The motor I currently have in the car is a rebuilt 292 block with '56 272 truck heads.  I don't know anything about the cam or overbore or any other potential modifications.  So, the specs listed in the shop manual are probably not ideal for my engine, though they are perhaps a good starting point. 

I have found information on setting advance curve online, but it is all written with drag racing in mind.  I don't want to race my car; I just want it to work the best it can.  I especially value smooth running, good throttle response, and torque--who doesn't?  But it will probably never see redline in my hands, and the pedal will rarely hit the floor.  Also, I can't afford dyno time.

With all of this in mind, what can I do to find a good advance curve for my engine? 

First: About the specs listed in the shop manual.  It lists a distributor rpm and an advance value in degrees.  BOTH of these figures need to be doubled if I'm using a tach and a timing light to measure the advance in a running motor, right?  As in, if the manual calls for 2 degrees advance at 500 rpm, I would look for 4 degrees of advance at 1000 engine rpm?  If that's so, then I've been doing it wrong--I was doubling rpm but not advance :/

Second:  At what engine rpm do I want to have 26* mechanical advance? 

Third:  What about primary mechanical advance, for low rpms?  Is the factory spec a good guideline for that part of the curve?

Fourth:  What about vacuum advance?  Since it's easier to adjust, is it best to just add as much as possible as soon as possible without pinging? 

Assuming you want to do this without a distributor machine, just on the car, here is a start (assuming you have just a simple timing light without a degree knob.)  First of all you need to clean your harmonic balancer and paint it white where the scale is.  Then you need to extend the degree scale by copying the 0 to 10Deg scale on the Harm bal onto a stiff paper card. Set the zero mark of the card on the ten Deg mark on the balancer and with a Sharpie add on the harm balancer another 10 degrees.  Do this three more times until you have 50 deg total around your harm. Balancer. Darken the 10 20 30 and so on marks so you can tell them from the others marks.

Get the engine to run at whatever idle speed you can achieve, the slower the better with the vacuum advance disconnected.  You could use zero for the timing setting although it might not run at that.  Now with your tach and Timing light note what the distributor gives for advance at idle.  Then starting 1000 RPM and going up to say 4500 RPM in 500 RPM intervals use the timing light to note the actual advance.  You can do all this with the car standing in the garage in neutral.  If you used 6 deg static as a starting setting then subtract 6 deg from each reading.  This will give you the actual centrifugal advance curve for your distributor.  With a modern carb this is the only part of the dist. that provides advance with the carb a wide open throttle.   

While others may have a different opinion, with a stock engine and a 2BBl you probably need something like 40 to 42 Deg total centrifugal advance.  Also Y's seem to like a little more than the 3 or 6 deg static advance specified in the manuals.  Assuming that you want 42 deg and you want to set the initial advance to 10 deg instead of 6 deg you should have something like 32 deg centrifugal advance built into your dist.  It should be all in by 3000 to 3500 RPM.

The vacuum advance adds to the centrifugal advance at part throttle.  At wide open throttle the vacuum signal to the distributor is near zero.  Vacuum advance is harder to measure and dial in.  Basically you need to put a vacuum meter on a tee between the carb and dist.  Then with the car driving on the road you need to listen for knock.  The engine speed should be in the middle of the normal range say about 2500 RPM.  If it knocks note the vacuum reading.  Then working in the vacuum canister, reduce the advance at that particular vaccum reading.  This is trial and error and pretty hard to optomize because the engine must be under load to get it right.  The main problem with just retarding the dist when you get knock under part throttle load is that you also retard the centrifugal advance mechanism which hurts wide open throttle power.

It is really a lot easier to have someone with a distributor machine do all of this.

With regard to vacuum advance adjustment--I have one of the old-type advance units where you unscrew the end and can add or remove washers to alter the spring rate.  I was thinking I could fiddle with those washers until I had as much advance under load without pinging...

and these are the parts................

the fiber tube is at right. The end nut on this unit doesn't have a way to retain shims for the tube - but it isn't an original Ford part either. You could substitute a longer piece of similar tubing in this one. The carbon fiber shaft of a modern hunting arrow comes to mind.....but other materials would work.

I don't have a copy here at the office or I would try to scan it for you.....might be Monday before I could get that done. Send me a PM with an email address if you want a copy and I'll send it to you as an Adobe "PDF" file.

  You asked where to begin on distributor advance curve. I would suggest start by dropping in the new distributor, setting the initial timing to about 10 % BTDC with the vacuum advance pulled and plugged. Then hook up a manifold vacuum gage and at idle out of gear advance the distributor for highest vacuum reading. Back off the advance about 2 inches of vacuum and take it for a spin. Unless you are using a 5 speed and 4.11 rear gears thats really all you need to do. The rest is just to sell Hot Rod magazines to guys. Pete

I have been patiently awaiting an opportunity to put everyone's advice to practice on my car, but the weekend was busy.  This afternoon, though, I'm going to get my distributor adjusted, and I'm looking forward to posting the results!

About the different vacuum modulators--the hex key type should work with my distributor, but a new one is more than 50% of the cost of a replacement distributor, so I'm going to stick with my less simply adjusted unit.  Once the adjustment is made, I don't plan to fiddle with it any more.  As I understand, the non-hex units also have the advantage of being able to adjust total advance in addition to spring rate.

If you've got the engine at idle, and tuned for max vacuum - say 17 inches Hg - then you check initial timing with no vacuum advance. This is then compared with what you get when the full vacuum is applied to the vacuum canister - the difference relates the existing spring preload to the advance travel. Adjusting the spring preload upward reduces the travel - and vice versa - which you knew. But I don't think there is an adjustable "stop" as such in the later canister - except maybe absolute maximum.   

The shimmed version could definitely have an advantage - if you replace the fiber tube with a longer one that limits travel (and you are looking for less).

As for the test drive, there was marked improvement in pickup and power in general, though it wasn't quite night and day.  I didn't hear one bit of spark knock, even accelerating hard up a steep hill, so I guess I could stand to add a little more advance even.  All in all, I'm pretty pleased.  Without having a factory-fresh car to compare it to, I'd say its performance is on par with what I'd expect of this engine/transmission/axle/vehicle combination.

One more thing.  It is very possible that the damper ring on your front pulley has slipped, and the timing is not exactly where you think it is.  Try advancing the distributor then test drive it, advacnce some more, drive, etc. until you notice a ping, then back off until the ping disappears.  If that proves that the timing marks have moved, make a new reference mark on the pulley, not the damper ring.  The pulley won't move, but if the ring has moved once, it may move again.