RB,
Post #90.
Smart people give their engine the idle timing it wants, which can be as much as 50*.
You only have to read this forum & others where people have advanced their idle timing & found the engine idled higher, smoother etc. It idled higher because the engine was making more HP from the extra timing; the smoother idle should be self explanatory....
I have just given you the production specs for my GTO in post #94, for a production engine, 10.75: 1 CR, intake cam duration under 200* @ 050.
Engines with longer duration cams produce less compression pressure at idle & have more exh gas dilution. The lower compression takes longer to burn & the exh gas dilution also slows the burn rate. Both require more ign timing at idle. Not rocket science.
The 26* of factory idle timing that my GTO had is a conservative number, as manufacturers have to cater for the worst case operating conditions.