I have been running W8DC Bosch plugs in my recent rebuild. I am running .045" gap with a CD Unit and Yellow Accel coil. After 4,000 miles, the plugs have a light powdery coating over the surface. (Glad I ran tighter tolerances on ring gaps!) If I did not know any better, the plugs look like they have only a few hundred miles on them.

What kind of life do you people get out of your sparking plugs? I understand each car is different with different conditions. But since most are not using tetraethyl lead any longer is 20,000 miles or more typical?