Thanks Oddjob
Did some forum search on DR7EA vs D7EA and found some discussion on same subject. It states that DR7EA will work but life will be half compared to D7EA. The very fact you noted since these are R resistance packed 5ohms once these build more resistance, will demand/ need more power that coils will be unable to deliver.
No no, this is far from true. The resistors in both the R plugs and the caps are wired in series within the coil output circuit. As such, they can only reduce the current flowing through the circuit. This would be LESS power. They would only use more power if they were wired in parallel. They are not.
For the purposes of discussion, Ohm's law is I = E/R. Since the voltage at the spark plug is determined by the spark gap distance and the atmosphere within that gap, it is effectively constant for a specific engine when considering current flow effects of resistance instances.
Resistance is additive in series circuits.
In parallel circuits. The formula is 1/Rt = 1/R1 + 1/R2 + 1/R3 +...
Rt = R (t)otal
two 5K resistors in series = 10K total.
two 5K resistor in parallel = 2.5K resistance total.
Plug these resistances into the ohm's law formula, and for the same voltage, you can only change the current. The lower the resistance, the higher the current.
Say the spark voltage is 10KV. There are two spark plug leads with 10 KΩ in each leg of the series circuit, which equals 20KΩ total (excluding the coil windings, for the purpose of this excercise). 10000/20000 = 0.5 A
If we use 5K caps and standard plugs the total resistance is only 10KΩ. Use the same formula, ohm's law, we still have the same spark gap voltage 10000V / 10000Ω = 1.0 Amps. Twice the current.
So, as the ignition circuit resistors are in series, they reduce the rate of discharge from the coil as well as the current that can flow through the spark gap, as the coils are charged to the same potential between each spark event. This would EXTEND the plug life by reducing electrode erosion and make the spark event longer because it now takes longer to drain of the energy stored in the coils.
The only detriment to more resistance is that as the plugs age, they demand more voltage to create and maintain the spark electrode plasma channel. This is mostly because the sharp edges of the electrodes round off and there is no longer a defined point to leap from/to. You can extend the life of standard plugs by filing the electrodes to recreate the sharp edges of a new plug.
Anyway, too much added resistance can make a marginal plug, coupled with low system voltages, slightly more difficult to create and sustain the spark plasma channel across the electrodes. Otherwise, run time operation differences will be largely unnoticeable.
FYI the spark plug resistors are nominal 5000Ω or 5KΩ. If you use them with the 5KΩ plug caps available today, it results in the same 10KΩ lead resistance that was delivered from the factory by Honda on the North American continent.
When my 10 KΩ plug caps finally break down, I'll switch my CB550s to using R type plugs with the 5K plug caps (if I can't find 10K caps).
Cheers,
