Retarded Timing for Low Octane
To provide an inkling of what the effect of retarded ignition timing can be in order to accommodate lower octane gas, I have my numbers.
In the process of setting up my 1691cc Ford Kent Crossflow engine on a dynamometer we first ran it up on 93-octane, unleaded, ethanoled, road gas, with the necessary timing, to 103 ft-lbs of torque at the flywheel. Subsequent runs on 110-octane, full-lead racing gas, at its proper timing, produced 109 ft-lbs of torque at the same RPM. That is a 5.5% increase in engine output.
Note the Crossflow is not fuel injected and ECU controlled; it is fed by two twin-choke Weber side-draft carburetors (40 DCOEs), and in road trim it was originally intended to run on 97 RON leaded. Only the timing by rotation of the distributor was involved, and the jetting stayed the same.