Airplane Fuel in 1970

[Kurt G.]

Re: Airplane Fuel in 1970

One other thing Mike didn't mention about Avgas (100LL) is that it is a very dry fuel. What the big difference is between Avgas and pump gas is that Avgas comes off the cracking tower at a higher level/temperature which "removes" some of the oil from the finished product. It also has all the stuff that burns (benzine, butane, propane, etc) left in it. Plus it has some lead left in it for top cylinder lubrication. But don't be fooled, in a automotive engine that isn't designed to burn this stuff your problem won't be pinging, it'll be the holes it will burn in you pistons. It burns much hotter.

[Duke W.]

Re: Airplane Fuel in 1970

But don't be fooled, in a automotive engine that isn't designed to burn this stuff your problem won't be pinging, it'll be the holes it will burn in you pistons. It burns much hotter.

I don't recall hearing this myth before, but that's what it is. For the broad range of typical hydrocarbon fuels that can be consumed by spark ignition engines, maximum flame temperature with optimal spark advance is about 4500 degrees F. That's everything from natural gas (methane) to nearly any blend of hydrocarbons that can be legitimently be called "gasoline".

Holes in pistons and burned valves are caused by detonation. The detonation shock waves increase heat transfer to the combustion chamber boundaries by about an order of magnitude, so sustained detonation can rapidly overhead pistons and exhaust valves that are already operating relatively close to their thermal limit. I covered this in my San Diego presentation, a link to which is in post #7.

100 LL has a MON of 100 which is a PON of 104-105. So it has much higher detonation resistence than the highest octane mogas other than specialized race gas. In the very few cases where vintage Corvette engines experience detonation on modern pump gasoline that cannot be cured by minor spark advance map changes, a 25 percent blend of 100LL avgas in pump premium will usually quell any detonation.

Duke

[Bill L.]

Re: Airplane Fuel in 1970

I have a 70 350/350 which has never been apart. I can say without a doubt that it runs WAAAY better with higher octane racing fuel. I generally go with 40/60 mix with 110 octane and regular gas. It idles better and runs better through all RPMs. Can I tune it to run decent on pump gas? Absolutely. It just does not run nearly as well. This is with a perfectly tuned carb, distributor, etc...

I am lucky that I can get high octane unleaded racing fuel a couple miles from the house.

Bill

[Joe C.]

Re: Airplane Fuel in 1970

What are the thoughts on cars that don't get driven much, does AV fuel have less issues with varnishing?

Three years ago I revived a 1992 Honda Accord that belonged to an elderly aunt, and had not been driven since 1996. It sat in her deteriorating and collapsing garage with the windows tightly closed for all those years. The 18,000 mile car had cats and other creatures living in the spaces between the floorpan and the chassis components, in the engine compartment, and above the muffler. The interior was pristine and had the strong aroma of fresh vinyl, carpeting and upholstery.

As the temperature was in the teens on the crisp January day that I drove it home, and I was unsuccessful in siphoning the gas out of the 1/2 full tank, I did the next best thing. I added 2 cans of "dry-gas", removed and cleaned the 4 injectors, changed the fuel filter and hoped for the best. After replacing the battery and filling the four flat tires to 32 psi, I shot some ether into the plenum, pulled the plugs and shot some oil into each cylinder, removed the coil wire and cranked it for about 10 seconds until fuel appeared at the fuel filter, replaced the plugs and coil wire. It fired up almost immediately and ran without a hiccup. Filled up with gas at the first station I passed on the way home. Drove the car until tank was near empty, and filled it twice more and added 2 cans dry-gas to each of the next two fill-ups. Replaced the fuel filter after the third tankful of gas. The car ran flawlessly until I sold it last month with 68,000 miles on the clock.

[Clem Z.]

Re: Airplane Fuel in 1970

i think one of the problems with ethanol in the gas is the rules say up to 10% and the ethanol is dumped into the tank trucks at the bulk plant and i often wonder how accurately they do this. back in the day before race gas all dyno testing on race engines was done with avgas because every barrel was the same because of the govt specs and i am sure this is true today.

[Joe C.]

Re: Airplane Fuel in 1970

i think one of the problems with ethanol in the gas is the rules say up to 10% and the ethanol is dumped into the tank trucks at the bulk plant and i often wonder how accurately they do this. back in the day before race gas all dyno testing on race engines was done with avgas because every barrel was the same because of the govt specs and i am sure this is true today.

The government specs should apply to E10 as well. There shall be "no more than 10% ethanol, by volume" in E10 mogas.

[Clem Z.]

Re: Airplane Fuel in 1970

The government specs should apply to E10 as well. There shall be "no more than 10% ethanol, by volume" in E10 mogas.

all the pumps around here say "may contain up to 10% ethanol"

[Joe C.]

Re: Airplane Fuel in 1970

all the pumps around here say "may contain up to 10% ethanol"

Clem,
The pump verbiage is repeating the law's verbiage................without the legalese.
Joe

[Michael W.]

Re: Airplane Fuel in 1970

One other thing Mike didn't mention about Avgas (100LL) is that it is a very dry fuel. What the big difference is between Avgas and pump gas is that Avgas comes off the cracking tower at a higher level/temperature which "removes" some of the oil from the finished product. It also has all the stuff that burns (benzine, butane, propane, etc) left in it. Plus it has some lead left in it for top cylinder lubrication. But don't be fooled, in a automotive engine that isn't designed to burn this stuff your problem won't be pinging, it'll be the holes it will burn in you pistons. It burns much hotter.

I don't recall hearing this myth before, but that's what it is.

Duke

After 31 years in the aviation engine business working at an major OEM- if I had a dime for every time I've heard this myth and it's siblings I could almost afford a tankful of the fancy racin' gas or airplace gas people go on and on about.