Classic/Antique Car Repair: setting the timing on chevy 235, octane gas, vacuum advance

Question
Dick...I have a 1957 chevy 2 door wagon I had the original 235 rebuilt to factory specs. I would like to set the timeing, but I get a different answer from every publication I look. I have seen 5 degrees advance at 1000 rpm to 1 degree at 450 rpm I have even been told that you dont need to set it ,"just turn the distributor till it sounds right". Can haveing too much advance damage the engine? when I tried the method of turning the distributor till it sounds good, I ended up with 10 degrees advance at about 900 rpm. It ran good and had good power, but I dont want to damage the engine in any way. What does the factory recomend, and do you need to disconect the steel vacuume lines while setting the timeing?
Thanks, Dave

Answer
Actually, since gasoline has changed so much since these cars were built, setting the timing by "ear" is the preferred method.  My techique is to take the car out on the road and warm it up thoroughly, and then at about 30 MPH in high gear, or in drive if an automatic, accelerate gently and listen for "ping" from the engine.  Set the timing such that you can just barely induce pinging by playing with the throttle under these conditions - that is the optimum setting for the gas octane you have in the car at that time.  If you switch to higher octane gas, you can advance it a bit, but if you hear more than a tiny bit of ping, back it off 'til it goes way.

No, you don't disconnect the vacuum advance while doing this.  I'm betting you are pretty close to optimum at 10 BTC, but you might pick up a little better performance and economy by playing with it as I suggest above.

Dick