The two octanes you refer to are research octane and motor octane, not
manufacturers. The motor octane method requires comparing the test fuel
in a very specific motor design against a gas standard such as n-normal
heptane and 100 octane standards. You calibrate with the standards, and
find out where the test motor knocks compared to the calibration. I
believe that any "motor" number above 100 is an extrapolation beyond the
actual data. In any event, the number you see at a California gas
station is required to be the average of the two test method results.
Any motor only need as much octane as it takes not to pre-ignite, or
"ping". Of course, a fine detector is needed to find that exact point
with all the other engine noises in a real car vs a test motor in a
lab. These dtectors are made, and some cars use them to adjust the
timing to max advance without detecting "ping". Any higher octane is
just wasted money, but the gasoline companies really don't want you to
know this. The mid grade gas, unless diluted with alcohol, should
perform well with compression ratios up to 9:1. The Higher 92 grade
should be O.K. to 10, maybe 10.5, but may require some retardation below
optimal. Any C/R above that, and lots of luck. Alcohol will cool the
flame temperatures down, diminishing pinging, but at the cost of power.
Alcohol has only half the available energy in burning than the gasoline
your replacing, but it does run cooler. Refer to any textbook at your
local library, and forget the mythology the gas companies would like you
to believe.
Steve
BTDT
--
Steve Laifman < Find out what is most >
B9472289 < important in your life >
< and don't let it get away!>
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