These plugs are heat rating 7 which is 1 step colder than the stock plug. This is good for modified engines and can help prevent detonation or pre-ignition caused when the spark plug tip gets hot- causing a 'hotspot'. Colder plugs transmit heat away from the plug tip faster to avoid this. For more mildly tuned engines we also stock NGK 8 & 9 rated racing plugs. We have a large and rapidly expanding range of items for the Skyline- consumeables, performance upgrades, tuning items, as well as a wide range of suspension and steering parts- Wheels, wheel bearings, strut bars, camber arms, & performance uprated bushes. Please check out the other items in our shop for brakes, water pumps, spark plugs, filters, fuel pumps, and lots of other essential parts. Check out our other items for great tuni.