I had a conversation today with a member of the Early Mustang Club here in Colorado. He said that he's running 10.5:1 compression and is running 85 octane without a whimper from the motor. He said it was due to the altitude. Basically saying that, yes, the motor may be 10.5:1 @ sea level, but... take it up a mile high dropping the air pressure, and having less O2 in the air also, drops the equivalent compression to 9.5:1. Thus the ability to use regular pump gas. Truth or BS? Judges??
Scott Williams '66 High Country Special