Topic: Resistor vs non

[beemerbum]

Can I substitute a NGK D8E with the resistor version in my K1 750? Is the spark affected.

[ekpent]

 I use just standard D8ea plugs in my bike. Do you have stock style resistor caps. Be interesting to hear some other theories on this from the techie people. Here are some musings to get you started on your search  http://forums.sohc4.net/index.php?topic=173263.0

[TwoTired]

Yes.  The spark event is affected with a change in circuit resistance.  The higher the resistance, the longer the spark duration.  Provided the coils have stored enough energy to last longer.  And the spark event will be reduced in peak current. (So spark less hot)

Have you checked what resistance your plug caps currently have?

You may not notice any difference in the engine run , and your plugs may last longer due to the reduced current.  But, the circuit may be more demanding on points and condenser health which determine what energy gets stored in the coils.

On the other hand, start up can be less vigorous,  as the starter draws down the voltage powering the coils, making energy storage more scant.  Likely worse under colder conditions.

Cheers,

[Deltarider]

For those worried about the duration of the burn time, just choose the minimum plug gap Honda recommends. I have 0,6 mm. In theory the result will be: less voltage required for the initial spark peak which leaves more energy available for the burn time. But I wonder, if you will ever notice the difference.

[TwoTired]

Be aware the spark event duration and engine burn cycle duration are two different factors.  The spark gap determines voltage required to begin the spark event.  Not how long the spark event initiates or involves the burn event, whose duration is determined by other factors.

This applies to the Kettering style ignition used on the stock SOHC4.  Other ignition schemes can change both the voltage and spark duration by design control.  …still independent of the burn event duration, though.

Studies have shown that a larger spark gap, requiring more voltage to initiate, does a better job of involving the materials consumed in the burn event for a more complete and efficient burn cycle.  It’s kind of like starting a fire with a blow torch instead of a match.  It is an important distinction during high RPM operation, when burn cycles must be shorter.  Modern electronic ignitions in today’s vehicles all employ a much larger spark gap, for both power and fuel economy.

Cheers,

[Deltarider]

We can dilate upon all kinds of combustion engines, our motors, even in stock configuration have a more than adequate ignition system. 'Burn time' is not the term for combustion, but refers to the period the plug is still sparking after the initial peak. In the pic it's the elevated line, right after the spike, that here has a duration of 2,51 ms.

[TwoTired]

The scope picture shows spark arc duration where current is flowing, not combustion burn duration.  The spark event only starts the air/fuel burn, it doesn't define the duration of the burn of combustible materials in the cylinder.  The fuel burns until the conditions to support the burn expire.  It needs no spark after the burn begins.  That's simply how our subject internal combustion engines work.

The duration of the spark event on the scope picture is defined by how fast the depleting stored energy in the coil can maintain the plasma channel arc across the spark gap.  This is the only time period where the circuit is actually complete and current flows.  At all other times the coil secondary components only have voltage potentials and resistance is irrelevant.  Circuit resistance defines how fast the stored energy is allowed to be released, once the plasma arc is established.  The spark event ends when the stored energy in the coil allows the voltage to fall below that required to sustain the plasma arc across the spark gaps at which point current flow stops.

I don't know what circuit your scope picture applies to, or the circuit component structure it is monitoring.  But, if you change the circuit loop resistance, the spark event duration will also change, as that will allow more or less current to flow in the arc channel, and ultimately the drain rate of the coil's stored energy.   Circuit resistance acts as a valve to control the release time of that bucket full of energy.

Cheers,

[maxheadflow]

TT is correct.  Spark duration is the width of the 280 volt peak and maybe some of the ringing (not all)..  Burn time on the scope looks more like points / driver open time.

[Deltarider]

Frankly I don't see how my post could have caused confusion. Yes, burn time is not the same as the combustion period. Who said it is? Burn time is the technical term for the spark duration that follows the initial spike. For those interested, the scope image shows the performance of my homebuilt transistor ignition that has been on my bike since the late 90s. Test was carried out by engineers who have tested several EI's for a club of vintage sportscar owners. The unit has proved utterly reliable, provides a short rise time of less than 25 µs and a burn time of over 2000 µs. IMO, there is nothing extra to gain by having other pricy aftermarket EI's. I choose for this one, because in those years I used to travel to far away countries and I wanted to have a back-up when needed. I can return to the old system within five minutes, if ever the module would fail. It never happened. The breakerpoints live forever and now have served some 60.000 kms. The first kit I assembled, was on my Peugeot 504 GL, that has succesfully crossed the Sahara desert with it.
First pic shows the measured primary rise time, here some 20 µs. You can have it even shorter, but then you must omit the kit's 0,22µF capacitor. Personally I'd rather not, because it may result in multiple firings and funny results on your electronic tacho  Burn time is plenty: 2500 µs (Bosch super coil, the red one). In the test burn time extended over 36^o @ 3000 rpm (2 ms). The second pic just displays the total of what happens in the primary circuit.

