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Old 05-17-2019, 04:48 PM
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Default Aviation Gas

Does or any have run Aviation gas in their Cobra? I have a older Backdraft with 4,500 miles with a Ford Crate 392 Race Engine that is rated at 430 HP. Not going for performance but rather running decent gas vs. 93 octane with 10% or less ethanol that craps out carburetors.

There is a small airport near the house that will sell Aviation fuel rated at 100 octane and no ethanol for $4.50 a gallon if you bring your own fuel cell (which I have).

I would imagine there should be no damage on the car since there are no catalytic converters.

If you have ran Aviation gas, appreciate you letting me know of your experience. And if you know of any reason not to run the gas, let me that too.

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Old 05-17-2019, 05:15 PM
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What does your engine builder specify as the recommended octane rating? Unless your car is tuned for the higher octane you will not get any benefit.
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Old 05-17-2019, 05:44 PM
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I never ran aviation fuel. Seems I heard someone warn against it once, but cannot remember why. I honestly cannot think of a reason why it would be unsafe to run in an automotive engine.

A friend has an airplane. On it's last rebuild the mechanic talked him into a higher compression ratio piston. There are two versions of his engine sold from the factory with the two different compression ratios. Seems like his was 11:1 or 12:1 and the pistons they put in were 13:1 or 14:1. The fuel could handle that much compression. Gave him more Hp, but it also uses quite a bit less fuel. He is very happy he did it. The only point to the story is just how much compression this type of fuel can handle. More Octane than your engine needs.

You can also buy race fuel that has no ethanol.

The biggest issue with ethanol corroding your carb, is when the car sets over the winter for months. It sucks water out of the air until there is enough to separate. If you ran a couple of tanks of ethanol free gasoline before storing for winter and added a good stabilizer (I like seafoam), I think you wouldn't have near the problems, if at all.
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Old 05-17-2019, 06:06 PM
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Read this:

https://www.fuelexpert.co.za/canirunavgas.php

Apparently the government gets upset, as this fuel has no road taxes. It would be no different than running farm diesel fuel on the highway, which they will hammer you for.

They claim the amount of lead is too high and screws up valves and guides. I'm not sure I buy that, as aviation engines have valves too. On the other hand, air plane engines spend most of their time operating at high Hp levels, and it may burn cleaner, as a result. So, it may be true.

They also claim the lack of light hydrocarbons makes cold starts harder and it does not respond to quick throttle changes well. True airplanes run steady most of the time. Not a lot of throttle changes running through gears. The high compression in aviation engines would allow them to cold start better, but you're not going to start a Cobra in the winter.

They also said the fuel is more dense and would need jet changes. That might be true. Most people are not going to want to use a good wide band O2 to tune it as the lead will trash their O2.

Last edited by olddog; 05-17-2019 at 06:11 PM..
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Old 05-17-2019, 06:22 PM
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You should be fine running the 100LL. I've used it in several cars (including my BDR) with no ill effects. Smells good too.
Much cheaper than Race fuel which can easily run over $12 per gal depending on the octane rating or if unleaded.
You don't really need it with a street crate motor under 11:1.
But this site will help you locate Ethanol free gas stations in your state.
https://www.pure-gas.org/
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Old 05-18-2019, 04:46 AM
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Here's an abbreviated version of the link posted by OLDDOG.

AvGas 100LL or "100 Octane Low Lead "
TEL (Tetra-ethyl-lead) is added to raise the octane. When used in a motor vehicle this fuel will leave a lot of lead deposits in the motor. 100LL has a high lead content (0.5 grams per litre), even higher than leaded race fuels.
The deposits left when TEL(lead) is burned are corrosive and damaging to valves, valve guides, valve seats and cylinder heads. Lead deposits will also block oxygen sensors and foul spark plugs even after only a short use.
100LL has a chemical package for performance at high altitude, not the best thing for motor vehicle performance at ground level.
AvGas is blended for large-bore, long-stroke, low RPM engines at high altitude.
AvGas' higher octane is useful but smaller-bore, shorter-stroke, high RPM engines will perform better on racing fuel or quality octane boosters.
AvGas has lower volatility so when 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 best engine performance.
100LL is blended with a high percentage of aromatics causing reduced throttle response which is not an issue with an aircraft engine but certainly an issue in a high-performance automotive engine.
These high levels of aromatics will also damage rubber components in automotive fuel systems such as fuel lines, fuel pump seals and injector washers.
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Last edited by Unique427; 05-18-2019 at 05:01 AM..
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Old 05-18-2019, 05:16 AM
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Depending on where you live, you can usually find Sunoco Race Fuel anywhere. Unleaded street legal versions and leaded race versions.

https://www.sunocoracefuels.com/fuel-finder
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Old 05-18-2019, 05:31 AM
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In Michigan, my current favorite option is a mixture of what is sold as “Recreation Gas”, which is non ethanol 90 octane sold for jet skis, boats, off road buggies, etc. I mix in 1/3 race gas available at the same station which is 100 octane, non ethanol, high lead. The extra lead kicks up the octane mix. My Cobra, CSX2367, is a standard 289 hipo that knocks on “normal” fuel. We have several other collector vehicles that seem very sensitive to ethanol, in particular getting vapor lock with ethanol so the $4/gal recreation gas, which includes road tax, is a nice solution.
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Old 05-18-2019, 06:04 AM
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Quote:
Originally Posted by Unique427 View Post
Here's an abbreviated version of the link posted by OLDDOG.

