I have always thought that manufacturers ran lower than necessary compression ratios because they have to make the car be able to run safely on cheap low octane fuel. Or because the ecu doesn't have a knock sensor.

Is there still gains to be had from lowering the compression ratio on modern engines (evo, skyline ECT ) I would have thought that combustion chamber and cylinder head design advancements (I assume there has been advancements since the 80s ) would have mean that a higher Cr could be used safely?

Please correct me if im wrong as these are just my thoughts on the subject.