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How ’bout
AvGas?
The only
aviation gasoline of interest to Corvette enthusiasts is “low-lead 100”
(AvGas LL100). Because of its antiknock rating and low price compared to
leaded racing gasolines, AvGas might seem a good choice for a moderate
octane boost, but closer study raises some doubt.
Because of
its lead content, AvGas must not be used by engines fitted with
modern emissions controls. It renders catalysts useless in short order
and will eventually plug them. AvGas quickly damages most oxygen
sensors, too.
The sale
and use of aviation gasoline is heavily-regulated. Most aircraft fuel
dealers refuse to put AvGas into anything other than an aircraft fuel
tank. There is a legal gray area that has some vendors willing to
dispense AvGas into approved containers if they believe the end use of
that AvGas is fueling an aircraft engine. This loop-hole is how some
people obtain AvGas for automotive use.
Aviation
gas is formulated for large-bore, long-stroke, low rpm engines which run
at high altitude. While AvGas’ higher octane is useful, smaller-bore,
shorter-stroke, high-rpm, non-cat, Corvette engines requiring 92-98-oct.
will perform better on racing gasoline. AvGas has lower volatility so,
used in proportions higher than about 40%, part-throttle drivability and
cold starts may be compromised. AvGas has a lower specific gravity so it
will require a change in air-fuel ratio calibration for the engine to
perform at its best. LL100 is blended with a high percentage of
aromatics. That reduces throttle response–not really an issue with an
aircraft engine but certainly an issue in a high-performance automotive
engine.
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Most small airports that cater to general aviation will
sell AvGas through fueling facilities such as this. If
you decide to accept the compromises of aviation
gasoline, make sure what you buy is “100” or “100LL”. Do
not use “Jet A”. That’s jet fuel, a form of kerosene,
and burning it in an automotive engine will cause
serious damage. Image: author. |
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The “Aviation”
antiknock rating system is different than the MON rating. 100-oct. on the
aviation scale, equals 98.8 MON. The biggest limitation of LL100, when used in
very high-compression or high-boost, race track applications requiring leaded
gas is octane. “For those applications, AvGas,” Tim Wusz told us, “is
short on octane compared to most (leaded) racing gasolines. Many racing
engines have more spark advance at low rpm and/or during lean, part-throttle
operation than AvGas and even some (unleaded) racing gasolines can
handle. The result is detonation.”
Bottom line: AvGas
is ok in off-road situations were a leaded fuel of no more than 98 octane
required, ultimate performance is not important and you can accept possible
drivability quirks. |
Blend Your
Own Race Gas? Not.
If you’re a
regular reader of the VetteNet mail list or visitor to the techie boards
on the Corvette Action Center, you’ve heard of other do-it-yourself
additives said to improve gasoline. Unfortunately, a lot of that is
urban legend. The executive summary of “DIY race gas” is: mixing it can
be dangerous. You sometimes loose performance. You don’t save money.
Some of
these DIY additives are: aniline, benzene, toluene, xylene and propylene
oxide. Forget the first two. Both are highly toxic. Aniline is absorbed
through the skin and impairs your blood’s ability to carry oxygen.
Handle aniline improperly and you die. Benzene is a carcinogen, so
you’ll die after improperly handling it, too–it’ll just take longer.
Their toxicity and that they are used in making drugs has aniline and
benzene Federally-regulated and not available to the public.
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The aromatic hydrocarbons (“aromatics”), toluene and xylene are octane
improvers. Significant amounts of toluene and lesser amounts of xylene are
already in pump and racing gasolines. Both are available from automotive paint
suppliers. Both are mildly toxic. Work with them wearing chemical-resistant
gloves and in a ventilated area. If there’s any question about ventilation, wear
a respirator.
In
California, law restricts aromatics to 35% of a gasoline blend.
Elsewhere it may be as much as 40%. The effect additional
toluene or xylene has on pump gas is unpredictable for two
reasons: 1) the octane boosting ability of both is less
effective on premium pump gases than on regular grade gas
because of the aromatics premium gases already contain, 2)
toluene and xylene have high octane ratings alone but may have
lower octane when blended with other gasoline components and
must be carefully tested when mixed with other gasoline
components.
Toluene and xylene have specific gravities higher than pump gas
so the more of them you add, the leaner you need to calibrate
the engine’s air/fuel ratio. Once you calibrate for toluene- or
xylene-spiked, DIY racing gas; don’t go back to running
conventional gasoline until you recalibrate to a richer mixture
or you’ll be burning pistons.