AvGas 100LL or "100 Octane Low Lead "
TEL (Tetra-ethyl-lead) is added to raise the octane. When used in a motor vehicle this fuel will leave a lot of lead deposits in the motor. 100LL has a high lead content (0.5 grams per litre), even higher than leaded race fuels. (100LL has 2.12 grams per gal, Race fuel avg 2-5 grams per gal depending on the octane they are achieving)
The deposits left when TEL(lead) is burned are corrosive and damaging to valves, valve guides, valve seats and cylinder heads. Lead deposits will also block oxygen sensors and foul spark plugs even after only a short use.
100LL has a chemical package for performance at high altitude, not the best thing for motor vehicle performance at ground level.
AvGas is blended for large-bore, long-stroke, low RPM engines at high altitude.
AvGas' higher octane is useful but smaller-bore, shorter-stroke, high RPM engines will perform better on racing fuel or quality octane boosters.
AvGas has lower volatility so when 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 best engine performance.
100LL is blended with a high percentage of aromatics causing reduced throttle response which is not an issue with an aircraft engine but certainly an issue in a high-performance automotive engine. (can cause part throttle response issues)
These high levels of aromatics will also damage rubber components in automotive fuel systems such as fuel lines, fuel pump seals and injector washers. (This applies to all gasoline and to a greater extent Ethanol mixes)
There are a couple of partially correct statements in the above from the "Fuel Expert" website in South Africa. Correct are in Bold, additions are in Italics underlined, Incorrect sections I left alone.
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Old 05-18-2019, 08:56 AM
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Look for the highest octane (non ethanol) fuel in your area and if need be add a reputable octane booster or a blend of race gas. My CSX with a FE 427 runs great on just 93 (non ethanol) while the dedicated track Shelby GT350 uses 110 race gas.
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Old 05-18-2019, 09:29 AM
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I had good results with AV gas in my first Cobra. 496 Chevy 11 to 1 engine/ alum. heads. I'd add one ounce of Marvel Mystery Oil, per gallon and had good results, even when using a 100 hp dose of nitrous. I'd read that the MMO helped lubricate the valves when running AV gas. My 2. BTW, smelled great and turned the insides of the exhaust exit nice light grey. Just like de ole daze.
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Last edited by Karl Bebout; 05-18-2019 at 09:31 AM..
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Old 05-18-2019, 10:04 AM
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Default Aviation Gas

Thanks for the input. From additional research, it looks like there is too much lead in Aviation gas that would not be good for a modern built engine. The added octane would be nice and most high performance engines would love it but the lead over a period of time would do damage to valves and valve stems and guess carbon up the pistons.

Will back a trip to Buc-ees in Texas and fill up when possible on their ethanol free gasoline.

Once again, thanks for the feed back.
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Old 05-18-2019, 10:54 AM
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Aviation gas in my 289 ERA Cobra allows the motor to run extremely well. In addition longtime storage (long Vermont winters) is not a problem.






John

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Old 05-19-2019, 03:09 AM
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I can get alcohol free 90 octane locally. about $4/ gal. Works well in my car which has about 10 to one compression.
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Old 05-19-2019, 06:00 AM
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When I was in Hawaii where the gas stated as 92 octane might be 89 octane at
best, I found that adding about 1 gallon of 110 avgas per 10 gallons of the 92
premium made the 351 run much smoother in high gears (while driving up H-3
freeway to get to Kailua) at lower rpm's. When I shipped it to Texas it runs about
the same here with the 93 octane as it did with the avgas there. At $6/gallon it
was a cheaper option for better performance - and yes, it did smell great!
No need it here in Texas.
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Old 05-19-2019, 01:00 PM
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Just got back from autocross test and tune. Burned up 5.5 gallons in eight runs....about kilometer per run. So looks like about five gallons per mile.
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Old 05-19-2019, 04:13 PM
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Isn't 5.5 gallons in 5 +- miles about 1 mile per gallon?
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Old 05-19-2019, 07:22 PM
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Quote:
Originally Posted by HI Cobra View Post
Isn't 5.5 gallons in 5 +- miles about 1 mile per gallon?
Dang, you caught me!
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Old 05-20-2019, 07:50 AM
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Quote:
Originally Posted by Karl Bebout View Post
I had good results with AV gas in my first Cobra. 496 Chevy 11 to 1 engine/ alum. heads. I'd add one ounce of Marvel Mystery Oil, per gallon and had good results, even when using a 100 hp dose of nitrous. I'd read that the MMO helped lubricate the valves when running AV gas. My 2. BTW, smelled great and turned the insides of the exhaust exit nice light grey. Just like de ole daze.
You said light grey? I would pull my plugs,sounds like you are melting your pistons. The plugs should be tan like the skid marks on your underwheare after driving a cobra with 600hp!
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Old 05-20-2019, 09:37 AM
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I've run a mixture of Av gas and 91 0ctane in my 482 bb for some time. Never had a problem, untill. Recently I put 10 gallons of av gas with only about two gallons of 91 octane. Car began running really bad like it was flooding. Problem. Av gas is designed to be run at altitude, thus it has a higher density. If you dont adjust the floats running a high percentage of
av gas, you will have this problem. Once it got mixed with 91 again the car ran perfect.
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