NGK Iridium Spark Plugs RE8C-L When tuning an engine you may need colder 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 modified or used intensively opt for these NGK RE8C-L Leading spark plugs (one grade colder than OEM). 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).