Why does ignition resistance matter?

Ok so I am looking to update to a dynacoil setup on the x
stock resistance is 10k and i was wondering why it matters.
on Maxim-X.com when he did the update, he said nothing about resistance etc and i just wanted to know what difference it would make if I ran without resisted plugs or plug caps.
i.e. would I hurt anything etc if i ran without? or is my sleep deprived brain missing an elementary detail?

 

Like I know too much resistance would kill the spark strength, but too little? what would that hurt?

 

If you run resistor caps and resistor plugs you will have weak spark and starting issues. If you run non resistor caps and resistor plugs you'll be fine.
Len @ xj4ever has a nice write up about switching over to Dyna coils. He also has adaptor brackets that work nicely also.

 

Easy to over-think this one, resistance inversely effects current in a fixed voltage circuit. Plugs rely on really high voltages to create the arc which ignites the fuel so ultimately voltage is critical to the process.

Running w/o resistance will not harm the motor but it will shorten the duration of the spark and generate higher RF interference which can effect radio's, and TCI's.

Too much resistance will weaken the spark since the amperage will be reduced and the voltage will 'arc' at a slower rate, but it will still fire since the voltage has not been reduced. However tests have shown that in too rich conditions or in any other condition that tend to foul plugs resistance is bad and can lead to failure. Ask any airplane mechanic about this and he will talk your ear off as they have studied this a lot. Fouling plugs at 20,000 feet is MUCHO bad.

Never run R plugs with R caps, but one or the other with functioning coils is safer for your TCI. At lower RPM's resistance plugs have been shown to generate more torque, but at high RPM's non-resistors are better-top fuel guys run super high V and Amperage into their plugs and their radio systems have giant capacitors installed to absorb the RF.

Best performance comes from a potent coil, properly clean & gapped plugs (if required), well insulated wires, and 10k or less resistance. To my knowledge no one has done any comprehensive studies of running a small cc, TCI equipped bike like ours with varying resistances and performance stats-it would be an interesting experiment, but I suspect that anything from 10k to 5k ohms is virtually the same in HP and Torque.

 

In reality, the total energy output of the coil to the plug doesn't change regardless of where the resistance is located----and the resistance could be in the plug WIRES, the plug CAPS, or the PLUGS themselves......or the resistance could be split up between any two or three components.

Different manufacturers of ignition systems, for a variety of purposes, locate the resistance(s) in different places. For example, spark plugs tend to be replaced frequently (at least on older vehicles); and thus whatever (if any) resistance is located in the plug assembly, then that resistive amount also gets "refreshed" fairly frequently. Plug CAPS, on the other hand, get replaced much less frequently........but, as the resistance of those caps change over time (as the resistor degrades in performance), so does the effect of the changed resistor performance. So instead, of, say, being stuck with a 1000-ohm decrease in the level of coil secondary circuit resistance for just 5,000 miles or so (that's how often spark plugs get changed, on average), the same 1000-ohm change in resistance WHEN OCCURING IN THE PLUG CAP, might "hang around" for 20-30-40,000 miles, since plug caps aren't inspected or replaced very frequently.

Same goes for the plug WIRES.........Yamha uses braided stainless steel wire (instead of copper wire, like US vehicle manufacturers typically used) and it's always zero-resistance wire (whereas US mfgs. typically used resistive plug wire). But unlike older US vehciles, where you can/should replace the plug and/or coil wires periodically, the plug WIRES on Yamaha coils are basically non-replaceable, ever.


So, to review: the total secondary coil resistance amount (typically, 5, 10, or 15,000 (K) ohms) COULD be split up among either the plug WIRES, plug CAPS, or the PLUGS. Yamaha choose to have 0-resistance plug WIRES, 5K or 10K ohm resistive CAPS, and for most XJ models, 0-resistance spark PLUGS.

One interesting note is between the 1985 and 1986 XJ700-X models, which used 10K plug CAPS in both model years, but used 0-resistance spark PLUGS in 1985 and 5K ohm resistive PLUGS in 1986. Thus the secondary coil circuit (to each plug) on 1985 models had a total of 10K ohms resistance (plug wires = 0, plug caps = 10K, plugs = 0) while the 1986 models had a total of 15K ohms resistance (plug wires = 0, plug caps = 10K, plugs = 5).


Now, back to the issue of the energy output and resistance. Basically, the energy output of the coil doesn't change, regardless of whether there is resistance in the circuit or not. However, the amount of energy PER UNIT OF TIME will change:

Let's imagine a typical secondary coil circuit which handles a total of 15,000 volts. Now, that 15,000 volts will be discharged across the spark plug gap, inside the cylinder, and makes your fuel/air mixture go BOOM!, but........ HOW LONG does that spark last? Does it happen in a instant flash and then it's gone, or, does it LINGER? Well, it lingers, and it lingers for a good reason...........the longer the spark exists, the better chance that ALL of the fuel/air mixture gets ignited. So maybe it's not so swell of an idea to want all of those 15,000 volts to "exit" thru the plug gap in a flash-bang instant. This is where the resistance plays a factor......it "slows down" the release of those 15,000 volts OVER TIME. So instead of having 15,000 volts/milli-second worth of current flow, let's say we spread out those 15,000 volts over 3 milli-seconds (a "longer" spark duration time). Well, now we'll get 5,000 volts/milli-second over the time of 3 milli-seconds......still a TOTAL amount of 15,000 volts, but reduced in intensity to 5,000 volts but spread of 3 milli-seconds worth of time.

Now of course, there's a certain calculated desired voltage output needed to insure complete fuel/air ignition, under all sorts of engine conditions (idle, off idle, rapid accelleration under light or heavy loads, etc.) and the ignition dudes want to make sure that they provide an amount necessary to perform well under ALL of these conditions, but, also have the desired DURATION of that spark to also make sure that optimize performance.

So maybe 5,000 volts per milli-second of energy, spread out over 3 consecutive milli-seconds of time, is the right combo, and is better than 15,000 volts per milli-second for just 1 milli-second. Or maybe 7,500 volts per milli-second over 2 milli-seconds would be better. Or hey, maybe even 1,000 volts per milli-second for 15 milli-seconds. In all cases, there is 15,000 volts being provided to the plugs, but the amount of resistance in the secondary circuit will determine the RATE (and thus the DURATION) of the energy discharge.


Now, as noted earlier, the 700-X models went from 10K secondary resistance (in 1985) to 15K resistance in 1986, even though the coils (and thus the coil wires), the spark plug caps, and the TCI unit were all the same. So for some reason they felt that they needed more duration (due to the increased secondary circuit total resistance) and were willing to reduce the per-unit of time energy level.

MercuryMan provides the correct answer above, too.

http://www.ultralightnews.com/enginetro ... dplugs.htm

Although the above article references the ignition systems in ultra-light aircraft, the same concepts apply to all ignition

 

Nice explanation chacal!! And that is an interesting article you posted. I guess we were typing at the same time-clearly you type a little faster than I do since yours is so detailed.

My next door neighbor is an airplane mechanic in his golden years (but he's still working) and he has explained more to me than I can possibly keep in my head over the last year. Fascinating to hear how different things are when you work on 'flying' machines-although our bikes fly at times!

I really like hearing about all the redundant systems and new metal-alloy safety features they have put on modern planes-makes me want to ask the staff how old the plane is when I fly

 

i ain't sayen nutin

 

Awesome! thank you guys i felt like it was something that i should know but didn't ive just never questioned it before.
and len, hahaha i purposely posted this on the forum so i wasnt just taking up your time with b*llsh*t questions i always feel bad emailing you dumb questions.