You may see some power loss due to the timing being retarded if the engine
controller detects pinging.

Glenn Beasley
Chrysler Tech

If it's the same engine they put in the 300M's, then my 2000 300M does
just fine on 87 octane.  That's all I ever use.

The horsepower, torque, 1/4 mile times they publish are probably using
89 or 91 octane.  That's why they say the recommended octane is 89 -
so that you don't complain to them when you don't get the 1/4 mile
time that Road and Track says they got.

Recommended is basically bullshit.  It's when they say "required" that
you have to sit up and take notice.

With electronic timing and ping sensors, and the fact that the lowest
grade of gas you can find is basically 87, even engines designed to
use 89 (which I'm sure the 3.5l isin't) can get by with 87.

You're gonna spend over 20K for your new Charger.  The added expense of
10 cents or so a gallon isn't going to be much compared to the cost of
the car itself.  I have a 2004 Hemi Durango that also requires 89.  Just
not enough to worry about compared to how much the Durango cost me.
Total cost of ownership is what matters to me.

However, it does run fine on 87 unless I'm towing or traveling in steep
terrain in hot weather.

If the ignition retards enough, your mileage will go down. Depending on
the price of fuel, the decrease in mileage may equal or surpass the fuel
cost of the higher octane.

They don't recommend it for fun; after all, the recommendation hurts sales.
Don't buy a car that you are willing to treat properly.

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
octane.

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.

Marcus