Is that where they start to move, or is that all-in at 5"?
I'd like to point out that the range of advance
degrees is set by the stop on the arm, and the only way to change that is by fabricating a new stop such as you mentioned... what
may be adjusted is the start of the advance (from just beginning to move, to all-in). If you screw the adjustment CCW and the start changes from 6" to 8", the all-in vac will also be pretty close to 2" higher also. But it will be the same number of degrees stamped on the arm...
That said, I've been running manifold vacuum for a while, partially because my 950 doesn't have ported vac! :D But it's a good match for my
[email protected] cam (as described in my thread in the Mopar Perf forum). It has about 8.5" at a 1200 rpm idle, which does not pull the can in all the way even at full CW adjustment (it starts to move around 5-6" but takes 11" for full 16 crank deg advance). The idle is quite stable at 34 deg (mechanical is 24, so the can is about halfway in). So far, no ping. :)
