gcc, 68K and ignition advance

[faustini at lamp0.arl.army.mil]

     Here is what little I know about ignition timing.
  
    1) -most- of the work done by the burning gas is done in the first 15-20
        degrees of cranksaft ATDC rotation.I think this is because the piston
        can  "out run" the speed of the flame front. (does this make any 
        sense? what is the typical velocity of the flame front?) 
    2)  I read that it typicaly takes about 1 milisecond for the flame front
        to reach the top of the piston in the average combustion chamber.
    3)  The vaccum advance only advances the timing during part-throttle 
        operatopn, which is why you get significant manifold vaccum. 
        During WOT you typicaly see 1" or less vaccum. Therefore, I conclude
        that during part throttle the cylinders arent "filling" so you can 
        get a little more efficency by starting the burn cycle early. 

        I hope these wild and reclesly gathered facts help.

                                           ---- Lou