5.7L Ignition Timing Table - Feedback

Why the 'blue dip area' from 900-1200rpm? Why would your engine suddenly like 4.5° less timing at that point?

Presuming you have an auto transmission, to find out what your engine likes best at idle rpm, just put it in Drive, adjust the rpm to what you want, and start playing with the ignition values 'around the active spot' until you get the highest engine vacuum.
Readjust the rpm in between if it changed up.
I think you should be able to get the kPa down well into the 30's

You know that kPa is Engine Load. An idle load of 45 kPa seems fairly high to me, especially at idle when there's hardly any work to be done.
My low cr 318 idles (in Drive) at 500-550rpm with 36 kPa load working with 24° advance (Propane powered+power steering).

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In your table, the advance numbers in mid range (900-2200rpm) seem to be going down, when looking vertically top-down at the columns.
That's reversed of what it should be.
- High load = lower advance
- Low load = higher advance

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Why is your table starting at 200rpm?
That's cranking speed, which you don't need to have in the table.

The rpm-scale in your table doesn't increase with equal steps, making it harder to 'see' smooth transitions.
I would start off with 100rpm lower than your lowest idle speed, say 500rpm, then increase every column with 200rpm, until your reach max torque area of your engine. Then increase with larger increments till redline, as you don't need detailed timing at those rpm-ranges like you want at lower rpms.

My timing table starts at 400rpm, increases 200rpm up until 2000rpm, from which it's increased with 250rpm until 3000, after which the last 4 columns in the table increase with 1000 to 6000rpm (which I'll never reach anyway with my engine).

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When I started playing with the timing map on my Megasquirted 318 I noticed an immediate improvement over the distributor timing curve I had before, which I had tuned and tweaked many times before that.
Everytime I make some noticable changes to the timingtable, I've saved the previous table for comparison. Since I started this, I've saved over 60 timingtables.
Every once in a while when I found that a certain table worked quite good, I put "OK/GOOD" in the table's filename, so I could always grab that table as a known good setup/reference.