Need For Manual Spark Advance ?

[marc hildebrant]

Group,

My 1933 Chev. had an automatic spark advance with a fine adjustment at the distributor for different values of fuel octane.

Did Ford use a manual spark advance to save money, or did he use it because the fuels were so poor in the 1920's that it was impossible to develop one advance curve for all types of gas ?

As a side note, is there a book that details "why" Ford designed the model A the way he did ?

Marc