Patent ID: 8350456

Claim:
A spark plug, comprising: an outer metal shell, the outer metal shell having a distal end that defines a recessed opening; a ground electrode tip extending from the distal end; an insulator located within the outer metal shell, the insulator having a distal end extending past the distal end of the outer metal shell; an electrode tip located on the distal end of the insulator, the electrode tip being located in a facing spaced relationship with regard to the ground electrode; wherein the insulator has a substantially straight portion that extends from the distal end of the insulator into the recessed opening of the outer metal shell such that no portion of the substantially straight portion contacts the outer metal shell and a portion of the substantially straight portion extends into and out of the recessed opening; wherein the insulator further comprises a tapered portion configured to increase the diameter of the insulator, the tapered portion being completely received within the outer metal shell and extends from the substantially straight portion; wherein an overall length of the substantially straight portion (X) is a function of i) a portion of the substantially straight portion not located within the outer metal shell and extending from the distal end of the outer metal shell (S) and wherein X is defined by the following formula X=C1*(T−S*C2) and C1 is 0.25 and C2 is 1; and ii) a combined length (T) of the substantially straight portion and the tapered portion; and wherein T is in a range defined by a lower limit of approximately 0.050 inches and an upper limit of approximately 1.000 inches (1.27-25.4 mm) and wherein S is in a range defined by a lower limit of approximately 0.00 inches and an upper limit of approximately 0.200 inches (0.0-5.08 mm).