. With 10 lbs boost, carburetor size is not a concern.
Jetting should be right on but I can fine tune it as needed.
The TK carbs have a much better low speed circuit. They've always worked better than the CVK at low speed..
Cold start circuit too. In fact the small spark plug gaps (.022) don't cause any cold start problems with the TK carbs mounted.
Instant start and smooth running on and off cold start. Better fueling.
Fuel metering is perfect with the TK carbs and the 750 turbo ignitor's 30 deg total advance is much better.
I'm running pump 93 with no problems.
Had a small problem yesterday on the first run.
The TK has a "choke" rod you pull out and the cold start plungers open on all 4 carbs.
It has a spring loaded detent to position it but it does not have a return spring. Nor is there a good place for a return spring.
It fully opened under boost. Pushed right open by the pressure. An oversight on my part.
I've since made a mechanical stop that keeps it closed. It has a spring loaded release lever to allow pulling out the rod and then automatically lock it down when you push the rod back in.
No problem after that.
With the new advance curve, power is less on-off.
Boost builds smoother and more predictably and it still builds just as much.
I was on a nice straight back road with 30 mph posted but no traffic and very few houses .
5th gear at 4000 rpm is 45 mph, then rolling on the throttle quickly had me at 103. That's when I shifted to 6th and backed off the throttle.
I'm using a GPS app for a speedometer and it captures top speed. I wasn't looking at the speedometer.
As a comparison..
I had an 07 Bandit 1250 that made 124 RWhp on the Dyno. with just a few mods. It had way more torque but this GpZ is quicker.
I ultimately added nitrous to the Bandit and ran a 25 shot which dyno'd at 150 hp. The GpZ is quick like that. The Bandit was much heavier.
I also ran the Bandit with a 50 shot. The Gpz isn't that quick.
I'd like to replace all the oil cooler and fueling lines with braided hose and AN fittings before I do any long rides far from home.
And the lower fairing needs to be mounted.
As for ignition miss at high rpm and boost, I'm leaning toward the following solution.
I'm going to feed 19V to the coils but use a ballast resistor in series to limit current. That way the coils won't overheat/stress at low rpm when dwell time is high.
I'll also use an RPM window switch and relay to bypass the ballast resistor at high rpm.
At higher rpm, when dwell time is low, the coils will receive the full 19V. Coil current will be higher and it should produce a better spark under boost.
The simple solution would be to supply the coils with 19V without the ballast resistor and window switch.
If I knew the coils and ignitor could handle the extra current I would do that.
I would say running 19v all the time, when the coils are cold you will easily get above 5.5 amps on the coils at the lowest RPMs. As the coils heat up, that max will drop below 5.5 amps due to the coil's resistance increasing.
So at first this would appear to be getting too close to the 6A limit of the Zx tansistors. But really, the duty cycle is very low at low RPMs so the average current will be nowhere near 5.5 amps. The average maybe a tenth to a quarter of that.
So how time-sensitive is the transistor to that 6A amp limit? Hard to say, especially because they are so old to begin with.
If everything was new, and replacements were easy to get, I would say just run straight 19v.
Another option would be to run the Zx ignitor output into two 7-pin HEI modules using a little inverter circuit. Then run the 19v to the coils all the time. The HEI's internal current limiter will protect the coils and you might even get a bit higher voltage on the spark if needed. They are plentiful and cheap. If the coils can't spark for some reason, at least the Zx igniter will be protected.
So we should probably talk a little about voltage (for anyone else reading this, that is). The output voltage of the coil, whemn spark successfully occurs, is actually determined by the air-gap at the plug and the pressure in that gap.
Bigger gap = higher voltage.
Higher pressure = higher voltage.
During the spark discharge, the coil is essentially just a big step up transformer.
The voltage at the plug is just a stepped up voltage of that found on the input side of the coil.
If we call the spark voltage high-voltage. Then the voltage at the input of the coil is still relatively high. It's usually a 100:1 ratio.
In practice the voltage on the input (primary) side spikes to anywhere from 300 to 600v depending on what the plug's voltage was.
If the coil fails to spark due to insufficient voltage, there can be several failure points.
First is a breakdown of the insulation in the coils or in the plug wires etc. There is not much you can do about that except to replace damaged parts.
