On Thu, 20 Jul 2017 18:49:56 -0400,
wrote:

BTW, most people trust their own intuition more than they trust facts to
the contrary, so you might be surprised when you read the part about what
they found out when they tested cars that SAID to use high octane fuel, but
CR tested them with the low-octane (regular) fuel instead.
http://www.consumerreports.org/cro/c...nomy/index.htm
Under some conditions, ie. high temperature,and heavy load, the 2 cars
referenced will detune due to mild detonation on regular gas. Rhis
WILL cause a (possibly small, but measurable) decrease in power output
and fuel economy. It will not show up much on thir tests, but load the
car to capacity and drive up independence pass, or any other long hard
grade and it WILL be noticeable.

The difference between "premium recommended" and "premium required"
is "premium recomended" can compensate for low octane by detuning and
not cause any damage, while "premium required" cannot compensate
enough. Under "normal" driving you may get away with regular gas on
either car

Just to let you know, my car "requires" premium (91 I believe) and yet, it
works just fine on 87 (yes, it has knock sensors so it retards the timing
"if" it knocks).

The question I've always wondered is how can I ever tell if it *did* have
to retard the timing.

I am told if I had better equipment, I *might* be able to read that out of
the ECU. All I have is OBDII stuff, so, that's beyond my capability.