As previously explained the Automotive industry believed that by maintaining the air / fuel ratio of 14.7:1 by electronic means they had already controlled the emission levels, because they assumed that the spark plugs used were the correct ones. No One Was Aware that although the Air / Fuel Ratio Was Correct, the Polluting Emissions could Dangerously Increase if the Spark Plugs Used were Not the Right Ones.

Neither did the Automotive industry think that anyone could make an error when choosing spark plugs since these were advised by manufacturers through Spark Plugs catalogs in the "Application Tables" section, where one can find the correct spark plug to use according to the type, brand, model and year of the vehicle.

Nevertheless, there are some determining conditions that arise in the life of a vehicle, that make the information in the Sparkplugs catalogs no longer universally applicable.

The point is that the sparkplugs of the ignition, apart from taking the spark to the inside of the Combustion chamber of the engine to light the mixture of air and gasoline; have a very important function: to regulate the temperature inside the Combustion Chamber (between 400ºC and 850ºC). This is why there is a great variety of sparkplugs with different Heat Ranges designed to work for different types of engines of different types and models of vehicles. This is called the Heat Ran ge of Sparkplugs. There are cold sparkplugs, hot sparkplugs, as well as spark plugs of all the intermediate Heat Ranges. SOURCE: (*) Autolite Spark Plugs / Allied Signal Inc / USA. Champion Spark plugs / Federal Mogul Corporation / USA. Chilton Repair Manual and Tune Up Guide / USA.