Compression

Rule of thumb I was always told to be able to run 87 octane without pinging was 9.6:1 with Steel Heads and 10.6:1 with aluminum heads. Each setup is different, I know I built a 440 with final about 9.7:1 final CR, and had no pinging on mid-grade. Ran quite well at Mile high (Bandimere) 13.95.