Topic: D8EA and DR8EA spark plug resistance

[69cb750]

D8EA 29,000 volts in plug wire
DR8EA 5000 ohms resistance (resistor plug) 12,680 volts in plug wire
Spark plug cap resistance unknown (you can probably guess)
Resistor wires, resistor caps, resistor plugs are used (not all at same time) to reduce electromagnetic interference (EMI).
In 1964 or so a particular car (same car, year, make,model unknown) would go by our house producing there horizontal lines in our tv set.

[Don R]

 I could predict my brother coming home in his 55 chevy when he was two blocks away by the TV screen. He had solid core wires and rajah plug terminals.  Later he began using a delco distributor rotor for a Studebaker because it had a resistor in it and it fit the chevy.

[TwoTired]

Wasted a half hour watching that video.   All just to verify that field modifications (resistor plug) used in a CDI system that specifies Non-resistor, doesn't work as well as the system does with the proper parts installed.

Affable presenter with a total misunderstanding of how the system works.  Myopic narrow view of only one parameter of electricity (voltage), totally ignoring the current in system.  Essentially ignoring basic ohm's law.  As an engineer, he makes for a good parts changer mechanic, oblivious to working theory.

Very good example of junk science and using good tools that give information that is easily misinterpreted by the uneducated/unprepared.

CDI is an early type of multiple spark ignition.  In order to repeat that spark initiation event, the capacitor must be discharged to a level that causes the circuit to recharge it again.  This means that current flow is critical to make that perform as designed with correct timing within the event.  Added resistors impede that capacitor drain time, altering circuit parameters and expectations.  The waveforms show that multiple spark initiating events are diminished and more erratic when using the resistor plug.  Not so surprising, to me.

While he mentions that a fueled atmosphere aids spark, he goes out of his way to prevent fuel from being added, further deviating from actual run conditions.  I don't know the specifics of this particular CDI circuit configuration, and neither does the presenter.  But, the total duration of spark may be controlled by the CDI unit control, and not just the coil depletion characteristics, as would be the case for the Kettering design in our SOHC4s.

The fact that the resistor plug reduces the peak voltage is no surprise either.  That's what they do, in order to extend the discharge time of the total spark event, and redistribute the available energy from that peak into the broader total spark event. 

CDI ignition operation is fundamentally different from our Kettering type ignitions.  I like them a lot.  But, any takeaway from this video or post is largely irrelevant to how our SOHC4 ignition systems actually function, and what is needed in the chamber for an acceptable spark event. 

With a fixed non-rechargeable initiation event like the SOHC4 has.  The peak energy of initiation is reduced by added resistance, the coil's stored energy is then delayed and redistributed to form a longer overall spark event duration.

In an electronic circuit, it is best not to alter the design parameters beyond what was engineered, at the risk of it not working as designed.   If you really think higher voltage is always a good thing, plug your bike into a wall socket and see how much better it works with that higher voltage.  Wear eye protection, though, to better see the total result.

Cheers,

P.S.  The video complains about poor bike performance in the video.  He never tested the bike again to see if his higher voltage theory ever made an effect on his actual "pig" bike performance.  His whole point of the video "show" was to impress the viewer with his new scope toy and presents only the data that supports his assertion that higher voltage is better.  Which I can only assume was his going in assumption.

[PeWe]

My CB750 had NGK resistorplugs in the 80's. Caps had 0 ohms. Stock coils
Today NGK 5 kohm caps and D8EA or Denso X24ES-U non resistor plugs. Dyna 5 ohm coils.

[Deltarider]

That's what they do, in order to extend the discharge time of the total spark event, and redistribute the available energy from that peak into the broader total spark event.

You make it sound as if you have actually witnessed it. Why don't you show us instead of galopping away in language the like I've never seen in all the shelf of my automotive literature, not to mention the 8 vol. Steinbuch and Bosch tutorials at the polytech.

The peak energy of initiation is reduced by added resistance, the coil's stored energy is then delayed and redistributed to form a longer overall spark event duration.

We are dying to see this beautiful long spark event. Where is it?

[TwoTired]

That's what they do, in order to extend the discharge time of the total spark event, and redistribute the available energy from that peak into the broader total spark event.

You make it sound as if you have actually witnessed it.

I have.

Why don't you show us ...

You don't pay me enough.  ...and you are unable to learn.

The peak energy of initiation is reduced by added resistance, the coil's stored energy is then delayed and redistributed to form a longer overall spark event duration.

We are dying to see this beautiful long spark event. Where is it?

Somewhere you are too inept to find.

[dugsgms]

  Video certainly illustrates what the poster was going after, the difference in voltage at the tip between a resistor and non-resistor type spark plug. Unfortunately, the voltage at the tip has more to do with the physics of the secondary system than what is required to light the fuel air mixture, but at least he went to the trouble to record and show both patterns so we could see them. Would have been somewhat more informative if he had shown them on a bike that was running and at proper system voltage. I suppose the addition of a resistor could cause misfires if the secondary system wasn't able to provide the additional voltage required due to the addition of the resistor but the system would have had to been pretty close to its max output even before adding the resistor into the system and the resistor would only have been exasperating a previously existing problem.

