Ignition timing question

[Barry Tisdale <btisdale@cybersol.com>]

I was going through some of my *old* engine stuff & came on some
distributor curves once set on a '65 SBC.

The timing was around 15° static, centrifugal max about 25°, starting @
1000 (engine) RPM, maxed @ 3000 RPM (total = 40°).  Vacuum advance would
add another 12° or so at low engine loads.

Studied some timing specs for various Syclone (7749 ECU) chips just now -
*radical* differences!  Overall timing looks to be about *half* what the
old dizzy specs were. 

Assume the normally aspirated section of the Advance vs. MAP & RPM table,
i.e., ignore values above 1 bar.  Timing maxed at 3200 RPMs at about
16-17°; around 20° max added for light load conditions.  Naturally, retard
needed under boost, but the NA part of the table is real different from
what I'd expect.

Seems to me *lots* of timing could be added at cruise & light load (light
for a turbo) conditions - am I missing something here?  Are these big
differences for emissions reasons?

Thanks for any clarification -

Puzzled - Barry - Sy#26

Timing looks to be about half what the old distributor curves were