There's nothing wrong with dialing in a few more degrees of initial timing advance- - - - -as long as a corresponding amount of centrifugal advance is reduced. For instance, let's start with a distributor for an engine that is supposed to be run with an initial timing of 8 crankshaft degrees before top dead center. That one's probably going to have a centrifugal advance of around 25-27 degrees, and another 10 degrees of vacuum advance, resulting in around 45 degrees of total spark advance at light throttle cruise. As soon as even a slight amount of throttle is applied, the vacuum goes away- - - -leaving around 35 degrees of advance during acceleration. A more radical cam can benefit from added initial advance, so let's dial in an extra 5 degrees of initial, and restrict the travel of the centrifugal advance weights by the same amount. Total timing doesn't change, nor does the advance available during acceleration (IMPORTANT for preventing detonation!)- - - -we've just altered the advance curve a little.
Very few professional mechanics, and virtually no hobbyists have even a basic understanding of how a timing advance curve is calculated. It's a mix of engine speed, load, manifold vacuum, and a considerable amount of "cut and try" using either a dyno or a test drive course so adjustments can be evaluated under identical operating conditions. Wild guesses and anecdotal information just doesn't count!
Jerry
