Whats the highest compression I can go without having issues on 91 octane? Also keep in mind that its gets pretty damn hot here during the summer.

If you're wondering, Cali = Liberal = 91 highest available grade

 

I can't really answer your question, but here's a thread I ran across while doing a search of my own.

https://ls1tech.com/threads/showflat...;Number=419628

 

You can get away with 11-1 up in sac town. Those 100 degree summers realy suck. I used to have 11.8-1 and it pinged like a popcorn machine. 11.25-1 I would say is max for 91 octane, but it depends on how much timing you are running.