Right, because it's true for Chebby double-hump/triangle closed chamber heads, BTDT.
If You generate maximum manny vacuum with the timing, it will barely idle at an acceptable speed(high) & will run hot whether You like it or not. Didn't believe it Myself, working on a '66 Chevelle, but that's exactly what happens...total power timing was right on & no detonation but had to back the base timing down from 12° to 7° IIRC.