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“Adding more toluene,” Tim Wusz told us, “will increase
the octane numbers of the gasoline, but when you get
above 45 or 50%, throttle response is poor and the flame
speed is reduced to where increasing amounts of fuel are
still burning as combustion gases are forced out the
exhaust valve. Once that happens, power is lost, not
gained.” Image: author. |
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Both
have less volatility, so engines burning gasolines laced with high
concentrations of them can be more difficult to start when cold.
In addition
to handling, mixing, calibration, drivability and performance problems
associated with DIY race gas, it has a lousy business model, too. A
late-model Corvette with a medium-boost, aftermarket supercharger kit at
the drag races on a warm day might need 97.2-oct. to keep the engine out
of detonation. Toluene, used as a blending component, is 103.5-oct. To
make 10-gal. of 97.2-oct., DIY race gas (1:1, 91-oct. unleaded and
toluene) costs $42.80. Do it with 91 and 100 unleaded gasolines, you mix
3:7 for $32.05. Because a 1:1 mix of toluene and pump gas costs you
performance and throttle response due to slow burn speed; not only is
DIY race gas a lot more expensive, but it won’t perform as well, either.
The
economics of xylene are worse than toluene. Xylene from industrial
sources is “mixed-isomer” and has less octane boosting ability than
toluene and a higher unit cost. The higher octane, single isomer
varieties of xylene, typically obtained through science and laboratory
supply businesses, are obscenely expensive, upwards of $100 per gallon.
Misunderstanding surrounds propylene oxide. Common uses for it are
pesticide and fumigant. While the EPA lists it only as a “probable
carcinogen,” ingesting propylene oxide will at least make you sick and
can cause coma or death. Use care when handling it. Some racers are
under the impression “P.O.” is an octane booster, but it is not. It is
an oxygenate that works like nitrous oxide but not as well. “It will
improve performance,” Wusz stated, “but the mixture must be
richer to take advantage of that. PO is more effective than MTBE but
less effective than nitrous. The downsides of PO are: 1) it attacks
plastic and rubber parts in fuel systems and 2) its low, 95 deg. F
boiling point gives it a tendency to easily escape from a blend leaving
the DIY race gas blender with a gasoline which he thought contained a
certain amount of PO, but in reality, may have retained far less of it.
This makes tuning exceedingly difficult.”
Bottom
line:
brewing your
own race gas a foolish move for a lot of reasons. You’re better off
buying it ready-made.
Racing Gas
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Our dyno test showed the best gasoline choice for a
computer-controlled car that sees a little detonation on
hot days is a mix of racing gasoline and pump gasoline.
Image: author. |
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Many think racing gasoline is just for racing but, in recent
years, the term has also come to mean high-octane, unleaded used by
street cars. The obvious reason to use race gas is higher antiknock
rating, but just as important is: it’s an optimum, balanced blend of
hydrocarbons and additives intended to produce the highest possible
performance from a high rpm, automotive engine. It’s better than pump
gases fortified with octane boosters, better than AvGas, better than
pump gases spiked with store-bought aromatics and the only alternative
if you want your engine to perform best. There are 10 vendors of racing
gas in the United States. Most sell through distributors, however, in a
few urban areas, some refiners sell racing unleaded at retail service
stations.
“Entry-level” racing gasolines are usually unleadeds of about 100-oct.,
R+M/2. Eight of the 10 companies sell it. Octane ratings vary from 93 to
99 MON, a significant gain over the approximately 88 MON of the best
pump gas. Racing unleaded is the perfect choice if the engine in your
Corvette needs a moderate octane boost. It is good for engines with
superchargers of moderate boost, modest nitrous oxide injection systems
or any modifications that increase cylinder pressure somewhat over stock
levels.
We asked
Tim Wusz about Rockett Brand 100 and he said, “This product has been
used in endurance (sports car) racing in four-inch bore engines
with 14:1 compression ratios and aluminum heads. With cast iron heads,
compression ratio should be limited to 12:1. It can be used in current
performance street cars. Historic muscle cars can also benefit from this
product which easily services the 11:1 compression ratios of many
engines from that era.” |
When
late-model Corvette is run hard on hot days, as shown in our tests on
the SuperFlow Auto-Dyn with the ZR-1 and later with a Z06, engine
computers will often enable spark retard. This is because the car’s
engine controls are calibrated for aggressive spark advance to get best
performance in cool weather, then “save” the engine with spark retard
when mild detonation is sensed during high-load/hot-weather operation.
