My vacuum advance failed and while trying to order a replacement the parts store book list 2 different ones for the V8's. One is rated at 8-11 inches if Hg (73-74 304/360) and one is listed at 5-7 inches (72-74 all V8's).
I'm running a 401 w/a Delco points dist. 9:5 CR and summit 8600 cam. Seems that the 8-11 inches advance would allow the mechanical advance to come in quicker and the 5-7 inch advance would be slower. If I remeber correctly the vacuum advance actually retards timing under high vacuum for easier starting and cruise drivability and then when there is no or little vacuum (WOT, etc) let's the mechanical advance fully advance for more power.
Any advice?