An up-to-date spark plug must be individually tailored to the different engine designs and driving conditions. Therefore there cannot be a spark plug which functions without any difficulty in all engines.
Since the temperature development in the respective combustion chambers in different engines varies, spark plugs with different heat ratings are needed. This heat rating is expressed by the so-called heat rating number. These heat ratings represent an average temperature measured at electrodes and insulators, corresponding to the engine load in each case.
- The optimal temperature window: Spark plugs require a special temperature window in order to work optimally.
- The heat rating: A spark plug must release a precisely defined measure of heat to the cylinder head. Only in this way can the optimal temperature window be adhered to.
- Heat dissipation and heat flow: Nearly 60 % of the heat dissipation takes place through the spark plug case and thread.