Notice even in '66 the CAP engines idle 100 to 150 rpm higher than the standard equipment.
HC and smog reduction methods required less initial advance (sometimes retarded) to put more heat into the cylinder walls, and the loss in power was made up for with high initial rpm. The retarded initial advance was made up for in the distributor with a really fast and longer advance curve. This can become a headache when distributors are swapped around.