Because of the retard, their performance is reduced slightly and coolant
temperature is slightly higher.
On cool
days there’s no problem, but in warm weather, the engine will get a
little detonation, the knock sensing will retard spark and performance
will drop slightly. A small amount of unleaded race gas mixed with
premium pump gas (start at 1:5, then work up) is the best way to
eliminate this problem, short of engine modifications, changes in
calibration or moving to a cooler area.
Does this
work in practice? At our shop, we drained our test Z06’s fuel tanks,
added 10 gallons of Rockett Brand 100 then drove 50 miles to a session
on the Auto-Dyn at Westech. The IAT was 106°F and the dyno read 9.5hp
more than the first test on straight unleaded premium. After lunch, we
“thinned” the remaining Rockett 100 down to 94.6-oct. by mixing it 2:3
with Chevron 91-oct. unleaded and ran again. The IAT was now 109 and the
power was up 7.5hp over straight pump gas. In all runs of this second
round of tests, our Vetronix Mastertech showed no detonation. Clearly,
in hot weather, unleaded racing gas works well as a detonation fighter.
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Some think unleaded race gas is prohibitively expensive but, for
a given octane, compared to pump gas spiked with pour-in
additives; its economics are usually more favorable. Don’t think
you have to use racing unleaded at full strength, either. If
your engine only needs 94.0 octane, mix it 1:2 with 91-oct. pump
gas. It’s relatively easy to “math out” the proportions of the
mix you want and some race gasoline suppliers have mixing
charts, such as the ones from Rockett Brand Racing Fuel
reproduced here, to make the process easier.
While it is true that your engine only needs as much octane as
is necessary to keep it out of detonation, there are cases were
a particular engine will run better on a high-percentage mix or
straight 100 unleaded in spite of not needing additional octane.
There’s no set rule on this and we suggest, once you’ve
determined the ideal mix of pump gas and 100 unleaded to keep
you out of detonation that you, also, run a test of straight 100
unleaded. In some cases the different components in the 100
unleaded and its slightly faster burn speed will improve
performance even more.
A
few of these unleadeds–Rockett Brand 100, for example–are
street-legal in all 50 states. Another attractive feature of
some, like the Rockett Brand 100 sold at Rebel stations in
southern Nevada and at Gas City stations in the Chicago area, is
the convenience of buying high-octane, street-legal gas at a
service station–no searching for distributors, no hauling cans
around and no storing gas in your garage. Just drive up to to
the island, stick the nozzle in the tank and pump your Corvette
full of 100-oct. unleaded race gas.
The
bread-and-butter of the racing gasoline business is leaded fuel.
It is the best choice for racing engines requiring more than 100
octane. All vendors marketing leaded race gas have several
grades available. |
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Click Chart for Larger Image
or
Download Acrobat |
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Some
racing gasoline vendors make available charts like this
to assist users in mixing unleaded racing gas with
premium unleaded pump gas. Rockett Brand Racing Fuel has
charts for 91-, 92- and 93-oct., too. Graphic: Rockett
Brand Racing Fuel.
DOWNLOAD CHARTS - PDF
Format
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“We have
four leaded race fuels:” Tim Wusz continued, “The first three are Rockett Brand 111, 114
and 118.
“111 is our
highest volume racing gas. For 53-years, it was the official gasoline
for NEXTEL Cup Racing and all other NASCAR series. It’s used by lots of
‘Saturday night’ racers in all types of competition using all varieties
of engines.
“114 is
more for bigger engines. Drag racers with big motors in SuperComp and
SuperGas like it. It’s good because large engines often need more
octane. It’s for medium supercharged applications, too.
“118 was
originally developed for ProStock and worked well until so-called
‘fast-burn’ gasolines came along. The 118 is ideal for high-boost,
supercharged applications. It’s also good in engines running a lot of
nitrous oxide. The 118 has a little faster burn characteristic than the
114, but not as fast as our fast-burn gas.
