Thread: Aviation Fuel

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I have 11.5:1 compression and I've been using AV gas 100 octane in it for years. Last week someone told me that it has air mixed into the fuel for high altitude motors as in airplanes and that this mixture is not so good for car engines. Apperently it leans them out and even causes predetination. He suggested using 94 octane with 108 octane booster mixed in it. Is there any merit to this?

Assuming that you have been watching your plugs all this time and havent seen anything strange (like aluminum on the insulators), there is nothing wrong with AvGas (except that it is illegal to run gas that is untaxed here in the US).

Anyway, if an airplane is at low altitude, how does it keep from screwing up the engine? AvGas does not have air added to it....someone is blowing air up your tailpipe!!!

AvGas may have additives to change it's vapor pressure, etc. Have you also checked the price for race gas in your area? The last barrel that I bought was about $4.25 a gallon....not bad for the good stuff.

mike in tucson

In general AVgas will result in a lean condition. Air planes are all able to adjust mixture on the fly. For take-off for instance they richen it all the way up and cruising at higher alts they can lean it down. AVGas also is high in lead and will kill a converter and some O2 sensors may not work with it. I believe its stoichmetric ratio is a bit different meaning that the carb might need to be tuned. It also has several other additives in general that a car doesn't need but I don't think they hurt anything. I would be wary of rubber hoses etc until you get used to it.

Like Robot says though, you could keep an eye on the plug readings and try it out.

Kitz

Originally Posted by robot

Assuming that you have been watching your plugs all this time and havent seen anything strange (like aluminum on the insulators), there is nothing wrong with AvGas (except that it is illegal to run gas that is untaxed here in the US).

Anyway, if an airplane is at low altitude, how does it keep from screwing up the engine? AvGas does not have air added to it....someone is blowing air up your tailpipe!!!

AvGas may have additives to change it's vapor pressure, etc. Have you also checked the price for race gas in your area? The last barrel that I bought was about $4.25 a gallon....not bad for the good stuff.

mike in tucson

Thanks for responding Mike, I am in the process of building me a shop, and once I have that built, I will look into buying race fuel by the barrel.

My plugs are always fine. Last fill up I paid $1.68 per litre. A liter is near the same size as a US quart.

I'm not so sure 100 octane fuel is available any longer. It was replaced a few years back with 100 LL, which is the Low Lead variety. 80, which was tinted red, has all but gone the way of the Dodo bird. 100 LL is tinted green. There was a blue and a purple that had higher octane ratings. There is no air entrainment (sp) involved, as you gain altitude you can manually change the fuel mixture as required. Sniper

I don't know what the blue is, but I remember the purple as being 115/145 from many years ago. (recip fighter plane fuel).

i used the 100LL for many years. pistons still have tops on them

Blue used to be 108/135, but I just checked on this and things have changed. Apparently Avgas 100 is still available, and it's still green, while the Avgas 100 LL is now blue. I haven't flown for a while, (5 years this coming Aug.) and the last 12 years of that was in a homebuilt that I had built. Since I used a converted automotive engine, I could legally use auto fuel, which I did. Things change I guess. Sniper

yep all the stuff i used was dark blue to purple there is no dot or road tax on it that is the big deal i guess

I've seen others who had problems with flex lines and rubber type products break down over time causing expensive repairs. Another problem is the high lead content. 100LL has about 4 times the lead that leaded automotive fuel had. This can cause fouled plugs, O2 sensor and catalytic converter failure. Not to mention the oil contamination and sludge build up that occurs over time. General aviation is very antiquated. If it was cost effective all those gas motors would run on some version of 80UL. And last but not least, avgas is very expensive.

AirNav: Local Fuel Prices

Avgas - Wikipedia, the free encyclopedia

cars i used it in cars that had no O2 or cats never had any oil sluge they were very hi cr bbc and like the lead but yes if you have any of that stuff it would not be good or if you think you need hi test fuel for a car thats low cr will not work good

I used AvGas in my Vette for years. However, I used a 50/50 mix with premium. I ran a roller cammed bbc with a dominator and 11 1/2 compression on nitrous with no problems.