I have a new set of NGK Iridium plugs that I picked up cheap a while back.
Noticed that the tips are really tiny vs. the regular NGKs. Mike, do you happen to know what advantage (if any) to them is. Hotter spark maybe?
Which would result in what? Or maybe they're just a gimmick.
From my experience, NGKs are the most reliable spark plugs for any kind of motor.
The primary advantage of precious metal spark plugs is the melting temperature of the metals used. This takes advantage of a basic property of spark propogation, which is for a given amount of energy delivered to the plug, the smaller the electrode area, the greater the intensity of the spark. Having seen high speed films of tests done to find out why this is so, it is revealing to see the spark jumping away from a wide plain steel electrode -- it actually leaves the electrode over the entire tip then "bundles", or tries to form into a single narrow column before hitting the ground electrode. In this, it is only partially successful as the ground also has a fairly large area and does not present a single narrow target -- you end up with a series of small sparks twisting around and interfering with each other. With a narrow electrode, the spark jumps already bundled, so does not produce multiple paths. While it is possible to sharpen a steel electrode tip to a point, it would not last very long due to the relatively small area of the tip melting a tiny amount every time a spark jumps, eventually becoming a large ball considerably further away from the ground. With precious metal electrodes, which melt at a much higher temperature than steel, the spark doesn't heat the metal to its melting point, so they not only last considerably longer, they also maintain good spark intensity for practically their entire lives. The best plugs of this type have precious metal tips on both center and ground electrodes, making them practically eternal. As for the differences between NGK and Denso, it's strictly a matter of personal preference rather than any major advantages given similar construction. In my case, NGK gets the nod in most situations.
Rob
