Originally Posted by Doug M

In the preventive maintenance category, try to get in the habit of looking at the condition of the conical plug after each run. You can spot and eliminate a lot of potential problems by looking at the plug with a magnifying glass. A dry plug with element turning gray equals too lean, not enough oil in the fuel or not enough head clearance. A plug with a lot of oil residue and a bright shiny element equals too rich, this puts a lot of stress on the con rod and rear main bearing. A plug with a distorted element indicates not enough head clearance or a manifold that is too agressive and wants to suck the element out the exhaust. Worst of all a plug with small metal fragments usually means a bearing or rod is coming apart inside.

What you are looking for is a light caramel color build up on the base of the plug without element distortion and a very fine film of oil on the base of the plug. If you have plugs that are black in color, you can lightly sand or file a small area on the base of the plug to the natural color. Be careful to not damage the element when doing this.

To get a good read on the plug, run several laps at race pace, when you feel you have a good tune bring the car into the pits and have your pit person stop the engine within the first 5 seconds. Doing this should give you a good indication of what is going on inside your engine and can save you from major problems in the future.