[PeWe]

I'm sure there are differencies as discussed. Most important conclusion is based on practical  experiencies on these old CB's.
Fuel is different so what worked fine before might not be same today.
Coil, HT lead, cap and plug make a combination and end result to be found to work fine on  CB500/550/750 street & touring. Ignition type might change a little too.
Racing has probably another combo.
My CB 750 (836) ran worse (like colder plug) on Iridium R plugs than stock type NGK D8EA. This with Dyna 5 ohm coils, copper leads, 5 kohm caps.

[TwoTired]

  Video certainly illustrates what the poster was going after, the difference in voltage at the tip between a resistor and non-resistor type spark plug. Unfortunately, the voltage at the tip has more to do with the physics of the secondary system than what is required to light the fuel air mixture, but at least he went to the trouble to record and show both patterns so we could see them. Would have been somewhat more informative if he had shown them on a bike that was running and at proper system voltage. I suppose the addition of a resistor could cause misfires if the secondary system wasn't able to provide the additional voltage required due to the addition of the resistor but the system would have had to been pretty close to its max output even before adding the resistor into the system and the resistor would only have been exasperating a previously existing problem.

Perhaps you missed the point that a CDI  (Capacitive Discharge System), needs to have its capacitor discharged rapidly, to perform it's multiple spark function.  It has an internal voltage converter and oscillator to perform a recharge of the capacitor during the initial spark event.  The added secondary resistance impedes capacitor depletion, so it can't recharge the cap for the next inline spike properly due to internal timing mismatched with the voltage decay rate.  I also have suspicions that the waveforms shown, were not at all consistent, leading to questions of whether the CDI was in fact failing and in need of replacement or repair. It was not a new bike and known to have misfires.  Never proven was if the spark plug change alone corrected that issue.  The viewer was expected to make that leap of faith, that the resistor caused the problem.  It was never proven.  It is also possible that the added plug resistor lead to the partial failure of the CDI unit, as it was forced to work outside of design parameters.

Because it was a CDI system, the peak voltage change was actually irrelevant.  But, your right, he (inadvertently) demonstrated that added series resistance will reduce the peak initial spark starting event.   But, what he completely overlooked was why, and its actual effects on combustion initiation.  Rather he fell back on the old standard of what it looks like, and a more-is-better standard without actual proof of that being so.

Some engines do actually need HV spark.  That does not mean all engines need that.  The stock SOHC4 is one that doesn't need HV spark.  It just needs enough to begin the flame front and with a spark duration approaching the piston power stroke duration at peak RPM.

The video presenter is a parts changer, not a qualified analyst (even though he has some analytical tools).  He chose to replace a spark plug, as the numbers weren't correct.  He never proved it to be a causal effect, as the actual complaint about bike run issues was not demonstrably solved.   My guess, with the data presented, is that he'll replace the CDI unit next.

Cheers,

[Bodi]

You can lead a horticulture but you can't make her think...

I'm missing the point of this, and agree that some actual tests with a running engine would be way more useful than showing off his new scope. And any CDI ignition can't be directly compared to a basic Kettering system.

Nor can one directly compare a car engine ignition to an SOHC4. The distributor, resistance wires, single ended coil... they are similar but major differences. A car coil works harder than our bike coils: a distributor V8 with 6,000 RPM at redline is sparking 800 times a second (!). Coil on plug systems allow a much smaller coil, each only sparking 100 times a second at 6,000 RPM.
Resistor wires on cars are pretty much only for RFI suppression, there's no specific resistance value since the wires are all different lengths. Coil on plug probably uses resistor plugs, I don't know. There should be little or no RFI from them, since there is no or almost no HV cable for an antenna.

The SOHC4 coils fire once per turn, so at 10,000 RPM that's 166 times a second.

The resistor plug or cap does extend the spark duration, in practice I'm not sure they make much difference. I've tried with and without (I have a selection of caps and plugs) and found zero performance difference except with resistor plugs AND caps I had some misfiring at high throttle midrange RPM. Since there are two plugs firing on a coil that's a lot of resistance. Sadly, I don't have an ignition scope to show the voltage or current. I do have a nice oscilloscope but I'm not too keen on connecting the input to thousands of volts.

[TwoTired]

The resistor plug or cap does extend the spark duration, in practice I'm not sure they make much difference. I've tried with and without (I have a selection of caps and plugs) and found zero performance difference except with resistor plugs AND caps I had some misfiring at high throttle midrange RPM. Since there are two plugs firing on a coil that's a lot of resistance. Sadly, I don't have an ignition scope to show the voltage or current. I do have a nice oscilloscope but I'm not too keen on connecting the input to thousands of volts.

