NGK Iridium Spark Plugs RE7C-L To improve your engine's reliability you may need Iridium spark plugs. They are designed to last longer and operate at higher temperatures than the OE ones and help dissipate heat inside the chambers. This improves combustion and therefore performance whilst making for a more reliable engine by reducing the risk of detonation. If your RX-8 engine is used intensively opt for these NGK RE7C-L Leading spark plugs. The RX-8 engine requires two Leading spark plugs (part numbers RE7C-L or RE8C-L) and two Trailing spark plugs (part number RE9B-T).