Originally Posted By: freshcedar
I get that OEM plugs are best, but what are the engineering reasons? That's what interests me. What makes a copper, silver, gold (do they have gold?), platinum, iridium, etc. plug different from each other? What do racecars use? What are the reasons for a wider or narrower spark gap? Why spend more money on colored spark plug wires? What do performance distributors do better than regular ones? The why is what interests me. Sure, you can never go wrong with OEM plugs, but I guess a little engineering lecture would be interesting, just to satisfy curiosity. At the end of the day, maybe it's boring to some people, and spark plugs are just spark plugs. Fuel economy engineering I find interesting. All the little and big ways car manufacturers are making cars more fuel efficient. But that's another thing.
For instance, this is what one spark plug manufacturer says. Of course, they're biased, but it is interesting:
"What about Iridium Spark Plugs?
Iridium is a super dense material and therefore extremely resistant to wear. That's it!
It is a terrible thermal conductor and a bad electrical conductor, so why would anyone use it to make a spark plug center electrode? Since car manufacturers have to guaranty that their engines stay in-tune for up to 100,000 miles, they can only achieve this with ultra dense Iridium or Platinum.
Nology Silver spark plugs are especially designed for high-performance engines. Silver is the best electrical and thermal conductor of any metal, which makes it the ultimate material for a spark plug's center electrode. The large diameter silver center electrode increases spark carrying ability and spark power. Silver is extremely resistant to erosion, guaranteeing a virtually unchanged electrode gap for the life of the spark plug. Most Nology Silver spark plugs are without a resistor, perfect for performance enthusiasts who demand the most from their engines. For racing or dependability and efficiency for everyday use, Nology Silver spark plugs deliver the most powerful spark."
And they're not legal in CA, which automatically tells you they're awesome, lol. I wonder how they might affect fuel economy. Anyone know?
Finally revealing who you really are (an advertisement agent for Nology)?
Let me give you some engineering reason why silver is not used for spark plug. It wears too fast at the melting point of 962C, even lower than nickel's 1455C, platinum's 1768C, and iridium's 2447C. So, your same design silver plug would probably only last 15k miles when the same nickle steel (aka copper) plug would last 30k.
Thermal conductivity doesn't matter when you are dealing with plugs that have heat range. If it is so good at removing heat you have to reduce the amount of heat it can get out of the plug elsewhere (side electrode, the thread, etc).
Electrical conductivity doesn't matter either when you are dealing with resistance inside the OEM design plug. You rely on that not only to suppress RF noise, but it's also important to restrict the current during ignition to protect the coil (you do not want a current loop to have only 10Ohm resistance of the wire, the current can be so big that it fried the weakest part of the loop which is the ignition coil). When the voltage is high enough to spark, the air gap goes from high resistance to little resistance, it is like shorting a battery's positive to negative, and can put a lot of stress on the coil or wire. The majority of "electrical conductivity" advantage Nology's plug have is due to it being non resistor (hence illegal in California).
Wider center electrode is not to increase current carrying capability. It is to compensate for the low melting point of the silver and it would raise the ignition voltage, making it less likely to spark. The current would be limited by the graphite plug wire, the thin copper wire in ignition coil, the connection contact surface between the wire and plug, the wire and coil / distributor, the air gap between the distributor cap/rotor, etc long before the size of the center electrode or the material.
So, you have a choice of more likely to spark, last longer, less likely to kill your coil plug (platinum, iridium with resistor) or a less likely to spark, last shorter, and more likely to kill your coil plug (silver without resistor), which one to choose? The answer is obvious.
p.s. if silver is so good why would OEM use the more expensive platinum and iridium?
