Kind of new to RC Nitro but I know in turbo cars (like my Eclipse) you run colder plugs because the compressed air from the turbo is hotter than uncompressed air. So you need a colder plug that will resist heat better. If you run a colder plug in a car that's not turbo charged, it will not run as well because the temperature range where that plug operates the best, is not being reached. Hope that helps.
Flash