The 550 is the only SOHC4, that came with 10K plug caps.  (OK, there was a Canadian 750 import that had them, too.)
Anyway, the 550 is also the only one with D7 heat range (hotter).  So, one can expect hotter firing condition in a CB550, as opposed to the 750, which uses the more prevalent D8 heat range.  We all know that the spark electrodes wear down over time.
With knowledge of EDM systems which erode metals with a spark discharge, and applying that to the SOHC4, we have a normally hotter environment with spark discharge.  If we reduce the current to the electrodes, the discharge erosion effect should be diminished.  I believe that is the rationale for the 10k caps on the CB550.  Moreso than the secondary effect of longer spark duration.

Extending the spark duration is not so much a noticeable power improvement.  But, more of an efficiency contributor.  If extending the spark duration accounts for 1% economy improvement because of slightly more complete combustion some would say that's worthwhile.  Something you'd feel more in the pocketbook over time than the seat of your pants while riding.

It's funny.  There are posts on the forum about eeking a little more power from the motor, in a number of ways.  But, actual ignition refinement is poo pooed, unless the refrain "MORE voltage" is automatically applied.  Like that's going to add HP to the motor.  Ignition systems draw about 20 30 watts, (which the alternator has to make from the engine crankshaft).  Even if we assume all of that was delivered to the combustion chamber, a 45 HP engine produces 33,750 watts.  Hi voltage ignitions usually add another 10-20 watt draw (which the alternator still has to produce).  How could you possibly notice a 10 watt engine output improvement from a 33,750 watt motor?   Not that any of the spark power actually contributes to HP out of the motor.  The fuel is gas and air, not spark power in any sort of way.  Spark is just the catalyst for the fuel/air, and a means to control when combustion starts.

For your scope, don't forget to use a voltage divider on the input, and be mindful of maintaining a good spark gap isolation, so it doesn't bridge past or around your resistors.  Creepage and clearance rules.

Cheers,

[dugsgms]

Perhaps you missed the point that a CDI  (Capacitive Discharge System), needs to have its capacitor discharged rapidly, to perform it's multiple spark function.  It has an internal voltage converter and oscillator to perform a recharge of the capacitor during the initial spark event.  The added secondary resistance impedes capacitor depletion, so it can't recharge the cap for the next inline spike properly due to internal timing mismatched with the voltage decay rate.

  Hmm, I seem to remember from my dirt bike days the it was recommended to use resistor plugs, wires or caps in a CDI system as non-resistor were more prone to damage the CDI box....maybe I'm remembering wrong.

[TwoTired]

  Hmm, I seem to remember from my dirt bike days the it was recommended to use resistor plugs, wires or caps in a CDI system as non-resistor were more prone to damage the CDI box....maybe I'm remembering wrong.

The CDI circuit can be designed to accommodate or even require additional secondary resistance.  It this case the claim was that non-resistor plugs were specified for the particular bike in question.

Just like not all ignition systems are the same, neither are CDI specific designs.  It's an electronic device.  Most electronic devices have different design circuitry.

There is also the question that ignition systems outside of this discussion are often called CDI by the misinformed, but really aren't.  Even though they are electronic switch devices, or EI boxes/ignition boxes, referred to as CDI as that was a popular term during some eras.    They are all black boxes with something inside that makes spark possible.  A tissue is often referred to as a Kleenex, even if it isn't that particular brand.  How many times have you made a Xerox of a paper on a machine made by another manufacturer?

Cheers,

[Tracksnblades1]

You can lead a horticulture but you can't make her think...

I'm missing the point of this, and agree that some actual tests with a running engine would be way more useful than showing off his new scope. And any CDI ignition can't be directly compared to a basic Kettering system.

Nor can one directly compare a car engine ignition to an SOHC4. The distributor, resistance wires, single ended coil... they are similar but major differences. A car coil works harder than our bike coils: a distributor V8 with 6,000 RPM at redline is sparking 800 times a second (!). Coil on plug systems allow a much smaller coil, each only sparking 100 times a second at 6,000 RPM.
Resistor wires on cars are pretty much only for RFI suppression, there's no specific resistance value since the wires are all different lengths. Coil on plug probably uses resistor plugs, I don't know. There should be little or no RFI from them, since there is no or almost no HV cable for an antenna.

The SOHC4 coils fire once per turn, so at 10,000 RPM that's 166 times a second.

The resistor plug or cap does extend the spark duration, in practice I'm not sure they make much difference. I've tried with and without (I have a selection of caps and plugs) and found zero performance difference except with resistor plugs AND caps I had some misfiring at high throttle midrange RPM. Since there are two plugs firing on a coil that's a lot of resistance. Sadly, I don't have an ignition scope to show the voltage or current. I do have a nice oscilloscope but I'm not too keen on connecting the input to thousands of volts.

Is that V8 a 2cycle....?

But even at only 400 per second, it's still kickin it.  👍