Why not Avgas in your car?

This isn’t a new idea: Why not run aviation fuel in your classic? Thanks to its high octane and lack of ethanol, this avgas sounds intriguing.

High Octane:

Pump fuel intended for cars and trucks is rated on the Anti-Knock Index, which is the average between the Research Octane Number and the Motor Octane Number. Avgas, however, is rated on a slightly different scale. As a result, the avgas 100 found at many regional airports would have about as much knock resistance as a 105-octane fuel intended for cars and truck

Highly Refined:

Zachary J. Santner, technical specialist at Sunoco Race Fuels, notes that avgas can be more refined and consistent than the fuel found at the corner store. Vapor pressure for avgas, he explains, often falls between just 5.5 and 7.1 psi; depending on the season and location, typical pump fuel for passenger cars can range from 5 to 15 psi. However, Santner adds that his company’s race products never deviate, always following the same formula.

Zero Ethanol:

Avgas doesn’t contain any ethanol. While ethanol can help gasoline make more power, it can also cause hardware issues in older vehicles. “Can’t pull your plane over on the side of the road if there’s a problem with the fuel system,” Santner notes.

Some Lead:

Not only does lead cause smog, but it’s not compatible with the oxygen sensors and other pieces of emissions equipment found in most cars built since the ’70s. Even avgas 100LL, a newer, low-lead option, still contains lead–about 1.9 grams per gallon.

Legality and Logistics:

Avgas isn’t taxed for road use, and cars might not be welcome on the taxiways at the local airport.

Unnecessary Additives:

Avgas contains some of the same additives found in pump fuel, including corrosion inhibitors and antioxidants that increase shelf life. However, some of its additives aren’t found in car fuels–like compounds that prevent icing and static electricity. “It’s just more additives that you don’t need,” Santner notes. “Car gas has additives designed for cars, and airplane gas has additives designed for airplanes.”

More like this

Comments

aircooled MegaDork
1/6/21 4:05 p.m.

Summary:

If you have a cat or an oxygen sensor on your car = maybe bad idea

If you don't = very good idea (other than the legalities / emissions of course) if your car can use the octane.

One aspect not covered is that Avgas is FAR more stable then road gas. I had 100LL in my Ghia for many years, and it does not turn to turpentine like road gas does (at least not nearly as fast). If I had the option to put Avgas in my car, I certainly would. But of course, it's pretty much an aviation engine anyway.

Brian_13 New Reader
1/6/21 5:09 p.m.

Using leaded fuel is illegal on the road (and should be illegal everywhere) and irresponsible. The rest of the discussion is pointless, except to mention (as the article failed to) that unleaded racing fuel addresses any legitimate fuel needs for classic and competition vehicles.

TorqueNRecoil
1/6/21 7:21 p.m.

Brian, lighten up. Classic cars are hardly driven. Same for drag cars. They go 1/4 mile at a time, and some only 1/8 mile. Your comment "should be illegal everywhere" is (as you yourself said) is irresponsible. You can't just put whatever you want into the tank of an airplane. If your Lycoming or Continental was certificated for 100LL, and you put in some ethanol-laced unleaded auto gas, burn a piston or valve, crash and kill somebody, you wil be sued. If you survive the crash, you will lose the lawsuit. The very first thing the NTSB does when they inspect a crash site, is to check the fuel tanks.

Brian_13 New Reader
1/11/21 1:29 p.m.

TorqueNRecoil said:
... Your comment "should be illegal everywhere" is (as you yourself said) is irresponsible. You can't just put whatever you want into the tank of an airplane. If your Lycoming or Continental was certificated for 100LL, and you put in some ethanol-laced unleaded auto gas, burn a piston or valve, crash and kill somebody, you wil be sued. If you survive the crash, you will lose the lawsuit. The very first thing the NTSB does when they inspect a crash site, is to check the fuel tanks.

I didn't suggest putting auto fuel - especially with ethanol - in an aircraft. Unleaded aviation gasoline is readily available, there are certified aviation engines to use it, and the general aviation industry has had decades to adapt to fuel without lead. Aircraft are operated for a very long time, but piston engines need rebuilds every few hundred operating hours so every one out there has been rebuilt since the 1970's and they could all be safely and reliably running unleaded. There is no excuse.

Brian_13 New Reader
1/11/21 1:38 p.m.

TorqueNRecoil said:
Brian, lighten up. Classic cars are hardly driven. Same for drag cars. They go 1/4 mile at a time, and some only 1/8 mile.

That's like saying that I only drive on a highway one in a while, and there's only one of me, so none of the rules of the road should apply to me... after all, what effect could just my one car have? The fact that both classic road cars and any competition vehicle are completely unnecessary - just hobbies and entertainment - means that they have less excuse than real working vehicles for pollution. And if Formula 1 can run on unleaded gasoline (which it does), your obsolete drag car burning leaded gas looks almost as antiquated as a coal-fired steam engine.

aircooled MegaDork
1/11/21 2:02 p.m.

Brian_13 said:
Aircraft are operated for a very long time, but piston engines need rebuilds every few hundred operating hours ...

The most popular general avation engine for many many years is the Lycoming 0-360. It has a recommended TBO (time between overhaul) of 1500 hours (I know someone who pushed his, with careful monitoring, over 2000). A rebuild is about $16,000. Most general aviation planes are not used that much. It can take a LONG time to run a 360 out.

Now, a Merlin engine (P51), which is definitely a high strung engine, TBO is 240 hours, (rebuild $60,000+).

Tom1200 SuperDork
1/11/21 3:57 p.m.

I just buy the 100 octane unleaded race gas for my vintage race car. This has way less ethanol the other pump fuels. Driving to the airport to fill up seems like a pain.

Curtis73 (Forum Supporter) MegaDork
1/12/21 10:46 a.m.

Avgas also has a higher vapor pressure and lower BTU content

o2bdriving
5/3/21 8:04 a.m.

I store my car with 100LL and drive it with E10 pump gas. Would use E0 for both if it were available locally. Besides the environment, my AFR sensor doesn't like lead.

wspohn SuperDork
5/7/21 1:49 p.m.

We had one idiot that paid for avgas in his 60s Corvette. Of course he got zip as far as any additional power - it had ignition with mechanical advance and adding higher octane fuel without increasing advance can actually yield lower output. I guess it got him some bragging rights among his equally dim-witted friends ("Wow - jet fuel!" - wrong of course. If he'd wanted jet fuel - kerosene - it wouldn't have run at all).