jeff@qubix.UUCP (Jeff Buchanan) (06/12/84)
I need some information from some of you chemist/petroleum Engineer
types. How does one compare the octane rating of todays gasoline to that of
1973? Around the time that gas started to lose it's octane, (1973-ish)
the rating method was changed. Today the rating you see on the pumps is
Research method + Motor method / 2 = octane number. I remember that the
old rating was either research or motor but I can't remember which. I also
remember the advertised octane then was "100+". That was the higher number
of the two (research and motor). So typical premium gas like Texaco Skychief
and Enco Extra was about 101. Sunoco was about 104, or so they claimed.
If the typical 92 octane gas available today was rated the same as it was
in 1973, (before the change in rating method) what would it's octane number
be? I understand that the way gas is rated (motor or research) hasn't
changed, only the way the final number is determined (above formula).
Everyone knows that gas today has lower octane than it used to, but since
the rating method has also changed, it is hard for me to see HOW MUCH it
has been lowered.
Also, I would like to get some opinions as to the effect on power
output of engines with the low octane (92) gas. Obviously if you have a
high compression engine (10.5-to 1 or higher) you must tune differently
if you switch from high octane to low octane gas. But if you were to take
a typical engine from the late sixties, say a 435 HP 427 Chevy and tune
it for maximun HP on the old high octane gas, then tune it for max power
on todays low octane (92) gas, what if any horsepower difference would
you see on the dyno?
The difference talked about between high and low octane gas is that
high octane burns slower and more evenly. This means you can dial in more
spark advance and a high compression ratio without power robbing knocking
and pinging. I understand this, but that doesn't necessarily tell me that
high octane gas has more potential energy per unit volume than low octane
gas. I have more than academic interest in this issue. I have an L-88
engine in my '66 Vette that pings terribily with 92 octane. In 1973
it didn't, although I changed no components (except for rebuild items
like rings and bearings). This is comparing the now and then engines
immediately after rebuild. Same cam, carb, piston, gasgets, etc. So
the only explanation is gas. Now, I know I can solve the problem of
knock with octane booster, but my main question is will bringing up the
octane rating of today's gas with booster necessarily mean it will have
the power of 1973 !00+ gas?
--
Jeff Buchanan @ QUBIX Graphic Systems, Inc., Saratoga, CA.
...{decvax,ucbvax,ihnp4}!decwrl!
...{ittvax,amd70}!qubix!jeff
decwrl!qubix!jeff@Berkeley.ARPAtoma@tekchips.UUCP (06/15/84)
------------- Subtract 4 from the old Research Method octane numbers to get current values. This means old Premium gas would be about 96 and old Regular would be about 90. Lower octane fuel does have more potential energy per unit volume. I am sure that if it were not for the push to get rid of leaded gas (the cheap way to raise octane) all the cars today would require premium because smaller engines could be used to obtain the same power with less fuel consumption.
joe@zinfandel.UUCP (06/19/84)
#R:qubix:-119300:zinfandel:3200067:000:979 zinfandel!joe Jun 14 08:44:00 1984 Hi. What I know on the subject is that the motor method is the older of the two systems, and is still used. It involves a standard single cylinder engine run just hard enough to make the fuel tested detonate. This level of engine output is compared to the performance of pure octane, a relatively good performer. For exact percentages they find the percentage of octane in a mix of octane and pentane ( a very willing knocker ) that performs as well as the tested fuel. Fuels of other composition can perform better than pure octane so "150% octane" gas is possible. The other method "rational method" is a sophisticated chemically based formula for calculating the knocking potential, again as compared to pure octane. As the variables involved in knocking are many these are both guides but not absolute predictors. In practice they are consistant however, and usually don't vary for the same fuel by more than one or two points. Joe "I HEART MY DOG'S HEAD" Weinstein
wookie@alice.UUCP (06/20/84)
The engine test method used for the octane ratings was in an engine with variable compression ratio. The ratio was increased until detonation began and from that info the octane number was deduced by comparing the fuel under test to pure octane. Keith Bauer White Tiger Racing