Leaded Aviation Fuel?

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seaweed
Posts: 5
Joined: 23 Jun 2022, 10:10
Location: Eastern Shore, MD

Leaded Aviation Fuel?

Post by seaweed »

Any advantage of using leaded aviation fuel in my little 1992 Johnson 3hp motor as opposed to just using regular non-ethanol? I can get both here on the eastern shore of MD, but wondering if it's worth splurging on aviation fuel? I believe it has an octane rating in the high 90's, but don't hold me to that.

Thanks! Before I joined, I absorbed a ton of excellent info from you fellas!

poorthang
Posts: 189
Joined: 05 Feb 2022, 05:12
Location: brockwell, ar

Leaded Aviation Fuel?

Post by poorthang »

no. counter productive. more octane equals slower burn, less power, less efficiency. you dont need lead to lubricate and cushion the valves. run ethanol with stabil or star brite and call it a day as long as it doesnt attack your fuel system. note: if you use the gas in your tank, and use star brite, you will have no trouble. if you take a long time to use a tank full, dont fill the tank as full. the trick is to cycle the fuel in the tank before it goes bad and attacks your plastics and rubber.

seaweed
Posts: 5
Joined: 23 Jun 2022, 10:10
Location: Eastern Shore, MD

Leaded Aviation Fuel?

Post by seaweed »

Thanks. I can get non-ethanol here, and run that....so I'll just keep running that. Appreciate the quick response!

C&K
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Joined: 18 Apr 2021, 12:50
1
Location: Washburn Co, WI

Leaded Aviation Fuel?

Post by C&K »

seaweed wrote: 26 Jun 2022, 20:35 Any advantage of using leaded aviation fuel in my little 1992 Johnson 3hp motor as opposed to just using regular non-ethanol?
No, don't use it. What you will likely get is 100LL, which contains 3x the tetraethyl lead that automotive leaded pump gas used to have. All it will do is foul your spark plugs, it will stick the top ring on the piston and score the cylinder, and you will get a noticeable drop in power without advancing the timing. Remember that piston airplane engines that use it use special aviation oils that cost $10/qt and are formulated to help prevent lead fouling of the top piston ring, and have two spark plugs per cylinder because the mixture in the combustion chamber needs to be lit on both sides to shorten the burn time.

Plus the airport likely won't sell it you anyway unless you own an aircraft because it's illegal to use it in anything but an aircraft engine.

seaweed
Posts: 5
Joined: 23 Jun 2022, 10:10
Location: Eastern Shore, MD

Leaded Aviation Fuel?

Post by seaweed »

I used to use it in my1992 johnson 3 hp up until it got put away for a few seasons. I used it in everything (on the advice of a duh-canic)....but on the airport on kent island, md, you just walk up, set your tanks down, put in a credit card and pump away. Never had anyone tell me otherwise.

overboard
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Joined: 21 Jul 2011, 10:31
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Location: palmerton pa.

Leaded Aviation Fuel?

Post by overboard »

Here in Pa. you can legally pump it into containers for "OFFROAD USE" since it doesn't have a highway tax included in the price. I don't know about boat motors, but I do know that the 100 LL works pretty good in my 427!

poorthang
Posts: 189
Joined: 05 Feb 2022, 05:12
Location: brockwell, ar

Leaded Aviation Fuel?

Post by poorthang »

overboard wrote: 28 Jun 2022, 02:19 Here in Pa. you can legally pump it into containers for "OFFROAD USE" since it doesn't have a highway tax included in the price. I don't know about boat motors, but I do know that the 100 LL works pretty good in my 427!
whats the price per gallon ?

KMixson
Donor
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Location: North Charleston S.C.

Leaded Aviation Fuel?

Post by KMixson »

The only advantage would be your gas would be a pretty shade of blue until you poured in the two cycle oil. That is all.

overboard
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Location: palmerton pa.

Leaded Aviation Fuel?

Post by overboard »

poorthang wrote: 28 Jun 2022, 08:53
overboard wrote: 28 Jun 2022, 02:19 Here in Pa. you can legally pump it into containers for "OFFROAD USE" since it doesn't have a highway tax included in the price. I don't know about boat motors, but I do know that the 100 LL works pretty good in my 427!
whats the price per gallon ?
I haven't bought it in awhile so I don't know, last time I talked to someone about it I think they said it was over $6.00 a gal. If I wanted max performance, with timing advanced, etc., I would probably have to run it all the time, but with the motor tuned back to factory specs. and mostly a garage queen now, I can get away with just running high test pump gas, usually Sunoco. I think when I first put the hi test av gas in the car it was 110 octane, then they dropped it to 100 where it's been for quite a while.

