On a series of chassis dyno tests of the family race car back in the mid-1950's, we found that once maximum HP was reached by advancing the timing, one degree more timing killed as much power as retarding the timing 4 to 5 degrees. If you're unsure of where the max power point is, less is always preferred to more advance! We've observed the same basic trend on alcohol-fueled flathead Ford engines, NASCAR-specification small block Chevvies, Big-block Chrysler tractor pull engines, and various bone-stock street machines. Too much timing advance destroys horsepower and engine parts!
Jerry
