Which is better and what are the advantages. I've got a 850 DB and not sure which way to go for my distributor vacuum advance hose.

At anything off idle, the ported vacuum and manifold vacuum are the same. Only at idle are they different, no vacuum for ported, and full vacuum for manifold.

My mild small blocks have always liked manifold vacuum better. It helps clean up the idle, and allows me to turn down the idle screw and close the blades.

Some rowdier engines with automatics might work better with ported. With manifold vacuum, there is a drop in idle rpm in gear, and a subsequent loss of some vacuum, so these engines lose even more idle rpm in gear, and then idle too high in park. Ported vacuum will help keep the neutral and in-gear idle closer together.

Try it both ways, and see what your combo likes better. smile.gif

Chris