I didn't build the engine. The person I bought it from told me it was a 10-1 engine. I'm just trying to wake it up a little. I believe it is at least 10-1 because of the sound of it. Another friend told me ( he helped with the carb.) that he thought it was higher also. I won't know till I take it apart. I have messed with mopars along time ago (1960's) so I have some basic knowledge. Been away a long time.