What is your interpretation of these advance springs?
To make sense of why the curves are different its really important to look at the initial timing and rpm for each.
Sticking with the 1968 non-smog and CAP advances, here's what the curves look like on the engine.
The quicker and longer primary advance was to make up for the initial needed for idle to meet early emmisions requirements.
Now, IF for sake of discussion, the two sets of spring were the same as used in '68 for CAP and non-CAP distributors, but used the slots that you have of 11.5 and 13, the advances would be cut off early.
11.5 x 2 = 23* advanced from 5* initial = 28*
13 x 2 = 26*
And if the CAP/electronic distributor was installed for initial at 5* BTDC it would look like this.
IMHO not great to be that much earlier timing except maybe for drag racing - if the max isn't too much. Slant six may tolerate the quicker mid advance but just be careful. Tolerance of the earlier timing for street use will depend alot on the vacuum advance. I put a fair amount of weight in the pre-smog ignition curves for points. The factory spent considerable effort in trying to optimize those things for all conditions.
To make sense of why the curves are different its really important to look at the initial timing and rpm for each.
Sticking with the 1968 non-smog and CAP advances, here's what the curves look like on the engine.
The quicker and longer primary advance was to make up for the initial needed for idle to meet early emmisions requirements.
Now, IF for sake of discussion, the two sets of spring were the same as used in '68 for CAP and non-CAP distributors, but used the slots that you have of 11.5 and 13, the advances would be cut off early.
11.5 x 2 = 23* advanced from 5* initial = 28*
13 x 2 = 26*
And if the CAP/electronic distributor was installed for initial at 5* BTDC it would look like this.
IMHO not great to be that much earlier timing except maybe for drag racing - if the max isn't too much. Slant six may tolerate the quicker mid advance but just be careful. Tolerance of the earlier timing for street use will depend alot on the vacuum advance. I put a fair amount of weight in the pre-smog ignition curves for points. The factory spent considerable effort in trying to optimize those things for all conditions.