Second, and this is usually the weak point of flyback ignitions, is the peak voltage that the output driver of the igniter can sustain while preventing current flow. The driver will be damaged if that limit is exceeded, so there is always a safety circuit that limits this voltage. That is where you see the 300v to 600v limitation imposed. In our case it's about 450v on the Zx ignitor. That's going to be similar on the HEI module, but if you can get an extra 50v on the primary, that's an extra safety margin of 5000v on the plug. Of course, there is a chance the HEI module has a lower limit due to car engines not being very high compression, but hopefully 40 years of tech improvements means better performance from newer products.
CDI does not have this associated limit. The cdi system produces the relatively high voltage during a time of no-current so it is easier to hold back the voltage. Then this voltage (300 to 600v) is just dumped into the coil which was sitting idle waiting for current. With CDI, the voltage concerns are really only related to what the coil itself and the plug wires can handle. (Of course, as mentioned, CDI has it's own problems at low RPMs, though, because the sparks have very short duration. )
My concern, as I already mentioned above is that if you are experiencing troubles with sparks and have already reduced the plug gap, it's possible you are reaching the voltage limit of the ignitor. In that case, adding a lot more coil current might not be a real solution. I haven't directly compared voltage limits of Kz or Zx ignitors to HEI since that usually involves destructive testing.
I like your idea about using 2 HEI modules to isolate the zx ignitor from potential overload.
I had to replace the 4 pin HEI module on my MGB and I think I paid $19 for it.
Here's the datasheet for the Fugi power transistors in the ZX ignitor.
There's some reference under the electrical test conditions section that references a collector current of 8 amps.
Not sure what it's talking about.
I was still editing the post above (lazy way of not losing a post in case of a server drop).
I'd be happy to draw up an inverter schematic to drive a couple 7-pin HEI's if you want to try it. Back in the day, you would only have to walk to the nearest Radio Shack to get the parts.
The collector of the transistor is the connection to the coil so that is the current we are concerned with. Data sheets get updated all the time, so you need a version from the 1970's when the part was being designed and starting manufacture. The modern version of the same part can probably handle a lot more than the older version. So specs are subject to question.
6 amps sounds more realistic from that era based on the size etc. The first version of the HEI used a current limit of 5.5 amps approx. Another factor is wattage. You can assume there will be anywhere up to about 1.5, maybe even 2 volts on the transistor when there is 4 to 5 amps flowing. So worst case is 10 watts for a short moment, and I assume the transistors can probably handle several times that.
Since we are talking about transistors, and I don't get to talk about transistors very often, ever, I should mention that the output transistors of igniters are not just a single transistor. It is actually a small integrated circuit emulating a transistor.
Notice the spec sheet shows a small diagram of the internals. In it you see two actual transistors. Those are called a Darlington pair. Most single transistors can give high voltage or high gain, but almost never both. It takes a pair to do that. Notice there is also a Zener diode (Z-Di) shown. That is part of the internal voltage protection I spoke of earlier.
Notice the voltage limits are in parentheses (450). I think that is because the internal limiter is limiting to 300v. The spec in question is Vceo(sus). "Sus" means sustained. So the transistor can only hold back about 300v for a sustained time. That's typical of these things from that era. But the voltage spike during spark initiation is extremely short, so the overall transistor can hold back much higher voltage for that very short time.
That pdf appears to be from 1999.
Nowadays the Darlington BJT pair IC has been replaced by a four-layer device known as an IGBT. That is a combination of FET with BJT output. In my experience, the performance is better and more efficient. but the older Darlington is more robust... harder to blow up unintentionally.
This is turning into an electronics symposium where each answer prompts another question.
Here it is.
Using a ballast resistor to limit current not only drops voltage but the voltage drop increases as resistor temperature increases.
Is there a simple transistor circuit that, if placed between the ignition coil and the ignitor, would limit current to say 5A?
Assuming there is a simple circuit, would it dissipate power by shunting to ground? it would need hefty current and thermal limits.
Or rather than place a device between each coil and the ignitor, place a single current limiting device between the power supply and the 2 coils.
The HEI module solution would limit current and isolate the ignitor but I thought an even simpler device could be used to just limit the current.
Another solution would be to open up the ignitor and replace the Darlington Pair devices with newer higher capacity versions. That's not my 1st choice as there's risk of damaging the ignitor and a different Darlington Pair may upset the rest of the circuit.