The #85 ran very clean almost no color and showed some black specs on the ceramic. Never heard detonation but I'm sure I was at the initial stages of it. Using #73 they have a tan color, do not foul and no signs of det. Both the 73 and 85 are extended tip plugs unlike the #353 Autolite. For fuel, I run a mix of 92-93 and Torco 104 unleaded about 60% pump 40% Torco most of the time and cr is 9.7:1, 670 heads. Also, with the 73 the ground electrode is heavier than that of a standard plug which will probably make that part of the plug run cooler and is cut back from the center like a racing plug (353) which should expose the flame "kernel" to the mixture better.
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