Engine snaps after starts?
 

So we redid the ignition timing on our 350 (slightly modified), and set it to about 8 (adv) . The engine ran perfect then so we tried 9 and it began to ping so we put it back to 8 and it pinged... I so we did 7 then 6, both pinged still? Why does it do that? And when I started,my engine, it got going for about ten seconds and then made a large snap and cut off. There was no sign of anything wrong or broken under the hood and it started and drove after that. I any ideas? It's a 1980 if that makes a difference.

I'd be looking at either the distributor, or timing chain/sprockets. Put a timing light on the engine while it's running and see if the mark holds steady. If it wanders all over you probably have a worn timing set.
If it's pretty steady, then look at the distributor to make sure the cap, coil, and mechanical advance all is working as it should.