By the time you get to the point of hearing a detonation rattle the ignition timing is advanced far enough to start doing engine damage- - - -deflected ring lands on the pistons, piston crown damage, etc. There are much more precise ways to determine the optimum advance curve than using a "calibrated ear"- - - - -especially for us old geezers who can't hear thunder anyway. There have been too many jet engines, deer rifles, and racing engine open exhausts in my past!
Jerry
