If you live considerably above sea level, another thing to consider is
altitude. Keep in mind that octane serves essentially to reduce the chance
of detonation. Generally speaking, reduced air density provides lower
combustion temperature and pressure, so that higher altitudes require less
If you live in Denver, for example, I've no doubt that you could run 87
octane and your Charger's PCM would never retard the timing at all. But I
don't know where you cross the magic altitude line, though, that allows you
to run 87 octane with zero detrimental effect. 1500 feet? 3000 feet?
With older engines, as air density decreases, the stoichiometry tends to
move to rich, with a lower octane number requirement. This may not be
applicable today, with carefully monitored air-fuel ratios.
Also with older engines, manifold vacuum controlled spark advance, and
reduced manifold vacuum results in less spark advance, though I don't know
if this would have any parallel effect on modern engines.
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