I've been noticing that it's possible to advance my ignition timing an awful lot during high vaccum or part throttle operation before there is a noticable effect in the way the engine runs.
I can't give any specific numbers because I'm not using a distributor machine. But I'm thinking that at cruise, or about 2000rpm and 17" vaccum it will take between 30-40* of advance before it runs bad or stumbles.
How much can I advance my timing for low rpm/ low load conditions, to get the best economy?
Thanks in advance ...

 

try a dial back timing light to figure out your base and total timing, not a distributor machine. 34-38 degrees should be good for most SBCs.