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Old 06-09-2012, 02:27 PM   #1
40 Deluxe
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Default Use of avgas?

With various discussions and threads about the use of avgas in our cars, I thought I'd post this link for getting our daily dose of technical knowledge (actually it's not that hard reading and very informative). Avgas is truly a different animal!

http://royalpacificpetro.com/html/te...as_content.htm

Don't stop at the first page; there's more.
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Old 05-01-2020, 07:32 PM   #2
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Default Re: Use of avgas?

I've burned considerable avgas through motor cars including Model A's.
This was because it was available, I used to buy a tanker load at a time.
It gave no extra performance, neither before or after lead content was significantly reduced.
High compression engines may have been different due lead. Many people came with jerry cans to buy it but I think they were just kidding themselves.
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Old 05-01-2020, 08:34 PM   #3
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Default Re: Use of avgas?

Seems like overkill for our low compression engines. Even the highest compression OHV motors should do well with premium pump gas imho.
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Old 05-01-2020, 08:52 PM   #4
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Default Re: Use of avgas?

On a long tour a couple of years ago, I had trouble with the engine pinging. One of the first things I did after checking the timing was to run a tank or two of higher octane fuel. I tried 98 octane whereas the ordinary stuff I use is 91. It made no difference whatsoever, even after I found and rectified the problem.
I bet I know what you're thinking right now - so what was the problem?
It was the Model A #3/4 crossfire. I fitted the new distributor body I carry and all was back to normal.
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Old 05-02-2020, 06:00 AM   #5
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Default Re: Use of avgas?

100 LL fuel, the kind most general aviation planes use, is known for withstanding long term storage. It smells good, too, smells like you are getting ready to go someplace interesting!
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Old 05-02-2020, 06:49 AM   #6
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Default Re: Use of avgas?

The main thing with avgas is the different carbon chain. It won't varnish and/or break down so it stores well.

Aviation engines are low compression and low speed engines. They don't need any fuel issues while in use, you can't just pull over and wait for a service truck if the engine decides to quit running because of poor fuel.

I use to store engines using avgas just to keep the system from varnishing.
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Old 05-02-2020, 06:49 AM   #7
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Unhappy Re: Use of avgas?

Quote:
Originally Posted by Bruce of MN View Post
Seems like overkill for our low compression engines. Even the highest compression OHV motors should do well with premium pump gas imho.
I totally agree. What can we possibly accomplish using a fuel that was never intended for a low compression antique car. Overkill is very appropriate terminology.
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Old 05-02-2020, 07:32 AM   #8
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Default Re: Use of avgas?

I have a friend who uses it in cars he rarely drives for the reason you mentioned.

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The main thing with avgas is the different carbon chain. It won't varnish and/or break down so it stores well.

Aviation engines are low compression and low speed engines. They don't need any fuel issues while in use, you can't just pull over and wait for a service truck if the engine decides to quit running because of poor fuel.

I use to store engines using avgas just to keep the system from varnishing.
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Old 05-02-2020, 08:43 AM   #9
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Default Re: Use of avgas?

Not all aviation engines are low compression. The average aircraft engine is 8.7:1 ratio. I Work on the helicopter engines and one of them is 10:1.

Avgas is expensive due to the chemical make up and cost to refine. Even though it is called 100 Low Lead, it still has a lot of tetra ethyl lead in there. It is way overkill for most auto engines unless they are high compression but it still has a tendency to load the plugs with lead deposits. I get to clean the stuff off every 100 hours. Aircraft plugs are larger so that they have less a tendency to foul to a point where they won't function.

If a person want to use it, I would recommend mixing it with premium Mogas or Mogas with no alcohol of any rating just to make it go farther and further dilute the lead content. It has too much lead for the average auto engine.
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Old 05-02-2020, 08:44 AM   #10
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Default Re: Use of avgas?

The higher the gasoline's octane, the more additives it has so it does not combust cleaner than lower octane gasoline. Aviation gasolines have 104 or higher octane ratings. Tetraethyllead lead is still used in many aviation gasolines. Unless it is free, don't waste your money on expensive aviation gasoline for your Model A.


