Technical Aviation fuel, should I be using it?

Lately I've been using av-gas in both hot rods when I could get it. Both are mild Chevy 350's. Also use it at times in my '76 KZ-900. I've never asked the attendant about octane or lead content and I assume it has no ethanol, but not sure. Usually they are quite busy at the little airfield where I get it and I'm always reluctant to tie them up asking a bunch of questions. Not only that, but I feel a bit guilty getting a 5 gallon can of fuel when they are trying to fuel up aircraft. My questions to you fellow hot rodders: What is typical octane rating for small aircraft use around the country? Does this fuel have lead or ethanol in it typically? I just picked up 5 gallons this morning at $7/ gallon which I don't feel is too bad all things considered...Thanks for any responses.

20230827_092724 by lothiandon1940 posted Nov 14, 2023 at 10:05 AM

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I ran 100LL av gas in a dirt modified, SBC with 12.5 CR with no problems. 100LL was a avgas with a lower lead content and was a light blue color. Back then all avgas had lead in it(1980’s). There might be Nolead avgas now-not sure. I do know that the local airfield where I used to buy it won’t sell to anyone walking in with a gas can. Airplanes only.

 

100LL and 100ULL are still used the most and is dyed blue. 100 octane low lead or ultra-low lead. New lead-free formulations are out and dyed green.

 

I'm not sure why you would need Av gas for a mild 350 for street driving but to each his own if it makes you happy. The only guys I know who run it are some racers who are running some serious compression in their race cars or a few street rods with high compression engines. More octane demand than what non ethanal pump gas has as we don't have stations that stock VP race gas locally that I know of.

Truthfully I couldn't go anywhere worth going to and back on 5 gallons no matter where I bought it Simply because of distances. The local Conoco sells non ethanal premium as do a few other stations in this area. I use it in my lawn mower and boat but don't run it in my street rigs. I don't have anything with a carb old enough to need it but that may change when I get the flathead going.

You can find Non Ethanal in MD using this site. https://www.pure-gas.org/ Actually it can be used in any state and Canada.

 

I have a Newley built pretty aggressive 355 SBC in my 55 BelAir. I tried 91 non ethanol and had a few issues with slight pinging and an occasional slight dieseling at shut off. Timing was not the issue, so changed to 100LL av fuel and it cured everything. I can get the fuel at my local airport here in Missouri for $5.15/gal, so that is all I use in the 55. I suppose I could mix the 91 & av fuel but don’t see the need as the price difference isn’t that great.

 

If nothing else it smells good! If you still have a place that will sell it to you in a can you are fortunate.

I don't know how things around you but a lot of places are beginning to Crack down on cars on the road with fuel that was not purchased at a gas station because of the road tax not being paid. A lot of farming communities have had this issue but mostly with the diesel since big farms get their fuel delivered as AG Fuel and its dyed red, as mentioned the AV Fuel is dyed blue. If they dip your tank and the cop is a dick they can tow your car.

 

Aviation fuel has a much longer shelf life than street gas. It does have lead in it and it does not have any road tax at the pump. Not paying road tax is, well, you get it.

 

I don’t think you need AV gas, some say lead is needed for older non hardened valve seats but I’ve run a couple older engines on no lead without any bad effects. Like Mark says AV gas doesn’t seem to evaporate or go bad, maybe use AV gas when putting cars up for the winter. I wouldn’t worry about using no lead no alcohol premium fuel.
Dan

 

If I hardly ever drove my cars, I might consider using something exotic (meaning something I can't get at the gas station down the street). But I drive them, so I use normal pump gas.

 

Can you, yes. Just like pump gas, the higher the octain the slower the burn happens in the cylinder.

 

Way back, used to use AV gas, as a base when mixing race fuel. We added Tolulene, it worked pretty well.
Lots of compression, lots of advance, lots of rpm. Lots of people thought the motor was "big".
Used to pull away from the big buck cars, going up hill. No, it wasn't legal, but they never checked.
Back then, you couldn't buy fancy "race gas", like you can now. In the case of the OP, extra octane
does not make more power. Some dyno tests, suggest more octane than you need will cost power.

 

If your engine has 10-10.5 cr there’s really no point. If you do decide I would blend with pump gas. Maybe 3 or 4 to 1 ratio?

