Well, here goes. I've got some experience with wire.
Wire is wire. It'll carry what you ask it to carry, and any inherent
resistance will follow Ohm's law for resistance vs. current vs. voltage
drop. Ohm's law doesn't quit -- you cannot avoid it, so deal with it. High
resistance equates to high impedance which means you may need lots of
voltage to get across the spark plug gap -- so this impedance ends up in
either lower spark voltage or more stray electrical noise. The rest goes to
heat, although the amount of heat generated by the resistance may well
(likely will be!!) lots less than the heat in the engine room. Still, it
turns into heat. Same idea of heating the house or the water or the
ice-melters in the gutter.
Copper doesn't have very much resistance. Carbon-impregnated conductors
will reduce the voltage and help reduce radio interference, which is
strongest at lowest frequencies (that's why you hear spark plug noise on Am
so much more than you do on FM), but their resistance is (relatively) high.
Less electrical noise -- but less spark. Connectors can have some nasty
effects on the conductor -- a funky connection can add a whole bunch of ohms
or a whole bunch of gap, and the resulting spark can play heck with your
radio or your data acquisition system or whatever. Soldered connectors can
help -- but solder can go poor, too, so make sure you've done a proper job
making those connections.
Need to reduce RFI? Use high-resistance wire, and don't worry -- the high
voltage will get through pretty much undiminished and will light the fire in
the cylinder pretty well. Need to have the absolute highest voltage at the
spark plug gap? Use copper wire, and be ready for a ration of noise. Want
to reduce noise some but not do too much to the spark at the gap? Consider
putting resistors on each plug, so that the voltage delivered to the (top of
the) plug is maximised and is reduced only by that resistor. By the way,
something on the order of 20k ohms is likely to be enough, and a
quarter-watt resistor will do the job just fine. Keep in mind how hot the
(physical temperature of the) plug gets and use good resistors.
After all of these considerations are examined you can decide what to run,
but what the heck -- copper conductors don't degrade much with heat, don't
have much loss, and the interference can be considered unimportant if your
other electronics are properly shielded so the noise doesn't play heck with
'em.
Finally -- be patient and come to our pit after your runs. I'll play some
Steppenwolf for both you and me, and anybody else within hearing range.
Jon E. Wennerberg
Seldom Seen Slim Land Speed Racing
#436 M/PS/G 1340 CC
2001: 200.471 mph - 2002 GOAL: 220.554++mph
Marquette, Michigan 49855
(That's Way Up North)
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