The Projection of a Spark Plug
The projection of a spark plug is measured as the distance from the end of the metal shell to the tip of the
A projected spark plug protrudes into the combustion chamber further and provides higher ignitability and improved performance. Simply this can be understood by representing the combustion chamber as a circle. A projected spark plug in effect produces a spark in the middle of the circle (or combustion chamber) allowing for an even flame spread. Conversely, a non-projected spark plug means the flame spread is not even.