Why does advancing ignition give extra power?

[A900ss]

In simplistic terms, why does ignition advance give more power?

I don't want to know about detonation and ignition retard(yet), just why ignition advance gives more power.

Thanks

[A900ss]

mcford said:

You want the greatest gas expansion when the piston is at the top of it's travel, as combustion takes a little time it needs to be initiated just prior to the piston being at top dead centre, hence the ignition advance.

Too much advance and the gas expansion will try to push the piston down while the crank is pushing it up, too little advance or retarding the ignition will push the piston down as the crank is pulling it down which will reduce the force of the gas expansion.

Thanks - makes perfect sense. So the faster the engine is spinning, the more advance needed I guess?