whoever told you that was referring to the heat range of your spark plugs. If you are running nitrous, typically you need to run plugs with a colder heat range to avoid severe detonation and killing your engine. Now if you put colder ones in with the nitrous, and they are too far on the cold side I could see you needing to bump up a range, but that's it. A plug with a stock heat range would be like an Autolite 25. Usually the heat range is indicated in the part number of the plug, but it depends on the brand and how they do their part numbers.