Octane

I ran 13.5 to 1 in my 451 a few years ago. I am at 5400 feet so that's like 12.5 at sea level. Started with ported 906 heads at 12 to 1, and it would run mid 13s on the 1/4 mile.Went to ported 915s and headers, with .037 quench. Then it ran 12.40s. So the 1.5 boost in compression and headers with good quench was worth a full second. Ran 20 initial, 38 total on timing. 88 main jets all around in the 850 Holley. It would ping, but if I ran a 50 50 mix of 91 premium with 100 race gas, then it ran fine. The premium up here is only 91 octane. Best running street strip motor I ever had.