Reply to "Vacuum advance, ported or manifold, age old question answered"

There are statements in that article that are 100% erroneous. Engineer or not, his approach is too simplistic.

Either type of vacuum advance can be used if the static advance and centrifugal advance are set-up properly to account for the differences between the two methods. However, ported vacuum works better in some applications, and manifold vacuum works better in others.

I've covered this topic in the ignition section of the Engine Building Advice sticky.

I think part of the problem is that some people don't have a good idea of how ported vacuum and manifold vacuum differ from one another. There's this drawing of a carburetor with vacuum gages attached to both the ported vacuum connection and the manifold vacuum connection. The carburetor is shown in 5 pictures at idle, 25% throttle position, 50% throttle position, 75% throttle position and wide open. Its a good aid in helping folks understand the differences, the problem is I've seen the picture a hundred times, but I have a stack of technical books 6 feet high, and for the life of me I can't find which book had that picture in it. Very frustrating. If I find it I'll post it.

-G