All of our Exxon/Shell/Chevron stations sell 93 E10. We also have a Red Dot that sells Ethenol free premium but is 91 octane. I'm currenty set at 18 PSI with the Alky off but occasionally run 23 PSI on Alky. Not fan of the E10 and would like to start using the Eth free. What boost will the 91 support safely.