 

I have found that mixing 101 ll Av Gas with 91 octane out of the pump stopped vapor lock when nothing else would. 3 gallons Av Gas to 15 gallons of 91 octane did it, and, exhaust smelled great.

 

I have no clue what the octane is on avgas these days. I used to get 5 gallons of avgas from the helicopters when i was on watch in California. I would open a petcock and time it for 20 minutes making sure the range patrol would find me a long distance from the copter i had set the gas can by. It was 115/145 octane and would be good fuel for the b dragsters we took to Bakersfield. Got caught fueling the dragster one time by the protest guy. Told him it was Mohawk Supreme when he noticed the purple color. he said ok man, and walked away. Good times back then. Once we had no money for gas and had to get back to the base, so no choice but to dump the avgas into my 60 chevy tow car. Tailpipes were white when we got to the base, but didnt harm the 283. Got lucky i suppose

 

Thanks for all of the input everyone. Much appreciated. I guess my thoughts were, if one of the vehicles sits for a month or two hopefully the av-gas won't deteriorate like ethanol blended fuels might.

 

My 100% gas here in Tennessee means my stuff I don't drive often will start just fine after sitting for months. My mower starts 2nd pull every spring, it's 25 years old and only uses 100%.

 

...By 100% do you mean NO ethanol?

 

I would also think AV Gas wouldnt boil in the fuel bowls, like we see happining more and more often with the pump gas available today.

Bill

 

If you have a Dynamic Compression Ratio of about 8:1 (or lower), you don't need av gas. UEM Pistons has an online compression calculator for both static and dynamic compression ratios.

 

I use 91 octane ethanol free premium car gas with a lead additive in my airplane , 180 hp lycoming

 

Pump gas absolutely sucks these days, even non ethanol. The first 1.5 gals will be 87 or 89 octane unless the guy before used 91 or 93. If there are dedicated hoses going to each handle you will get what you pay for, however if all fuel gets dispersed through one hose, which is common these days, you won’t get all premium.

 

Yes, 100% means no ethanol. We have 2 places in town that sell it. I see muscle cars, vintage cars, high performance bikes at these stations all the time.

 

Sta-bil Fuel Stabilizer does what you want, easier and less expensive.
https://www.sta-bil.com/

 

I run unleaded premium with no alcohol in my old cars and it seems to help them start after sitting and doesn't harm the fuel system. I had problems with fuel pumps on my 60 Thunderbird running gas with alcohol and changed then.

 

Is there any downside to using it? (Other than the price)...Does it mix OK with premium pump gas? I'm never running straight av-gas (couldn't afford it!). Just curious if running it has any detrimental effect other than lightening my wallet.

 

You must have more disposable income than I do. I put Rec gas (no ethanol) in the roadster in Florida, it was 90 cents more per gallon. The little DeSoto Hemi is 7.5:1 compression, it ran no differently. I was at WaWa one day to get gas, they were out of Rec fuel so I put Regular 87 in it and haven't looked back.
My '34 had a stout 283 that was supposedly 10.5:1, it was happy on regular unleaded.
If you're simply concerned about 10% ethanol gas setting and damaging your fuel pump and carb, just find a station that sells Rec fuel. Here in Michigan it's the same octane rating as premium, it's almost a buck more than Regular but WAY less than $7 a gallon.

 

What lead additive do use, is it lead or a substitute?
Dan

 

Yes, you can mix it with premium pump gas. Since you said you have two mild 350's, I'm assuming they're 9.5:1 or less compression. If that's a correct assumption, there's really no reason or benefit to run Av gas just to avoid ethanol content.

If you're worried about storage, throw in some stabilizer before you store it for several months at a time. Otherwise, just run pump gas.

We used to run Av gas mixed with premium in former race snowmobiles that we used for ditch banging. That was only because the compression ratio needed higher octane. The annoyance and cost of getting Av gas just to avoid some ethanol doesn't make much sense to me.

I run 87 Octane in my mild 350's, they sit a lot and I've had zero issues with regular pump gas. High compression and high octane sounds fun, but with questionable fuel quality in small towns on road trips, everything I own needs to be able to run on 87.