I'm only taking the guys word for it that I bought the motor from. Super avid mopar guy and he said he last checked it at 10.5. But then again, that was back in the 80s the last time he was running it. The motor is still unmolested since he last tinkered with it and all I did was try cleaning the carb to make it fire, which it did. Either way, I still have the ability to make it a higher CR before I decide it's ready to go. Regardless though, I really appreciate the info!