I plan to do an extensive plug wire comparison when I get my hands on a 4-channel scope. Until then here are some basics.
Spark plug wires are just conductors, they can not increase power. Most "high performance" plug wires brag about having low resistance. Low resistance wires will not increase power. In some cases they may actually hurt performance. Most low resistance wires produce electromagnetic interference (EMI) which can interfere with radios, fuel injection and electronic ignitions. If you feel big power gains after putting on low resistance wires it is because your old wires were dead or your coil output is marginal.
Cheap stock replacement resistor wires usually use carbon conductors. They do a great job at suppressing EMI. Carbon conductors work great when they are new but they burn out over time and require routine replacement. High output capacitive discharge (CD) ignitions will drastically reduce the life of carbon conductors. Most street cars don't need anything more than a set of cheap resistor wires.
Solid core wires (a.k.a. copper core, wire core) provide no EMI suppression and should only be used with breaker points or non-computerized electronic ignitions. Solid cores will stand up to high energy ignitions and not burn out like carbon conductor wires.
There are many different spiral core wires made today. They vary greatly from one manufacturer to the next. Generally speaking, spiral core wires suppress EMI better than solid core wires but not as well as carbon conductors. Like solid core wires they can handle high energy ignitions. Many manufacturers coat the spiral core with a carbon compound to aid in EMI suppression. The coating burns out (leaving you with little EMI suppression) so the effective life is no greater than cheap carbon wires. Unlike carbon core wires the conductor doesn't burn out so you don't know when to replace them. The most effective spiral wires have a magnetic core. They are expensive but provide superior EMI suppression and do not burn out. These are your best bet for computer controlled vehicles with high power ignitions. The cheaper spiral conductors (without magnetic cores) work fine on cars without computers.
Spark plug wires could use the greatest conductors in the world and still not work if the insulation isn't up to the task. The insulation needs to keep the spark in and the heat out. Pure silicone rubber is the best insulator but expensive. Most plug wires use a cheap insulator with a thin silicone jacket. These work fine at keeping the electricity in but are more susceptible to heat damage. Some wires don't even use a silicone jacket, don't bother with them. Bigger wires (8.5-10mm) are only needed if you are arcing through smaller ones. Cheap 7-8mm insulation works fine on most street cars. A race motor may need 8.5-10mm silicone insulation because of the extreme heat and high output ignition.
When it comes to plug
wires don't be fooled by flashy advertising, just buy what works for you. I run cheap 7mm
resistor wires on my car with absolutely no trouble.
Questions, comments? Write me, firstname.lastname@example.org