Spark plugs fitted as original equipment are generally those which represent, for the engine’s manufacturer, the best compromise between cost and quality (Editor’s note: or those who have a technical partnership agreement that has been established). Therefore, if the spark plug used with the engine does not represent the non plus ultra itself, it can be changed without any problems (Editor’s note: unless we are referring to specific single-brand championships in which the make and model of the spark plugs that can be used is established by the regulations and cannot be changed at will), as superior ones can always be found elsewhere in the market place, with improved materials, providing better performance and, of course, they do cost more. Most amateurs and mechanics rely on NGK or DENSO (Editor’s note: to get an overview of the marketplace, we recommend reading this article “Must Have | Kart Spark Plug, which one should you buy?”). The choice of which spark plug to use, and its heat range must be made according to the type of engine and its preparation when tuning the engine.