Dinan Iridium Spark Plugs are an excellent upgrade for tuned, and even stock engines, where applicable.* Our spark plugs are made from Iridium - one of the strongest materials available. They last longer than other materials with higher melting points, run cooler, resist preignition, and even require less voltage to produce a strong spark. The iridium electrode with its copper core is harder and stronger than other materials, can dissipate heat more easily, and is better protected from melting, cracking, and other limitations found with standard plugs. Dinan spark plugs are great for high boost, high cylinder pressure, high cylinder temperatures, and high-power situations, and they pair nicely with a set of Dinan ignition coils, where applicable. However, they are not only for tuned and higher output vehicles that may benefit from a plug cooler than the factory heat range – they also are applicable to select non-tuned / stock vehicles as well!* The D640-0002 spark plug applies to the following engines: N20, N54*, N55*, S55, N63/N63TU, & S63/S63TU *N54 & N55 COMPATIBILITY: Dinan plugs are numerous steps colder than stock on both the N54 (3 steps colder) and N55 (2 steps colder) and are suggested for tuned, high boost and/or upgraded turbo applications only. They are *NOT* suggested for non-tuned stock vehicles for these speciific applications. If installed on a stock N54/N55 vehicle the plug will not reach its self cleaning temperature and be unable to burn off the combustion deposits leading to fouling, misfires, and a shorter lifespan of the plug. Compatible OEM Part #Cross Reference: 12120039664, 12120038896 & 12120038704