[maxheadflow]

The first picture should be the spark time but I don't see any residual ringing. The second shows the spark as a narrow pulse, tank circuit ringing / decay and dead time.

This actually brings up an interesting question on Hondaman's ignition.  The the points only seeing 12v, can the gap be closed say down to 0.010" to increase the dwell?  Points shouldn't burn at that voltage and get a little more core saturation time at higher RPMs.

 

[Deltarider]

Burn time on the scope looks more like points / driver open time.

I'm afraid I don't quite understand what you mean. If you mean to say it looks like just a conventional kettering breakerpoints ignition, I don't see the line oscillate through the 0-axis, do you?

The first picture should be the spark time but I don't see any residual ringing.

The first pic is just a single shot of the rise time, the time the coil is being saturated. Here peak is reached within 25µs.

The second shows the spark as a narrow pulse, tank circuit ringing / decay and dead time.

The second pic shows two complete cycles. I don't know what you mean by 'a narrow pulse'. Burn time, here 2,5ms, is represented in the graph by the elevated line between the initial spike and where the line drops to 0, where the spark duration stops.

This actually brings up an interesting question on Hondaman's ignition.  The the points only seeing 12v, can the gap be closed say down to 0.010" to increase the dwell? Points shouldn't burn at that voltage and get a little more core saturation time at higher RPMs.

Voltage is irrelevant, current is. I don't know about Hondamans, but as far as the control current - if you insist on talking Volts - my breakerpoints see only 6V max. I see no advantage in increasing the dwell. On the contrary, why have the, in my case, 3Ω coils switched on, longer than necessary, waisting energy? For what? With even a standard dwell, measured in Duty Cycle: 52-53%, bike pulls like a rocket well into red zone. Which brings me to: if I must say something nice about an aftermarket EI, it is that simple generic Tytronic, where the designer at least has been smart enough to limit the duty cycle to 50%, whereas Dyna... But 'more' will always sell well in some markets...

[PeWe]

When at it...
Smallest or widest gap as Honda recommends?
0.6 vs 0.7mm
I have set my plugs to 0.7mm most of the time. Lately 0.6mm on one bike when I thought that higher compression might like smaller gap better. Just a guess.

Dynatek 5ohm coils.
Non R plugs Denso X24ES-U
Dyna-S on one bike, Hondaman on another

[maxheadflow]

Burn time on the scope looks more like points / driver open time.

I'm afraid I don't quite understand what you mean. If you mean to say it looks like just a conventional kettering breakerpoints ignition, I don't see the line oscillate through the 0-axis, do you?

The first picture should be the spark time but I don't see any residual ringing.

The first pic is just a single shot of the rise time, the time the coil is being saturated. Here peak is reached within 25µs.

The second shows the spark as a narrow pulse, tank circuit ringing / decay and dead time.

The second pic shows two complete cycles. I don't know what you mean by 'a narrow pulse'. Burn time, here 2,5ms, is represented in the graph by the elevated line between the initial spike and where the line drops to 0, where the spark duration stops.

This actually brings up an interesting question on Hondaman's ignition.  The the points only seeing 12v, can the gap be closed say down to 0.010" to increase the dwell? Points shouldn't burn at that voltage and get a little more core saturation time at higher RPMs.

Voltage is irrelevant, current is. I don't know about Hondamans, but as far as the control current - if you insist on talking Volts - my breakerpoints see only 6V max. I see no advantage in increasing the dwell. On the contrary, why have the, in my case, 3Ω coils switched on, longer than necessary, waisting energy? For what? With even a standard dwell, measured in Duty Cycle: 52-53%, bike pulls like a rocket well into red zone. Which brings me to: if I must say something nice about an aftermarket EI, it is that simple generic Tytronic, where the designer at least has been smart enough to limit the duty cycle to 50%, whereas Dyna... But 'more' will always sell well in some markets...

I had to go look at some other primary waveforms.  I was assuming that where the voltage sits at 26V on your scope was really open primary voltage. It's not. It is spark time while the field is collapsing. What threw me was the there doesn't seem to be any dead time where the primary winding is sitting at 12V..  From the waveform, it looks like the dwell time is 66%.  Not sure about the RPMs.  At 4000 RPM, should the duration be 15ms between points opening? 60 / 4000?  Points open every rev.

One thing to note, is while current is what is going to burn the points but voltage is relevant as it is was helps to create the arc across the points. It may even extend the duration of the arc.  So it's not irrelevant but I agree, it current that is going to burn the points and not voltage. I expect that it's in the milliamp range and not the amp range in your ignition. 

In your case with lower 3 Ohm resistance primary, I'd expect that extending the dwell time, could be shortened would not be worth it. With 1/2 ohm primaries the dwell time is less than 3 milliseconds from what I can see. Still with a 50% dwell at 9000 rpm, the time would be 3.3 ms.   (1/2 of 6.667 ms )   My discussion about increasing dwell was in reference to running stock coils. There, I'm thinking,  the longer dwell would be beneficial.