vacum advance question

Try this...
http://forums.stangnet.com/showthread.php?t=494412&highlight=ported+manifold?+vacuum

Here is a link which has some info about vacuum advance which might help you out http://www.gofastforless.com/ignition/advance.htm but basically there are three kinds of vacuum, manifold,venturi and ported.Manifold vacuum is what is below your throttle blades so it is highest at idle.Ported vacuum comes from a hole just above your throttle blades so it is blocked off at idle but as your throttle blades open up it will be fairly close to manifold vacuum.Venturi vacuum is what opens up the secondaries on a vacuum secondary carb and increases with RPM but since there isn't an external port on a Holley connected to venturi vacuum it is irrelevant but a lot of people get venturi and ported vacuum confused.In order to figure out what connection you have you can either hook a vacuum gauge to each of the vacuum ports or simply put your finger over them while the engine is idling.If you feel suction at idle then it is a manifold vacuum source.Some people prefer hooking their vacuum advance to a manifold vacuum source, some like ported so try both and see what you prefer.