Originally Posted By: deeter16317
I thought I remembered reading that while they last longer, copper plugs actually have more spark energy? Those precious metals don't actually conduct that well.
I have read on the Subaru forums that guys who actually rally cross run copper for that reason, with a more frequent change interval.
K, perhaps you or the other posters misunderstood the notions of copper (especially copper resistor plugs)plugs: copper plugs does not mean that the entire plug, from the spark plug boot end all the way to the tip are made of copper (firing tip electrode and ground electrode are made of nickel alloy for wear/erosion resistance) but only sections of the electrical conducting core inside composed of copper alloy. Copper has the characteristics of heat dissipation and when done properly, should go along with the ceramic stem nicely as far as gas sealing and thermal expansion property's concerned. In other words: the tip is not made of copper alloy(won't be) for corrosion/erosion resistance and durability.
resistor inside spark plugs have been mainstream since the 60s and onwards and main purpose is for radio noise suppression (RFI suppression). Under high voltage (high tension) situation, the resistor poses little to no effect to the overall spark energy (or the voltage it takes to cause the ionisation of gas on the sparking electrode tips before spark jumps the electrode) at all. The only time you'll feel the impact on resistor/non-resistor would be on an non-electronic sparking system (e.g. point type) and/or having poor/inconsistent high voltage generation issues.
Lastly: with modern stringent emissions systems and control, it is against modern motorist's favour to have a low-tech, unreliable sparking systems (point type HV systems, copper plugs, etc.) for the modern ODB-II systems are very sophisicated and intolerant to poor/inconsistent ignition systems. Copper plugs are good for typically no more than 20,000miles (standard ignition systems only; "waste spark" type not applicable for the erosion on electrode tips are magnitudes quicker) before they start to exhibit significant deterioration in performance and firing consistency, which will trigger all kinds of CEL codes or even damage emissions components and monitoring devices downstream.
This is the reason why manufacturers resort to using at least Platinum (better erosion resistance than copper, sub-par to that of iridium) as standard equipment these days.
Since major spark plug manufacturers differs in manufacturing methodology, etc. even between different materials (e.g. copper, iridium, platinum, etc.) due to different thermal expansion rate in these metals and also from a gas sealing and fusing to ceramic body standpoint), and also different firing voltage requirments and heat ranges, etc. casualy changing any engines that use iridium/platinum as standard (per engine design by car manufacturers) to copper plugs and claimed performance gain is, IMHO, deemed ignorant, if not reckless.
My 2cent's worth.
Q.
p.s. modern solid-state ignition systems are capable of generating in excess of 10kV easily, and sparks strong enough to jump a gap of over 1" consistently. Anyone whose taking on the observation of the difference in firing voltage between copper vs precious metals such as platinum, iridium, etc. to have an observable impact on modern EFI (particulary OBD-II systems) engined cars should think again.
