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MG Midget and Sprite Technical - Avgas in a Midget

I've started working at a small airport using airport transfers sevenoaks where we sell 100LL avgas and was told the octane rating on this fuel can run up to 104 octane. I've driven my midget on 93 octane unleaded since I got it and wondering if I could do any damage if I gave it a try.
Bud K

I was under the impression that at least the 1275 (and perhaps all) had hardened valve seats and would be ok without the lead. Is this correct? My 1950's cars are ok without lead (high zinc content in the Iron). I have access to 100LL too but I don't think that it would be worth the expense. Also, it is possible that you would have problems with lead fouling of the plugs. My airplane (Lycoming 0-235) has a low compression ratio (6.5:1). All the lead does not get fully vaporized and some of it gets deposited on my lower plugs. Higher compression ratio engines don't have as much problem (but compression ratios like my Midget engine can still get lead problems with 100LL). The avgas that my plane was designed to run on was 80 octane (probably like 87 octane with the scale that is used for cars). 100LL (even though they call it "low lead" has four times more lead than 80 avgas). 100LL is higher in lead than the fuel that our cars ran on when back when they were sold.

To combat the lead fouling problem, each time I fuel up my airplane I add a few ounces per gallon of 100LL of an additive called TCP (now sold by a company called Alcor). This stuff has been around for a long time. It is a top lubricant(as is lead) and a lead scavenger (helps the lead combust).

If I use that every time I fuel up I don't have any problems with lead fouling the plugs (but the way the result of lead fouled plugs is misfiring - bad thing).

R Harvey

According to Rebecca's remarks it appears you COULD damage your engine. But beyond that, if your engine is not tuned for 104 octane, then you would see absolutely no benefit. In fact, if your engine is not tuned for 93 octane (and doesn't have higher performance spec components which would require higher octane), then you're throwing money away.

JM Morris

AvGas has lots of alcohol for deicing and other additives. The alcohol, which is now component in most high altitude automotive gasolines, is hard on brass, especially carburator needles.

I used AvGas as a fuel additive in Ecuador years ago when high octane motor fuel was not available. One gallon to 15 gallons of leaded motor fuel in my Volvo would completely stop the pinging. A full tank of AvGas would actually render less power and a low top speed without major timing adjustment (advance).
Glenn Mallory

100LL (the predominant avgas in the US) does NOT have any alcohol in it. In fact the subset of certified planes that have authorization to run on auto fuel (regular car gas) are prohibited from using car gas with alcohol in it.
We are required to do a test to verify that the alcohol is not present. (bad for rubber parts, corrosion problems, lower performance).

Airplanes that use alcohol for de-icing use an alcohol supply that is not part of the fuel supply.

Other than possibly causing lead fouling, I don't see why avgas would do any real harm to your engine (but it would be a waste of money).

R Harvey

Of course if you were getting the slops from tank drain downs it wouldn't be a waste of money?
Daniel Thirteen-Twelve

They do a sump every morning - it would be free.

Bud K

I guess that would be ok if you filter it (reason for sumping is to catch water and dirt in the bottom of the tank).

R Harvey

Folks,--just a thought,----you are not paying "road tax" when you buy Avgas. Somebody might be upset about not getting $$$. Bob C
chamberlain Bob

Yes. I am sure that it is not legal to use Avgas for the road without paying road tax. Our local airport used to sell 100LL to the race car guys and they used to make them sign a form confirming that it was for off road use (race track). I guess the tax is a road use tax.

R Harvey

This thread was discussed between 06/07/2010 and 10/07/2010

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