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I posted this on another site that made it a sticky for those of us who can't remember where we were at yesterday much less what our engine is telling us in detail ! I can't remember where I got this but once again " Thanks Dude ".
Plugs can only be correctly read when the car has been shut down immediately at the end of a run without driving it back to the pits. Get off the track and coast to a place you are safely out of the way and either read the plug there or change one with one you have in your pocket so you can read it when back in the pits. It may take a couple of runs to get the correct color.
The porcelain around the center electrode is divided into three main area for reading. The third that is closest to the tip is reflective of the idle and transition circuits and is of no concern to a racer. The middle thirds is only colored when you drive down a road at around 30-40 mph and normally reflects the primary jets with the power valve closed. The part you are interested in is that third all the way up inside the plug where the sun don't shine. It will take a magnifying plug reading flashlight or to hold the plug so the sun will shine up inside. Normally aspirated cars should read a light gray or tan ring all the way up inside with the color depending on type of fuel. Most fuels will be light gray/tan. For nitrous cars it will normally just be a faint gray coloring or just turned completely white (off white maybe).
The ignition timing can be checked by looking at the color of the ground strap and looking for the blue line on the ground strap which is really the annealing point of the metal. If you are using a gold colored ground strap like with an NGK then not enough timing will show the ground strap as still gold or going light gray. As you advance the ignition and put heat in the plug the strap will turn darker gray as well as the metal at the end of the threaded area. When it turns medium to dark gray you start looking for the blue line (band) around the ground strap. You want this blue line to be where the ground strap makes the 90 degree bend. If you go too far the strap will pick up rainbow colors and the next step beyond that is to start melting the strap. When you are close then only change the timing by one degree at a time. Also remember that 10 degrees air temp change is the same as changing the timing by one degree. So at night when it has cooled down you can add some timing. If your ignition has the capability of adjusting the timing of each cylinder independently then you can use that feature to have the blue line in the same position on all the plugs.
The round flat area of the plug at the end the threads should be dark gray or flat black and should not be sooty. If it is sooty then it can mean that your plug has not been tightened enough and you are sucking fuel and air past the threads of the plug.
If the car has been run rich then it is possible to glaze the plugs during a run. This glazing appears to be a glossing coating of the porcelain with a color of greenish yellow or brown. This glazing will cause the plug to short out and misfire and raise ring lands or pop through the exhaust when going down the track.
If you hold the plug in the sun and you see what appears to be small diamonds on the porcelain then you have detonation and need to add fuel and/or take out timing.
This does not apply for Alcohol..and opinions may vary!
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ASK NOT WHAT DRAG RACING CAN SPEND ON YOU, BUT WHAT CAN YOU SPEND ON DRAG RACING !
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