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A lot of folks believe that it makes sense to replace the original Platinum or Iridium spark plugs with cheaper copper plugs, and that the only reason that manufacturers use these new expensive plugs is durability. While they are the most durable plugs available, that is not the only reason why they are used.
The real reason why platinum and especially Iridium are used in the electrodes is that these material are extremely resistant to wear in the environment of the combustion chamber, so they can be much thinner; and a thinner electrode is better in 2 ways:
1) the thin wire electrode is also sharper at its tip, and the sharper the tip of an electrode, the less voltage it takes to actually make a spark. This really matters at high loads, where the increased cylinder pressure ups the voltage requirement for a spark to be created.
2) the thinner electrode helps the initial flame (called the flame kernel) develop more rapidly and reliably, because the small flame kernel doesn’t lose as much heat to the electrode. Flame kernel development speed is important for good and consistent combustion, and generally improves efficiency and lowers emissions. Also really helps with cold-starting reliability. Due to the properties of Iridium, thinner electrodes can be made out of it than platinum.If you try to make a thin and sharp sparkplug electrode out of copper it will wear out very quickly. Some folks also point out that copper is superior because it conducts electricity better than platinum or iridium, but this is meaningless for spark plugs. Spark plugs already have resistors built-in to control Electro-magnetic interference, and the resistance of the resistor dwarfs the resistance of the tiny electrodes. The resistivity of the platinum or iridium literally makes absolutely no difference! (understand the difference between resistance and resistivity)
Finally, your ignition system was designed to operate with the thin and sharp electrodes, and your engine was calibrated to operate with the combustion results of fine-wire electrodes, so your engine efficiency and emissions may actually suffer (very slightly) if you switch to cheaper copper plugs. Use an equivalent type to the original in any modern automobile engine.I recently replaced the plugs on my RX400h. It was a V6 and so reaching the 3 plugs in the back was a real pain since I don’t deal with this stuff on the regular.
Is there any other general parts that you recommend to replace with OEM quality parts? I feel like what you can replace it with is also restricted to what’s available at the autopart store.
A lot of folks feel that OEM oil filters are the best quality, but the “premium” oil filters from puroator, Bisch, and Fram are actually usually better quality and filtering efficiency. OEM filters are certainly good-enough, but the specs on the premium filters are better.
For most of the other service items you might buy, major brand aftermarket is usually good quality. This includes brakes and suspension parts like ball-joints. I don’t tend to trust aftermarket gaskets though.
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