Has anybody done any analysis of knock and timing on low-octane fuels?
I'm thinking in particular about the low-load region that characterizes the way my parents drive: Throttle never exceeds 50%, and engine speed never exceeds 60% of redline. So they have a factory engine that specifies "premium" fuel. But I'm suspecting that with loads like that they will never see a condition where the cylinders get hot enough to knock even on "regular" gasoline. (In which case, I should tell them to save their money and only buy regular gas.) Is there any evidence to support or refute my suspicion?