RE: Old new car question,please see what you think
Octane ratings exist purely to describe the anti-knock characteristics of the fuel, or it's tendency to burn in a uniform or controlled manner, and have nothing to due with the energy characteristics of the fuel. The energy value of fuel is a much more complex science. The higher the octane, the lower the energy value. This is further compounded by Ethanol, which adds octane at the expense of energy value. It sounds backwards, but that's how it works.
Most modern vehicles are desingned to run on 87 octane, but factors like driving habits, vehicle condition, weather, etc. can have an effect, so sometimes higher octane is needed to prevent knock. Some performance cars (particularly turbo/supercharged) need higher octane fuel, because the pressures inside the cylinders is higher than that of normal cars. Lower octane fuel can light off when it's not supposed to in these vehicles (detonation), and cause all sorts of chaos.
Many argue that there is no benefit to be had running a higher octane, but there's also a lot of people who say they can feel a difference. My Wrangler pings on 87 octane, and it has since day 1, even though that's what it's designed to run on. So Irun 89 or 93 in it. Jeep sayus the ping is normal and within the realm of acceptable, but Iprefer to not have it ping at all. It costs me maybe $2 extra, Ifeel it's worth it. In my 55 Chevy, Ihave to run 93 octane due to it's higher than normal compression and timing curves.