Well, I have seen many talks about this subject in the past...
I have a BBC w/ 12.5 pistons. Cast heads that have alot of port & polish, which I was told by the builder it comes out to 10.2 in the end. I run pump gas occasionally w/ zero problems as long as timing is accomidated too. Sometimes I do 50/50 mix also.
One day, I wanted REALLY find out if my builder was right/accurate. So I did the "Balloon Compression test" using a basic auotomotive balloon that fits over the intake w/ carb removed. Using a remote starter, I turned the motor 1.76 revolutions & the balloon inflated to the erect position... something did not look right.... where it should have had the compression mark for 10.2, it said "Trojan"?? I am still confused...