Is Avgas a cheap alternative to racing fuel?

Why not run avgas in your car? After all, it promises higher octane with no ethanol at a reasonable price, and it’s conveniently as close as your local airport.

“People think they have found a glitch in the system, like it’s a cheap alternative to race fuels,” notes Zachary J. Santner, manager of production engineering and business optimization at Sunoco. But as he notes, there are some factors to consider–and reasons why this fuel might not be best for your car.

Most of the piston-driven airplanes out there operate on what’s called 100LL, a non-ethanol fuel that carries a 100-octane rating. That’s its Motor Octane Number, Santner explains, as its Anti-Knock Index, the number used for fuels intended for automobiles, would be closer to 105. (Santner notes that mixing 110-octane race fuel with a pump fuel–a common recipe–would also yield about 105 octane.)

So, that first concern: lead. Even though 100LL is billed as a low-lead product, it still contains lead, meaning it’s not acceptable for cars running catalytic converters and oxygen sensors.

More concerns: Avgas contains additives–like ones designed to combat static and icing–that your car doesn’t need.

Unlike race fuels, avgas is also designed to operate at lower engine speeds and constant loads. As a result, avgas often contains higher percentages of aromatics, the slower-burning compounds used to raise octane. (Sunoco’s race fuels, by comparison, use high amounts of faster-burning C5-C9 paraffins to keep up with high-rpm race applications.)

Then there are some logistical concerns: Can you roll up with your truck and trailer at the local airport?

Avgas might work fine in your race car, Santner notes, but a race fuel would be a better fit. Plus, running a race fuel would provide the right solution for nearly any engine. “With race fuel, we have 25 different options, whereas 100LL avgas is just one option” he adds.

Comments

APEowner GRM+ Memberand UltraDork
6/5/24 12:47 p.m.

A lot of Formula Ford engines (including mine) are run on 100LL. it's a good fit because they're old pushrod motors with no cats or O2 sensors and, at least at my local airport I can pull the truck and trailer right up to the pumps and fill the cans.

mfennell HalfDork
6/5/24 1:06 p.m.

My friend with 30ish mostly carb'd motorcycles runs them on 100LL because it can sit forever. We have no access to non-ethanol gas beyond buying VP T4 for $120/5 gal pail.

californiamilleghia UberDork
6/5/24 3:32 p.m.

is AV gas color tinted like "farm" diesel is tinted red ?

wearymicrobe PowerDork
6/5/24 3:48 p.m.

mfennell said:
My friend with 30ish mostly carb'd motorcycles runs them on 100LL because it can sit forever. We have no access to non-ethanol gas beyond buying VP T4 for $120/5 gal pail.

Home Depot has high octane no ETOH fuel in the weed wacker section for about 15$ a gallon. That is what I use. Works well in the two strokes as they also sell ETOH free premix in 1:50 and 1:40

wae UltimaDork
6/5/24 4:08 p.m.

I find it bizarre that I'm the guy to say this, but wouldn't it be a really good idea to not add to the number of engines that are sending lead particles out their tailpipes?

APEowner GRM+ Memberand UltraDork
6/5/24 4:14 p.m.

californiamilleghia said:
is AV gas color tinted like "farm" diesel is tinted red ?

It's blue. I use the translucent white fuel jugs and it looks like I've got 20 gallons of washer fluid in my trailer.

BenB HalfDork
6/5/24 5:00 p.m.

Not really race car related, but back in the early 80s, a DC-3 freighter would pass through our FBO fairly regularly to pick up freight. He'd pay for a certain amount of gas in order to get the bulk discount, even though the plane wouldn't take it all, and let all of us flight instructors fill up our cars with the excess. My MGB ran great on 100LL!

David S. Wallens Editorial Director
6/5/24 5:09 p.m.

wae said:
I find it bizarre that I'm the guy to say this, but wouldn't it be a really good idea to not add to the number of engines that are sending lead particles out their tailpipes?

Sort of related, according to the U.S. Energy Information Information Administration, the amount of avgas (a leaded product) sold has been steadily decreasing. As of 2020, U.S. sales/deliveries have fallen to 412,000 gallons per day–so, if my math is right, about 150,380,000 gallons per year.

Here’s the chart for the above link:

But, yes, that seems like a bit of lead emissions in this day and age. I don’t have the numbers for leaded race fuel sales, but I’m guessing it’s not 150m gallons per year.

mfennell HalfDork
6/5/24 5:14 p.m.

wearymicrobe said:
Home Depot has high octane no ETOH fuel in the weed wacker section for about 15$ a gallon. That is what I use. Works well in the two strokes as they also sell ETOH free premix in 1:50 and 1:40

Cheapest I can find at HD is $22/gal in the 2.1 gallon size. VP T4 is cheaper. My RS250 seems to get 20mpg - I'd be buying (and disposing of) a whole lot of cans! I do use the pre-mix in my infrequently used 2 stroke yard equipment.

At the end of the season, I might fill a 5 gallon can with Sunoco 100 Octane unleaded at the track to use to winter prep the bikes. It's cheaper than T4 (IIRC) and I won't have to dispose of the cans.

Cousin_Eddie (Forum Supporter) SuperDork
6/5/24 5:17 p.m.

David S. Wallens said:
wae said:
I find it bizarre that I'm the guy to say this, but wouldn't it be a really good idea to not add to the number of engines that are sending lead particles out their tailpipes?

Sort of related, according to the U.S. Energy Information Information Administration, the amount of avgas (a leaded product) sold has been steadily decreasing. As of 2020, U.S. sales/deliveries have fallen to 412,000 gallons per day–so, if my math is right, about 150,380,000 gallons per year.

Here’s the chart for the above link:

But, yes, that seems like a bit of lead emissions in this day and age. I don’t have the numbers for leaded race fuel sales, but I’m guessing it’s not 150m gallons per year.

Whole bunch of airplanes out there nowadays running auto gas to save money.