Racing Gasoline Verses Aviation Gasoline
written by, and thanks to
Tim Wusz
76 Products Company




I am going to attempt to address the controversy of aviation gasoline verses
racing gasoline for use in race cars. Some racers use aviation gasoline which
is fine for some applications but does have shortcomings. There are several
grades of aviation gasoline (avgas) that we must identify before going any
farther.


1. Avgas 80/87: this product is used in low compression ratio aircraft
engines, contains little or no lead, is red in color, and should not
be used in any automotive engine due to a low motor octane number of about 80.

2. Avgas 100/130: this product that can be used in some automotive engines. It
has both research and motor octane numbers slightly over 100. Avgas 100/130 is
green in color, contains four grams of lead per gallon, and is becoming harder
to find.

3. Avgas 100 LL: the LL stands for "low-lead" which means two grams per
gallon, low compared to the avgas 100/130 that it was designed to replace. It
has research and motor octane numbers very similar to the 100/130 product
previously discussed. The color is blue. This product sometimes has a high
level of aromatics which can contribute to lazy throttle response and
dissatisfaction of the consumer.

4. Avgas 115/145: this product was developed for high performance piston
aircraft engines used in world war II and in the Korean war. It is very hard
to find anymore due to lack of demand although it is of very high octane
quality. The color is purple.

The remainder of this discussion will assume that our basis for comparison
with racing gasoline is avgas 100/130 and/or 100 LL since they are both
available and have acceptable octane quality for limited applications. When
the word "avgas" is used, it will refer to avgas 100/130 or 100 LL.

Avgas is less dense than most racing gasolines. Instead of weighing about 6.1
to 6.3 pounds per gallon like racing gasoline, it weighs 5.8 to 5.9 pounds per
gallon. The racer must compensate for this by changing to richer (larger) jets
in the carburetor when changing from racing gasoline to avgas.

The other major difference is octane quality. Avgas is short on octane
compared to most racing gasolines. Many racing engines with "quick" spark
advance curves or with no centrifugal advance have more spark advance at low
rpm than avgas and some racing gasolines can handle. The result is detonation,
especially during caution periods in circle track racing because all of the
spark advance is "in", rpm is low, and part throttle air fuel ratios are too
lean for the operating conditions. If the driver does not "work" the throttle
back and forth, pistons can be "burned" which melts away part of the aluminum
piston material. Inadequate octane quality is one of the quickest ways to
destroy an engine. Pistons can be severely damaged during one acceleration
where detonation is present and the racer may not know what is happening until
it is too late.

For maximum performance and power from a racing engine, racing gasoline will
normally provide better performance than avgas.Avgas can be a good gasoline
for some applications, but since most racers do not know the octane
requirement of their engines, they would be better off with a "real" racing
gasoline that will give them the overall resistance to detonation that they
need to protect their investment. If someone has spent from $15,000 to $50,000
or more on their racing engine, it is foolish to cut corners on gasoline be
sure you have a gasoline with adequate octane quality.