My first suggestion is you shouldn’t need race fuel at that compression ratio. I know it sounds cool, but it isn’t needed. Did you measure the compression ratio or did you use the numbers provided on the piston box? Did you actually measure the chambers? If not, your compression ratio may not be what you think it is. I’m not saying this is your issue but it jumped out at me. As for plug heat range that 12 may be hot. You can try a 10 or even a 9 heat range and see what it looks like.