Does anyone have an idea what the advance curve for a propane-powered 307 SBC should be?

Found a big tank for the truck?

Different truck... the Ford's a 444 Diesel, this one's a 307 Propane GMC.

All I can tell you is that we used the stock HEI timing curve in my 1979 Impala 350. It worked quite well.

However, if I recall correctly, the advance can be quickened somewhat. Propane has a higher octane rating, so try one step looser on the springs and then advance the timing until it pings, then retard it 2 degrees.

If that works well try the next set of looser springs, etc.

Just make sure the coil is a hot one. More octane equals harder to spark. I remember the day we converted mine over. Two plugs and two wires that worked fine on gas gave up the ghost instantly on propane

Yeah that's what I hear, propane is around 110 octane or so. I've got access to a good old fashioned distributor machine here too, so it's fun to play with timing.

The nicest thing, IMHO, is that propane costs half what gas does and still gives you almost 90% of the mpg

I remember buying propane for .08 cents/gallon.

That was 20 gallons at 8 cents = $1.60 to fill the tank :hail:

For you Americans out there, that would be like filling your 20 gallon tank for $1.00 ... pretty hard to take, eh?