CIS and timing experts: Total advance connection at TB and total advance possible.
 

The vac advance is supposed to be above the butterfly (In front of the TB) and the retard on '80-'83 below the butterfly) Rear of TB).
Is this correct?
Even at 850 RPM, there is strong suction above the butterfly on the advance line pulling the full ~5 deg in idle.

Some thoughts:
Porsche states to set timing at 5deg with vac disconnected for SC's.
That would mean that Porsche recognized the effect of the vacuum even at idle???

More observations:
I retarded the timing to a total of 29-30 max. vac connected which leaves the timing at 8-9 deg in idle with vac re-connected.
(If I set it 30-32, it'll be 10-11 deg vac connected)

At this point, I wonder about the total advance possible with the SC-distributors?
I have 3 distributors to play with: '78, '80 and '82.
They appear to perform the same.

Any thoughts?