Snatched off another list. >>

Here's an article from Popular Hot Rodding magazine, January 1998. The
article is titled "Petroleum Proof, High-Performance Gasolines" by Scott
Parkhurst.  There also was a small chart in the aricle that showed
effectiveness of octane boosters.

 Octane is a measurement of a fuel's resistance to ignition.
Ideally, the air/fuel mixture will ignite at the proper time and burn
smoothly through the power stroke.  The idea is that one powerful
combustion of the air/fuel mixture is better than several
randomly-ignited small flame fronts.  When you can precisely control the
point at which the fuel will ignite, maximum performance of the engine
can be achieved, and power-robbing knock and ping will be eliminated.
Knock and ping are a result of abnormal ignition, or multiple flame
fronts colliding within the combustion chamber during the compression
stroke.

 All reputable fuel manufacturers determine the octane rating of
their gasoline in the research lab using a special, dedicated single
cylinder engine.  Comparing the gasoline to a series of standard
reference fuels in the test engine results in either a research octane
number (RON) or a motor octane number (MON) depending on a set of
operating conditions.  The RON is determined with the test engine
operating at 600 rpm, at standard barometric pressure, and the intake
air temperature set at 125 degrees Fahrenheit.  RON is primarily used to
address part-throttle knock and ping problems.  The MON addresses wide
open throttle operation and is determined with the test engine spinning
at 900 rpm, also at standard barometric pressure, and the intake air
temperature pumped up to 300 degrees.

 The best predictor of a fuel's performance in a street/strip
machine is the Anti-Knock index (AKI).  This is simply the average of
the RON and MON numbers, or (RON + MON) / 2.  Most all octane ratings
posted at the pumps are determined by this AKI formula, and are the
minimum values you could expect to see.  The minimum octane requirement
of your engine is determined by several variables besides the
compression ratio.  The engine and cylinder head configuration, air/fuel
mixture, timing, coolant temperature, atmospheric pressure, relative
humidity, and ambient air temperature will also affect the octane
required to make your mill produce maximum power.

 The burn rate of a fuel is a measurement of the time required
for complete combustion of the air/fuel mixture.  The notion that octane
ratings affect the burn rate of fuel is about 180-degrees from reality;
bum rate is a function of several variables, and the two are completely
independent, although there is generally a correlation between octane
ratings and bum rates.

 To give you a good example of this, we contacted Jim Wurth from
Sunoco Race Fuels.  He explains, "A perfect example is Sunoco Maximal,
which is our fastest burning fuel, and coincidentally one of Sunoco's
highest octane fuels at 116 (R+M) / 2.  A lot of Pro Stock teams rely on
Maximal for those sub-seven second runs.  When they are turning 9,000
rpm or more, the fuel has to burn pretty quickly to achieve complete
combustion."

 Octane boosters offer little help in the quest for higher
octane.  Most popular street-legal octane boosters claim increases in
octane ratings up to five points, and those boosters intended for
off-road use only claim up to seven points.  That's a lot of octane to
hope for simply by pouring an additive in a tank.  Sunoco told us that
before they launched their GT-100 Unleaded retail pilot program, they
wanted to be sure that a 100 (R+M) / 2 octane street legal fuel would be
of value, and that enthusiasts would not be able to get the same (or
better) results using an octane booster.  Nine of the most popular
retail octane boosters were put through a series of tests to determine
where the consumer could get the most bang for the buck.  The test
results were verified by an independent testing facility, using several
brands of regular unleaded and premium gasolines, just to make sure
everything was legit.

 According to Mark Borosky, Vehicle Test Engineer for Sunoco, "Of
the nine octane boosters tested, none showed a significant increase, and
one actually lowered the octane number of the test gasolines."  Testing
repeatedly showed a maximum increase in octane of 3.5 points by only two
of the six street legal octane boosters when the recommended treatment
rate was blended with lower base 87 octane gasoline.  The best the
remaining four products could muster was less than a one point increase.
"While clearly no one would actually use an octane booster in a low base
octane fuel, we wanted to give the manufacturers the benefit of the
doubt relative to their claims of five-to-seven point increases,"
explained Borosky.

 When tests were performed using 93 and 94 octane fuel, even the
two best products from the previous tests produced a disappointing 1.5
to 2 point maximum increase.  The remaining four street-legal octane
boosters showed less than a .5 point increase.  Those products
designated for offroad use only didn't fare any better than the
street-legal products.  Subsequent tests where the dosage of octane
booster was doubled, tripled, and even quadrupled produced only minimal
improvements in octane, regardless of the base octane number of the test
gas.  In fact, quadrupling the treatment rate of the most powerful
additive produced only a 3.5 point increase in octane when added to 93
premium, resulting in a cost of $3.25 a gallon.

