Hi Folks.. Most of these vacuum advances I have seen have a 3/32 (?) allen screw down inside the hose nipple, so you can actually modify the point where the advance comes in. You wont be able to alter the amount of advance with this, but you can adjust the screw and hence, the point where the advance begins this way. I have been able to run with the vacuum advance coming off of the manifold vacuum this way, with no ping or other ill effects. That was not the point, just originally to say that I know that the NAPA and Crane and many others that are out there have the adjustment. Ill save the pros and cons of manifold versus ported vacuum and the discussions of rate of advance and all the rest for another day! take care, Mikey 62 Crown Coupe