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Gasoline Digest (Continued)
What you need to know about fuel for Corvettes and other high-performance cars.
by Hib Halverson
©2002 all rights reserved
No use without permission

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.

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.

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 Forum, 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.

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 30% 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 lower octane when blended 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. 

"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.

Both have less volatility, so engines burning gasolines laced with high concentrations 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

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. 

Our dyno test of the 1995 ZR1 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.

It is good for engines with superchargers of modest boost, moderate nitrous oxide injection systems or any modifications that increase cylinder pressure somewhat over stock levels.

We asked Tim Wusz about 76 Competition 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 K&N Dynojet with the ZR-1, its engine computer 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 ZR1’s fuel tank, added 10 gallons of 76 Competition 100 then drove 50 miles to K&N for a second session on its Dynojet. The IAT was 106°F and the Dynojet read 9.5hp more than the first test on straight unleaded premium. After lunch, we "thinned" the remaining Comp 100 down to 94.7-oct. by mixing it 1:2 with 76 92-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 at K&N, our Vetronix Mastertech showed no detonation. Clearly, in hot weather, unleaded racing gas works well as a detonation fighter.

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 more favorable. Don’t think you have to use racing unleaded at full strength, either. If your engine only needs 94.5 octane, mix it 2:4 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 76 Performance Products 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–Competition 100, for example–are street-legal in all 50 states. Another attractive feature of some, like the Competition 100 sold at selected 76 and Circle-K stations in urban areas, 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 yourCorvette full of 100-oct. 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.


Click Chart for Larger Image
 Download Acrobat

 Some racing gasoline vendors make available charts like this one, for  91-oct pump gas and 100-oct unleaded racing gas, to assist users in mixing unleaded racing gas with premium unleaded pump gas. 76 Performance  Products has charts for 92- and 93-oct., too. Graphic: 76 Performance Products.
PDF Format

Here’s another guy who depends on and wins with 76 Competition 110: NASCAR 2002 Rookie of the Year contender, Jimmie Johnson. Throughout his stock car career, he’s run with 76 racing gasoline and it helped him drive to victory at the NAPA 500 at Fontana, California in 2002. It was his first win and came after only 15 Winston Cup starts. Johnson drives the # 48 Lowes Chevrolet Monte Carlo owned jointly by Winston Cup Champion Jeff Gordon and Rick Hendrick. Image: author.

"We have four leaded race fuels:" Tim Wusz continued, "The first three are Competition 110, Super Stock 114 and ProStock 118.

"110 is our highest volume racing gas. It’s the gasoline used in Winston 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 and ProStock Truck. 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 76 Performance Products has if NASCAR goes to unleaded fuel.

"We did test work over two 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–Winston 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."

"At 76, we have the technology to make a 105-octane unleaded but right now, the demand for it just isn’t there." Tim Wusz commented.

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.

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 (mid-2002) it doesn’t look like a switch will happen anytime soon. Image: author.

Most of the research for this article along with the initial interview with 76 Performance Products’ Tim Wusz took place in February of 2001. In April of 2002, during an interview at the NASCAR NAPA 500, we once again talked with Tim Wusz and took up the issue of the conversion of major motorsports to unleaded gasoline.

"The Clean Air Act has always exempted motorsports from a mandated conversion to unleaded," Wusz told us, "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 2001 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.

While in early 2001, it seemed an environmentally activist, Gore administration would come to power and push NASCAR and other sanctioning bodies to unleaded fuels, the more conservative Bush administration is conforming to the intent of the Clean Air Act and seems content let motorsports continue to use leaded racing gasolines. While in early 2001, the switch seemed a probability, in mid-2002, it now seems a distant possibility.

Nevertheless, if the winds of change start blowing again, 76 Performance Products will be ready with an unleaded racing gasoline suitable for NASCAR and many other types of competition.



76 Performance Products
22349 La Palma Av.
Yorba Linda CA 92887

K&N Engineering
PO Box 1329
Riverside, CA 92502
Red Line Synthetic Oil Corporation
6100 Egret Court
Benicia CA 94510
800 624 7958

Vetronix Corporation
2030 Alameda Padre Serra
Santa Barbara, California 93103-1716



VP Racing Fuels, Inc.
Box 47878
San Antonio TX 78265
210 635 7744

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