Napoleon1991

Im looking to try one heat range cooler on my spark plugs due to getting some detonation. I currently run auto lite 85s and i was wonderig what the next cooler plug would be. Ive done some looking online but its not easy to find a chart showing the heat range of the different spark plug part numbers. Btw, i have an olds 403 with about 10:1 compression. I run premium gas and have backed the timing off 5 degrees from the spec (which i was told is 20 degrees) and i still get some pinging on hot days. Thanks