Dave:
David Geesaman wrote:
[..]
> Well if it weren't for highway on-ramps I could probably do that.
>
> With 89 I still get in it 100% at times and it's never pinged. I could
> try that with 87 but somehow I think that won't work.
.. . . . . . . . . . . .
You can't hear most of the knocking sounds. That pinging is most audible
when you drive uphill or get on the accelerator. Knocking or pinging is
nonetheless harmful to the engine.
The knock sensor retards the timing of the ignition spark. If you used
the pure 80 Octane regular unleaded gas that was common during the 1950s
you would find that your ignition timing would be retarded to 15 to 30
degrees after dead center. With my old Ford with 9:1 Isky heads that gas
would knock nearly all the time. That's bad for aluminum. A MAX has high
compression, aluminum heads and aluminum pistons.
That degree of retardation means that the fuel doesn't have time to burn
completely, and the losses are in torque, low RPM max, and fuel economy.
If pre-ignition, that is, instantaneous burning, occurs, the fuel is
burned inefficiently. The computerized knock sensor ignition and fuel
injector controls make it possible to drive using low octane gas
including 89 octane-rated, and possibly some as low as 80 octane-rated,
however, lower means a risk to the machinery, especially if you drive
with more than just a little throttle opening.
During the 1950s you could even find 60 octane-rated gas. That was
impossible to use due to the pinging. That was probable hexane, pentane,
or with paraffins and who knows what else.
Why not 180 degrees BDC retardation? The engine equipment can't retard
that much due to mechanical limitations.
Read the technical literature. There probably have been more studies
done on auto engine fuels than on any other topic, I would guess. There
are scads of data and re****ts available.
Today, it is the best policy to take advantage of the higher compression
ratio of the engine and higher possible cylinder pressures using the
higher-rated octane gas stated in the car manual. With the proper
ignition advance before TDC, and the proper rated slower burning fuel,
the fuel will be burned slowly and evenly instead of instantly and
explosively. With the recommended fuel rating you will have the best
possible fuel economy, torque and durability.
Ralph Hertle
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