Quote: Ported vacumn is generated by flow velocity thru the venturi of the carb.
That is correct. And intake manifold vacum will be right around o at wide open throttle where ported vacum will be high. Thats why ported is used so much as it will give more advance with more throttle. . Ron
Again, this is wrong information. At wide open throttle regardless if it is ported or manifold vacuum there will be no vacuum or very little vacuum. The ported vacuum is there for just idle or very close to idle conditions. Once you are on the road there is very little difference between the two. I still think that using ported vacuum is better for more situation as long as the distributor advance slots have been shortened to allow much more mechanical advance then is the norm on the stock dist.
The ONLY difference between "ported" and manifold is the ported passage is just above the throttle blades. When the throttle is closed it closes the port = no vacuum = no vacuum advance at idle. As soon as you crack the throttle past the port it then sees manifold vacuum. This was an emissions era invention.
The manifold vacuum port passage is below the blades so it sees vacuum or the lack of it all the time.
A simple test to confirm this is get 2 vacuum gauges and hook one to each port. You will find that they will be basically the same everywhere but idle.