“We have
another fuel, ProStock+, that’s really better than the 118 for
performance in certain applications but, because of different burn
characteristics, it’s around 114 octane. It’s a very fast-burning gas
for use in very high-rpm, normally-aspirated engines. It was developed
for NHRA ProStock. Because of their high rpms, they need the faster burn
speed, otherwise you open the exhaust valve and loose a lot of unburned
hydrocarbons. If you increase the gasoline’s burn speed, you use that
stuff, rather than flushing it out the exhaust, and the engine makes
more power.”
Most of the
other vendors have between 3 and 5 grades of leaded race gas and one
company, VP Racing Fuels, has a mind-boggling, 14 different grades. If
you are having difficulty making a decision about racing gasoline,
contact the suppliers of these products for detailed information and
recommendations.
The Future
The United
States EPA announced in late 2000 it intends to discourage off-highway
use of leaded gas. EPA is putting pressure on the general aviation
community to accept unleaded AvGas and it also wants motorsports
sanctioning bodies, particularly NASCAR, to adopt unleaded gasoline. You
can bet, if NASCAR goes unleaded, other sanctioning organizations will
follow. We asked Tim Wusz what plans racing gasoline vendors have if
NASCAR goes to unleaded fuel.
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“We
did test work over five years ago with unleaded gasoline in
Busch Grand National cars without any significant adverse
effects. For current, 12:1 compression ratio engines required in
NASCAR NEXTEL Cup, Busch and Truck Series, our hundred octane
unleaded is adequate, but we have to convince the racers and, to
do that, we need the support of the sanctioning bodies. A few
years ago when compression ratios were 14:1, we tested unleaded
in a Winston Cup engine that had pressure transducers in all
eight cylinders. We found the 100-oct. unleaded ran with no
detonation.
(Ed note: this test was under wide-open throttle conditions and
included no part-throttle, lean mixture operation typical of
running in caution periods or of engines not calibrated properly
for part-throttle operation) This engine was optimized with
34-degrees spark advance. Then, we started bumping the timing
up. We got up to 42-degrees before there was any indication of
detonation. Normally, two degrees is an octane number so we had
a cushion of about four octane numbers.” |
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“At Rockett, we have the technology to make a
105-octane unleaded but right now, the demand for it
just isn’t there.” Tim Wusz commented. Image: author |
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If
there is a conversion of motorsports to unleaded
gas, perhaps the first place we’ll see it is in
NASCAR Winston Cup racing. The huge appeal of NASCAR
would be a major factor in marketing the switch to
unleaded gasolines to motorsports, however, at this
point in time (late-2004) it doesn’t look like a
switch will happen anytime soon. Image: author |
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In NASCAR
and other forms of racing that put similar demands on gasolines, the
change to unleaded may be more of a cultural challenge, however,
unleaded gas might be a significant technical problem in other parts of
the sport. It would be a tough sell in some categories of drag racing,
as well as a few other motorsports that use gasoline engines with very
high compression ratios, high levels of supercharger boost, big shots of
nitrous, large combustion chambers or any combination of these.
“The Clean
Air Act has always exempted motorsports from a mandated conversion to
unleaded,”
Wusz continued, “so all the EPA and other governmental entities can
do is discourage the use of leaded gasolines and request a change to
unleaded.” He went on to say that the November 1999 election of
President George W. Bush changed the landscape as far as the EPA’s
interest in seeing a conversion to unleaded racing gasolines was
concerned with the threat being greatly reduced.
At this
writing (early December, 2004), with Bush going back to the White House
for another four years, motorsports seems pretty safe from new pressure
to go unleaded, however, if in '09, after the next presidential
election, the winds of change start blowing again; Rockett Brand Racing
Fuel and other providers of racing gasolines will be ready with an
unleaded products suitable for NASCAR and many other types of
competition.
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Sources:
Sources:
Rockett Brand Racing Fuels
22349 La Palma Av.
#104
Yorba Linda CA 92887
800-345-0076
info@rockettbrand.com
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Red
Line Synthetic Oil Corporation
6100 Egret Court
Benicia CA 94510
800 624 7958
www.redlineoil.com |
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Vetronix Corporation
2030 Alameda Padre Serra
Santa Barbara, California 93103-1716
www.vetronix.com
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Westech Performance Group
Unit C,
11098 Venture Av.
Mira Loma CA 91752
909-685-4767
www.westechperformance.com |
VP
Racing Fuels, Inc.
Box 47878
San Antonio TX 78265
210 635 7744
www.vpracingfuels.com |
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