Have some fun with your Model A by running some of folklore fuels we hear about from the good old days. I ran my Coupe on home heating, alcohol and blends of both with gasoline. The heating oil made a stink, so my buddy Don would ride run behind me! Perhaps 151 Rum will work?
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Old 05-02-2020, 09:08 AM   #11
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Default Re: Use of avgas?

Rotowrench,

In post 9 you say that plugs must be cleaned.

In 1970 with leaded gasoline the method used by some was sandblasting on two stroke dirt bikes.

We found at dealer shops that blasting took the glaze off insulators which required more frequent cleaning.

What is the practice nowadays?

Thanks
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Old 05-02-2020, 11:38 AM   #12
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Default Re: Use of avgas?

I only know of one aviation engine with 10/1 compression. Most I'm familiar with have 7.5 [or so] to 8.5 [or so].

I consider below 10/1 as low compression.

Avgas certainly still contains a lot of lead.

The higher the octane rating, the slower the burn rate.
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Old 05-02-2020, 01:15 PM   #13
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Default Re: Use of avgas?

I use it whenever I can! It’s great, the car runs noticeably better.

AV gas doesn’t have all of the pollution additives, cleaning additives and other things in regular retail automotive fuel. AV gas stores for a long time and the cars don’t vapor lock. That is the benefit of AV gas.

It’s not much more per gallon than automotive fue and the lead content is relatively low. If you can buy it, I’d try it.
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Old 05-02-2020, 01:52 PM   #14
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Default Re: Use of avgas?

Quote:
Originally Posted by Hitman View Post
I use it whenever I can! Itís great, the car runs noticeably better.

AV gas doesnít have all of the pollution additives, cleaning additives and other things in regular retail automotive fuel. AV gas stores for a long time and the cars donít vapor lock. That is the benefit of AV gas.

Itís not much more per gallon than automotive fue and the lead content is relatively low. If you can buy it, Iíd try it.
you say you use it whenever you can, Why not buy it then at your local airport every fill up ?
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Old 05-02-2020, 03:30 PM   #15
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you say you use it whenever you can, Why not buy it then at your local airport every fill up ?
Because, like you, Iím not always near my preferred gas station when I need gas. Airports are difficult to access if you donít show up in an airplane, so coordinating an 8 gallon fill up takes time and effort. If I wanted hundreds of gallons for an airplane, that would be a different story.

Ethanol free gas isnít available at an automotive fuel station within 100 miles of me, but the residential airport is a mile away.
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Old 05-02-2020, 03:46 PM   #16
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Default Re: Use of avgas?

Is it possible to pay road us tax at airports? Was just curious, back in the drag strip days I was told the airport wouldn't sell here because of no road tax on it.
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Old 05-02-2020, 03:46 PM   #17
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Default Re: Use of avgas?

Hallo und guten Abend!

Tetraethyl lead is often only considered as a knocking brake for highly compressed engines.

Leaded fuel also has the great advantage that good emergency lubrication is guaranteed in the very high temperature-related limit lubrication area (piston/cylinder at top dead center, exhaust valve stem, valve seats).

To date, the replacement has not been fully successful!
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Old 05-02-2020, 04:15 PM   #18
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Default Re: Use of avgas?

Quote:
Originally Posted by Hitman View Post
I use it whenever I can! Itís great, the car runs noticeably better.

AV gas doesnít have all of the pollution additives, cleaning additives and other things in regular retail automotive fuel. AV gas stores for a long time and the cars donít vapor lock. That is the benefit of AV gas.

Itís not much more per gallon than automotive fue and the lead content is relatively low. If you can buy it, Iíd try it.




100LL is still over $4/gal in this neck of the woods.
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Old 05-02-2020, 04:39 PM   #19
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Default Re: Use of avgas?

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100LL is still over $4/gal in this neck of the woods.
That's cheap! I had a ...not 100% stock car that wouldn't run well on less than AV gas.
It'd knock all the time on 91. Knock and rattle on acceleration on 98. AV gas was fine.
Still original series engine block though.
Miss that car.
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Old 05-02-2020, 04:43 PM   #20
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Default Re: Use of avgas?

Fundamentally important to its touted storage value is absence of alcohol.
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