HP question.....

this is a little off topic.. 454 chevy i'm working on for a guy...
its a 9.5:1 compression motor... Big cam, ported heads, stock lower end...

He wants to change the pistons and get 12:1 compression to work with his heads and cam...

What kind of power could you see gaining from just a compression change.??? I know its not a lot of info.. But..i'm looking to know if its like 10 hp or could it be 75 hp gain... I do have more info if its needed... Thanks...

A lot depend on the other parts, but its not out of line to expect 10 to 15%, so a 450hp motor could hit 500 or thereabouts.

Also your going to need race fuel any way, so just bump as much as practical.