compression ratio doesn't mean much anymore, you have to look at the camshaft profile and valve timing.
how long the intake valve stays open as the piston comes upward on the compression stroke will have the most affect on cylinder pressure, and cylinder pressure is what determines octane requirement. You also have to factor in volumetric efficiency (valve overlap) which changes with rpm. Ignition timing gets misunderstood when talking about octane requirements. It's just a method of controlling detonation under certain operating conditions- by retarding ignition timing you lessen cylinder pressure. You want the maximum advance in timing in order to build the greatest cylinder pressure which then yields power and combustion efficiency. Whether the engine maker designs their ignition system based on 87 or 93 octane is
But i'm sure all ignition systems today have knock retard built in so if you have lower octane gasoline that would cause pinging under maximum ignition timing, the computer would sense it, back off timing, and the engine runs fine without pinging. The way to know is get a laptop or handheld scanner capable of pulling KR numbers from the computer. I'd bet everyone here running 87 octane probably has a few degrees of KR. The norm for the LS1 drivers who run 91/93 octane is a couple degrees KR. It also largely depends on outside air temps and engine temps too.
how long the intake valve stays open as the piston comes upward on the compression stroke will have the most affect on cylinder pressure, and cylinder pressure is what determines octane requirement. You also have to factor in volumetric efficiency (valve overlap) which changes with rpm. Ignition timing gets misunderstood when talking about octane requirements. It's just a method of controlling detonation under certain operating conditions- by retarding ignition timing you lessen cylinder pressure. You want the maximum advance in timing in order to build the greatest cylinder pressure which then yields power and combustion efficiency. Whether the engine maker designs their ignition system based on 87 or 93 octane is