compression ratios of typical single piston engines

[Plasmech]

I fully understand that the more octane (or lead to an extent) a fuel has, the more resistant to pre-det it has. That's pretty common household knowledge.

I guess what I need to understand now is why aero engines need so much spark advance (?)

edit:

I think the fuel is leaded to prevent damage to the valve components in engines of old design, rather than to prevent detonation.

ahhh...forgot about that. Good point!