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If you reduce energy in the primary of a coil, you reduce energy on the output of the coil. Power in = Power Out. You put in less voltage and more current and effectively convert that to higher voltage and less current on the secondary so power is equal other than efficiency losses. Now, I do not know how much overhead is built into the coils circuitry (aka if it is regulating it, etc).
But when the ECU applies voltage and current to the primary side, it will build a strong magnetic field. That power is removed and that causes the field to collapse which induces a very high voltage in the secondary. If adding resistance to the primary and not changing anything else I believe it will cause a weaker field and thus, a weaker spark on the secondary side.
Adding resistance to the primary side can help to increase life of the coil but the rest of the system must be designed to work with the increased resistance.
I would say depends on what the system its connected to is designed for. Obviously the 06+ is designed to run with the higher resistance to produce the same spark energy. I have no idea what happens if you put the higher resistance coil in an early model or a lower resistance coil in the later models. The latter would be drawing more current from the system. But we dont have the internal schematic for the ECU or the coilpacks so it is hard to speculate how it would work or what issue it can cause.
So maybe, per my lengthy speculation post, Honda indeed added resistance to 06-09 coils, for rfi interference with XM radio (and changed them for all markets, even if no XM, just so same parts everywhere).
Maybe, as part of that, they went from 980 ohms to 1250. So that would mean using newer 1250 coils on older cars = weaker, bad idea. But old coils newer cars, nbd if you don't have XM.
So maybe NGK knows this, so to keep their costs down, they just make coils per the older 980 spec, and say they work on all S. That will work perfectly in marketd that don't have XM. In markets that do, still fine except if car actually has XM, but since so rare, not something they care about enough to make coils with 1250 resistors.
Note that the OHM values wich i posted are meassured on aftermarket Coils. It would be helpfull if some other members start meassuring to.
I would say depends on what the system its connected to is designed for. Obviously the 06+ is designed to run with the higher resistance to produce the same spark energy. I have no idea what happens if you put the higher resistance coil in an early model or a lower resistance coil in the later models. The latter would be drawing more current from the system. But we dont have the internal schematic for the ECU or the coilpacks so it is hard to speculate how it would work or what issue it can cause.
My thought was that in a earlier 00-05 Modell coils with low(er) OHM maybe give a better spark. Maybe. Or at least dont have any adverse effect.