KMixson
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Leaded Aviation Fuel?

Post by KMixson »

The price for Av-Gas(100LL) in my area is almost $7.50 per gallon up to over $10.00 per gallon depending on which airport you go to.

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kdgrills
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Leaded Aviation Fuel?

Post by kdgrills »

FWIW, I just stopped at the park district airport & filled up the boat (ethanol free, 91 octane gas) this afternoon.

Screenshot_20220628-182659_Brave.jpg
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C&K
Posts: 50
Joined: 18 Apr 2021, 12:50
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Location: Washburn Co, WI

Leaded Aviation Fuel?

Post by C&K »

KMixson wrote: 28 Jun 2022, 09:12 The only advantage would be your gas would be a pretty shade of blue until you poured in the two cycle oil. That is all.
It's a bigger difference than that. Avgas is formulated to burn slow with a low vapor pressure to prevent vapor lock at high altitudes. It is formulated for low compression air-cooled engines that need lead for valve seat lubrication, and that run 30 deg BTDC fixed timing with dual magnetos. Air-cooled aircraft piston engines are 1940's technology, and they haven't changed in that amount of time because it is incredibly expensive to get certification for any newer modern engine designs. So you buy a brand new Cessna 172 and the Lycoming IO-360 in that airplane is the same engine that was sold in 1955, and it still has the same 2,000 hr TBO. Which is not too good, considering that most modern automotive engines will run at least 6,000 hrs to overhaul.

Aircraft piston engines are some of the lowest technology engines still in common use, and the only reason 100LL still exists is because there is no replacement for the engines in airplanes that still require it.

100LL is not "good gas" like many think it is. Using the R+M/2 method they use at the pump for automotive gas, 100LL is somewhere between 80-85 octane.

nccatfisher
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Leaded Aviation Fuel?

Post by nccatfisher »

I believe if you check you will find out most 100LL is a minimum of 99 octane. My best friend is a distributor to the local airport here and that is the minimum they have.

C&K
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Joined: 18 Apr 2021, 12:50
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Location: Washburn Co, WI

Leaded Aviation Fuel?

Post by C&K »

There's been lawsuits in California over FBO's selling 100LL because the lead in the engine exhaust settles in the residential neighborhoods close to airports.

https://generalaviationnews.com/2014/12 ... s-lawsuit/

The phase-out of 100LL in general aviation began when I was still flying commercially. Commercial aviation no longer uses piston engines except for some remote areas in Canada and Alaska where commercial single or twin piston airplanes are still used for commuter airlines and remote bush services. So the phase-out only basically affects general aviation for recreational use.

https://www.aopa.org/news-and-media/all ... ls-for-all

C&K
Posts: 50
Joined: 18 Apr 2021, 12:50
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Location: Washburn Co, WI

Leaded Aviation Fuel?

Post by C&K »

nccatfisher wrote: 28 Jun 2022, 22:35 I believe if you check you will find out most 100LL is a minimum of 99 octane. My best friend is a distributor to the local airport here and that is the minimum they have.
Sorry, but totally different rating. Octane is not octane. Octane gets its name from 2,2,4-trimethylpentane, which is an iso-octane. This iso-octane has been assigned the reference value of 100 for testing purposes. The normal heptane (C7H16) molecule is the 0 octane reference fuel.

There is two different ratings, RON, and MON. 100LL uses the RON method. Automotive pump gas uses the RON+MON/2 method, which is the average of motor octane vs research octane. So while they can call 100LL 100 octane for aviation purposes, for automotive purposes it is the equivalent of the "mountain gas" they sell in the western mountain states. Only difference is, it contains a LOT of lead - 3x what the old "ethyl" leaded premium automotive gas used to have in the 60's.

Do not use it in your outboard - it will mechanically damage the engine due to the amount of lead in it. And I'm telling you that as a commercial pilot (now retired) and I also hold a A&P. Been working on aircraft engines for 40 years. The spark plugs in an aviation piston engine barely last 100hrs due to lead fouling. And the ignition systems used on piston aircraft engines are way hotter than what you have on your outboard. They have to be to fire the plugs with all the lead, and we can't abrasive-blast aviation engine spark plugs to clean them - it's illegal. And it costs $270 to put a new set of spark plugs in a typical four-cylinder opposed aircraft engine. If you think boats are expensive, try airplanes.