a while back a post was done and i think someone (JP?) stated to try reducing the timing at 400/600/800/1000/1200/all map. this i believe was in response to a stumble issue. i recently discovered i had way way too much pumpshot in my AE tables so took out 50% or greater AE and seems to like it. first drive today on AE adjustment. BUT my Q is the timing! i also took SA tables to above. idles about the same? seems timing was not the stumble issue but that is what i have in tune today(SA). my prior SA tables(and others i see) had way more SA in those area's. i wanna say 20's?

why does an engine need more SA than 4-12 at those rpms ?

the combustion event need not occur at 20 deg A if at idle? does not the combustion event need to occur at TDC? would not 20 deg cause it to occur too early? what does a carbed car idle at? 6 deg right? does a traditional dist raise SA somewhat linear(weights)? i mean all SA is in by RPM where max TQ occurs(then pulled back w vac)? if so i would bring in 36 deg just b4 my max VE in fuel tables. right? then trail it down beyond that to the SA i see in stock GM table i have saved. fee free to correct any misstatement.
ps. not trying to optimize SA tables just get them improved a bit.

OK. I am a little confused about your question(s), but here goes.

Yes many people have around 20* or so in there SA tables. Carb's usually will run anything from 5-25* advance. Depends on what the engine wants. A vacuum advance car may have 6* initial advance but then it will have say 18* with the vacuum advance.

When I had my old 350 HSR running on MegaSquirt I had around 23* advance at idle with a vacuum advance dizzy. In my 305 TPI I had around 18-19* at idle. You want more than 0* advance at idle because it allows for combustion to build more pressure and finish expanding (burning) as it gets to TDC. The burn is not an instantaneous reaction to a spark. It will take a little amount of time. So giving it a small amount of spark advance will help it to build pressure up and exert more force on the downward stroke.

Think of it like turning a car. You don't start to make a turn when your car is exactly in the middle of the intersection at a 90* angle with it.

The old style dizzys did have timing in a linear curve. It should usually all be in around 3,000 RPM. That can change though. that is why you can change weights and such. And not all engines want 36* timing at WOT either.

yes i am aware the combustion takes some time. i guess that was my question. at 800 rpm/ idle would not the begining and end of event be well before piston hits TDC? would not 8 deg adv be a better choice than say 20 d adv? i can see how at higher rpms we need more lead time(advance) than at idle. after all 3200 rpms is 4X faster piston speed than is 800. not that you want 4X greater timing. agin feel free to correct me on this.

I understand your point now. The only thing I could say to that is that I would always tune for the lowest MAP reading within reason. The lowest MAP reading will net the best mileage and power combo. Give it whatever it wants to make it