I run 10.6:1 compression in my 383 and have no problems if I run 91/92 octane. In fact, I had to fill it with 89 octane in a pinch two weeks ago, and still no pinging. My DCR is 8.46:1 which is getting close to the 8.5 edge. But with AFR heads, less timing is more, and 32 degrees total made the most hp and torque. I originally wanted to run a CC XE-274 cam but it put the DCR at 8.67. But the Magnum 280 cam put me under 8.5. I am very happy with my engine combination.