Re: 1951 288 Vacuum Advance Source

Posted by HH56 On 2022/9/1 12:47:02

I believe Packard mostly used the ported type. The vacuum source is a fitting on the carb where the vacuum comes from a port in the carb located above the throttle plate. When the throttle is closed during idling there is almost no vacuum going to the advance so the timing is not being affected and can be set with the vacuum still connected. On most if not all Packard instructions on setting timing there is no mention of needing to disconnect and plug the vacuum line to the advance.

With the manifold type, vacuum is taken from the intake manifold or the carb somewhere below the throttle plate. When the car is idling and throttle is closed the vacuum is substantial and advance is in full play and affecting whatever setting you made. On those cars the instructions will generally say to disconnect and plug the vacuum before making any adjustments.

Probably doesn't answer your question but there are advantages and disadvantages to both methods and others more into engines will better be able to explain them or there are several hot rod forums that dive into the differences and some reasons for choosing one or the other.