Posted by chriscase on Tuesday, February 15, 2005 at 12:31PM :
In Reply to: 230 Distributor Question posted by Brett in AK on Tuesday, February 15, 2005 at 8:12AM :
Under light throttle there is a smaller charge in the cylinders, permitting more advance without pinging. But under full throttle with a maximum air/fuel charge, that much advance would detonate/ping, which would be detrimental to both fuel mieage and engine life. So, they came up with the vacuum advance distributor. It controls the amount of advance by sensing throttle usage via intake vacuum, thus gaining maximum advance for the load at that time. You will get better gas milage and smooother accelleration with a vacuum distributor. The only 'modern' engines that use a srict centrifugal distributor are the ones run at constant load- marine use where you never go downhill, or industrial use where the load is known. These old flat heads need all the efficiency you can afford.