 An alternative path to octane euphoria is to blend gasolines of
different octane levels yourself.  It's easier than you may think, safe,
and the results are predictable.  The formula for mixing gasolines of
the same type is pretty straightforward.  When you mix a 50/50 blend of
two unleaded fuels, simply average the two octane ratings to determine
what's in the tank If you mix 94 and 100, you get 97.  The same
generally holds true for leaded gasolines, assuming the lead content is
nearly equal.

 Blending a leaded fuel with unleaded, however, pushes the octane
up a bit more than the math would suggest, due to the effect of the
lead.  Just a gram or two of lead blended into the unleaded fuel will
raise the octane number significantly.  Commercial leaded racing fuels
contain anywhere from a trace to six grams of lead per gallon.  If you
were to mix 50 percent 110 octane leaded fuel with 100 octane unleaded,
you would actually end up with an octane number around 106 to 107.  Keep
in mind that even the smallest amount of lead or leaded gas line with
unleaded, could spell the end of your catalytic converter or oxygen
sensor.  The same holds true for using octane boosters intended for
off-road use only.  A word to the wise, check for any lead content in
all the additives you might mix with your unleaded gasoline.  And check
with your state emissions regulations for street use.

 We asked Sunoco's Wurth about using aviation fuel in an
automobile engine.  He was emphatic when he said, "Don't do it.  Even
though Sunoco is a major producer of aviation fuel, this fuel is
specifically blended for aircraft engines.  Aircraft operate under very
different conditions than automobiles, and the fuel requirements are
quite different as well.  Aircraft engines generally use very small
pistons and run with in a very narrow rpm range.  There's no need for
transient throttle response in an airplane because after the pilot does
the initial engine run-up, the throttle is set in one position and the
rpm doesn't normally change until landing.  Also, airplanes fly where
the air is cold and thin, and the atmospheric pressure is low.  These
are not even close to the conditions your street machine will see on the
ground.  Also, since most piston-driven aircraft cruise at 3,000 rpm or
so, the burn rate of aviation gas is much too slow for any high
performance automotive applications."

 What is it that makes race gas so different?  What's it made of?
Sunoco tells us their GT PLUS 104 octane unleaded race gas is only 15-20
percent traditional gasoline, and about 85 percent additives!  Actually
there are about 120 different chemicals in GT PLUS.  One reason it isn't
street legal is the high oxygen content.  The EPA requires that the
oxygen content of a street legal fuel cannot exceed 2.9 percent.  GT
PLUS is about 3.5 percent oxygen.  This fuel is light in weight at only
6.14 lbs-per-gallon.  The high oxygen content improves the octane, and
when the induction system is properly calibrated, this fuel will help
make additional horsepower.  The high oxygen content has a supercharging
effect, since 3.5 percent oxygen is the equivalent to about 17 percent
more air.  Different fuels can actually alter horsepower 5-to-10 percent
or more.

 We wanted to to know more about the different types of race gas
Sunoco had, and didn't realize there were five different types of racing
fuel alone.

 GT-100 Unleaded, is a clear fuel with a pump octane of 100, and
will handle compression ratios of up to 12:1, and is street legal in all
50 states.

 GT PLUS, is also unleaded, and is rated at 104 octane.  It is
suitable for compression ratios up to 14:1 and is colored light blue.
It will not harm oxygen sensors or knock sensors in computer controlled
engines.  It is not street legal.

 STANDARD, is a leaded fuel rated at 110 octane, is colored
purple, and is intended for drag racing, road racing, and race boats.

 SUPREME, is also a leaded fuel and is dark blue.  It was
developed to help resist vapor lock and meet the demands of sportsman,
modifieds, offshore powerboats, and endurance racing  where engines
regularly run in excess of 7000 rpm.

 MAXIMAL, we mentioned earlier, is colored red, has 116 octane,
and is leaded.  It is intended for exceptionally high performance
applications like Pro Stock where extremely high cylinder pressures are
common.  Its extremely fast burn rate is satisfactory where rpm exceeds
10,000.

  Now that you're an expert on gasolines, you probably would like
to know where to buy and store the stuff.  If you are fortunate enough
to live in the mid-Atlantic states, you can take advantage of Sunoco's
GT-100 Unleaded retail pilot program and get 100 octane race fuel at
pumps located at select Sunoco stations.  The rest of us have to
purchase from local speed shops, at race tracks, or directly from Sunoco
distributors.

 When you plan on buying fuel in quantity, say a 55-gallon drum,
you'll be happy to know that racing fuel has a shelf life of about a
year, if you store it properly.  The container must conform to all
safety standards, and should be made from metal or polymer.  Make sure
the container is opaque and solid in color.  The white plastic jugs we
see at the track should be used for short-term storage only.  They let
in sunlight, which will affect the fuel.  The lead in leaded fuel and
other chemicals in unleaded fuel are photosensitive, and will dissipate
if they am exposed to the sun.  Keep any container tightly sealed to
prevent evaporation.