Compression/Octane

[Steve Robertson]

I just measured the compression ratio of my motor and after a few screw-ups
(clarified thanks to Z) I'm fairly confident that the compression is 12.5:1. 
For
those of you running a similar number is 100 octane enough to avoid 
detonation
or would a few more points be needed? If it makes any difference the heads 
have
not been milled and I am running a full three layer head gasket.

thanks,
Steve