A few questions:
1. What RPM does centrifugal advance take over for the vacuum advance?
Centrifugal advance is set by weights and spring, so this is adjustable. You can check your setup by using a timing light and slowly increase engine rpm, you can see the timing mark starts moving as rpm increase.
You can note at what rpm how much advance is added.
At some point it will stop and the mech advance is at the max setting. (Disconnect vacuum advance when doing this.)
2. If my vacuum advance is on the "ported" side, then it does not advance timing until there is sufficient air going into the carb (and advances more as RPM increases until it hits a stop, correct?
When vacuum advance is connected to the ported line, it does not pull any advance at idle, when the throttle is slowly opened it exposes this port (located above the throttle blade) and only then it will start to advance timing as there is a vacuum in the venturi, depending on the setting/setup of the vacuum can.
Vacuum advance only works when there is vacuum, so it does not increase with rpm, at constant cruising speed it will work, if it runs 2000 or 4000 rpm does not matter, just depends on engine load and the opening of the throttle. So at WOT there is near 0 vacuum and vacuum advance is not working at all.
3. If I recall correctly, when working on cars (back in the day), the vacuum gauge was connected to the port that had vacuum advance attached. If trying to check vacuum from a "ported" point, it will not give me correct vacuum settings at idle, correct?
When working on the engine and you want to check manifold vacuum you need to connect it to the manifold vacuum port, otherwise you can not see the idle vacuum.
4. With no smog devices (except PCV), would it be better to connect vacuum advance to the "manifold" side?
It all depends on the engine and setup, what camshaft, carb, etc. I tried mine on both (440 with 750CFM 4 -barrel) and it does not like manifold vacuum at all.
With ported signal attached to the vacuum can it pings at light loads.
You need to play with it.
If you connect it to manifold vacuum, you might have to lower the initial timing.
For example mine, it likes to idle nice and drive well at 20 deg initial timing (without vacuum advance), with the vacuum canister attached on the manifold port it pulls an additional 10 deg and i am idling at 30 deg initial timing, which is way too much and runs like crap.
If i set it at 10 deg initial timing and use the vacuum can to add the 10 more it will have the same initial timing at idle and will run the same.
When connecting the vacuum can on the ported signal, i can leave the initial timing of 20 deg alone because at idle the vacuum can is not doing anything as there is no vacuum signal present.
Off idle or WOT the story continues, i have 18 deg mech advance which is all in at 2500 rpm.
Combined with the 20 deg initial it will run 38 deg total advance at 2500rpm and up.
If i had set the initial timing at 10 deg as above with the vacuum can attached, and keep the mech advance same, i lose 10 deg of timing at high load and WOT.
Because there is no vacuum, which leaves me with 10 deg initial and 18 deg mech advance, so a total of 28 deg (where without i reached 38 deg).
So at WOT it might not run good at all, but the idle remains good.
I could compensate for this by changing the bushing in the distributor to add 10 deg mech advance, but it will be correct for WOT, but maybe not for cruising and light loads as it pulls too much advance at that stage because vacuum is now also present as the throttle is partially open...so there will be 38 deg total advance and 10-15 deg of vacuum advance which results in 48-53 deg total advance which is too much for my car. (some engines will run with this at cruising speeds though)
So here i could play with the springs, installing stiffer springs will make sure that most of the mech advance comes it at higher rpm while at lower rpm the mech advance is being held back a bit by the stronger springs.
What the mech advance cannot give at this time is added by the vacuum can.
Long story, but just write this out and hope it comes clearer of how it works more or less.
It is trial and error at this stage, each engine runs different with vacuum advance setups.