This off one of the tech sites got me on the higher voltage at plug with more resistance......
Resistor wires are for radio suppression (noise). Resistor plugs raise the voltage necessary to jump the gap, thus raising the amount of energy imparted into the spark itself. With today's alcoholized gas and lean burn engines, you need higher energy to light the charge. Most of today's autos need at least a .040" gap, if not larger.
there IS a drawback to resistor plugs. It raises the voltage to the point that it can cause insulation failure in older coils. Today's coils are built to handle the extra resistance and higher voltage imparted by resistor wire and plugs. Today's auto ignition systems typically make over 60,000 to 100,000 volts!:eek: Most of our old engines made between 10 to 20,000 maximum. Older systems cannot overcome that resistance. Spark (electricity) will find the easiest path to ground. if resistance is too high, it will jump thru the old type shellac used on older mag and battery type coils, thus shorting out the secondary wiring. On some engines, this extra resistance will also short out on distributor caps, and if the resistor wiring is old, it will also break thru the insulation sleeve on the wire itself.
it is NOT recommended to use resistor secondary wiring on magneto fired engines built before the mid 1960s. it also is not recommended for multi-cylinder gas engines built before the early 1960s as the extra voltage built up could arc between distributor posts within the cap. This is especially true in aircraft and v-12 engines, as the posts are close together. With resistor wiring, the potential between posts may be less than the resistance between the post and the plug to be fired, so the spark will jump the air gap between posts and cause a cross fire. Case in point - the American La-France V-12. Using resistor wires will cause cross fire between cap terminals as the spark will jump to a short wire lead to ground rather than a long lead (resistance is greater as distance to end point increases). On the ALF V-12, the high tension leads can be as short as less than 2 feet to as long as nearly 5 feet long, each! With 24 plugs, you can see why resistance is critical. in actuality, there are about 125 feet of high tension wire for 1 engine!. The electricity will always take the shortest path. On the ALF engines, and on our old timers, you must use a wire core wire, like Packard 440 or an equivalent. You should not use modern carbon core resistor wire. Another magneto that is susceptible to resistance damage is the Maytag 72 D and DA. Putting resistor plugs and or resistor wire on them is a sure way to kill the already weak insulation in the coils on these engines. On most of our old engines, it also is not a good idea to pull the high tension wires to stop an engine. if you must pull wires, pull the low tension side ot short the high tension to ground, to stop an engine.
In short - resistor wiring and or plugs raise impedance - the ability for electricity to flow. This raises the voltage necessary to complete the circuit. higher voltage means higher energy at the spark plug gap, thus a hotter spark. Resistance lowers current flow. A special note is also needed here: YOU must not pull high tension wires off autos to test for spark! Too much resistance, such as an open circuit will damage computer controlled ignition systems, and can damage the coil. On older GM High energy systems (HEI), they can build to over 100,000 volts! When it first came out in the late 1960s, dealer mechanics were given notice that the HEI coils could kill you! A cross body shock from an HEI coil would stop your heart, much as an AED used to remedy heart attacks do today. There were several cases of serious injury and death associated with them, as older mechanics, used to pulling off wires, were getting severely shocked by the new system.
