Quote: Vacuum in the manifold drops as engine demand increases. If you use ported vacuum you always have a vacuum signal. If you want to make adjustments it can be done using the advance pot on the distributor when you use ported vacuum. By taking vacuum form the manifold you do not have a reliable vacuum constant.
This is not accurate. The only difference between ported and manifold vacuum is at closed or very nearly closed throttle position. Where do you think the vacuum signal comes from? It comes from the manifold.
Then why do you suppose the manufacturer used ported ?
