Avgas 100LL
 

Local airport is selling the avgas at around $3 per gal. Any reason I shouldn't use it with my 65 L79? Been paying around $2.50 for premium unleaded. Engine rebuilt 7k miles ago. Runs great! Yeah, I know why pay $.50 more per gal if it's running good? Sort've want to see how it runs with higher octane. Appreciate your input. Thanks in advance.

Pretty sure your L79 engine will run just fine on 91 octane E10. I see no benefit of Avgas. Others may have a different opinion.

If your car 'sits' for any periods of time and the 91 octane has ethanol, I'd definitely go for the Avgas.

I'm suitably envious. Yesterday here in the People's Republik of Kalifornia I paid $4.09 for E10.

It won't 'run' any different on higher octane..
If it's not pinging (pre-detonation) on premium, you have enough octane in the fuel.

Now, lead for lubricating/cooling the valve seats is a separate issue.. and hotly debated around here!

I run a tankful of leaded through the car every 4-5 tanks for this purpose.
Opinions will vary.

After reading some old posts, looks like the subject has been well covered. At least I know I'll not be hurting the car. Thanks guys.

Some old aviators will claim the aroma of that 100LL will take them back to a simpler time... in the Wild Blue Yonder...

GUSTO

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Originally Posted by jim lockwood (Post 1599233663)

I'm suitably envious. Yesterday here in the People's Republik of Kalifornia I paid $4.09 for E10.

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Yup, me too. I have a 28 gallon tank and filled up on the weekend and it cost me over $100. First time that has happened in a long time.

May have to stop punching it at every light and conserve fuel....well maybe not! :yesnod:

I'm not that smart on Avgas, but my airplane mechanic buddy told me that AvGas is formulated for high altitudes.

Best fuel for our old used cars. Av gas is highly controlled because lives are on the line.

100LL avgas is not really low lead content, it’s just lower then the 130/150 it replaced 30 years ago. 100LL has a pump octane of about 110. Running pure avgas will turn your exhaust chalk white and leave deposits on you valves. I had a near unlimited supply of free 100LL. Once removed from a plane for maintenance it cannot be put back in the planes fuel tanks, or put back into the fuel truck. It’s considered contaminated. So, at work there was always a 55 gallon drum that needed to be emptied. I ran hundreds of gallons through my vette. Oh, that smell. It’s like a pheromone for car guys.

When I tore my engine down in 2006, the valves had lead deposits. I now run 50/50 at most, but a 25% mix will allow the most aggressive of timing maps with no detonation issues.

Im surprised the FBO will sell it for known auto use (no road tax so it’s against the law to pump into a car) and most will not pump it into a can.

I didn't ask about pumping into the vette. I only inquired about price and if I needed a special fuel can to make the purchase. Very small AP in as very small hometown.

I have a buddy who is a private pilot. I've bought 100LL at one of the local airports on several occasions when I've gone flying with him.

You cannot drive a car onto the tarmac and fill up. You have to pump the fuel into a 5 gallon (or more) container. That's what I've done.

There is also a local gas station that sells 110 octane CAM 2, or Sunoco Race Fuel. It's $8.80 a gallon. Again, you can pump into a container, but you cannot pump into your car because of the "off road use" issue and the fact that taxes haven't been paid on it.

The biggest problem with 100LL is the blue dye that is included with the fuel. It is pretty aggressive and will eventually stain everything with a bluish hue. Its not super noticeable but if you look at your carb and tank after a few months you will be able to see a difference. The fuel has a heavier dye so that wing leaks and other fuel leaks around an airplane will be visible as 100LL evaporates pretty quick. In terms of what it will do to the engine there will be no major change on the short term but on the long term the lead will have a little more tendency to lead foul the plugs and ultimately leave some lead deposits on the valve guides. In fact, on aircraft we have a common problem of lead fouling so much that every year at annual you are required to pull and check all of the plugs. Just google aircraft spark plug cleaners and you will have a pretty good idea of one of the byproducts of 100LL use.

100LL avgas is rated using the "aviation method", which yields similar numbers to the Motor Method, which is usually 8-10 points above the Research Method, and the arithmetic average of MON and RON is PON, so the PON is in the 104-105 range that will support CRs up to over 12:1. Another advantage is that it is formulated with a higher distillation curve, especially the low end, to prevent vapor lock at high altitude. That's the source of the "formulated for high altitude" statement mentioned in a previous post.

In cold weather this could make cold starting a bit more difficult, but most guys don't report problems since these cars are typically only used in warm to hot weather. So even if you don't need the higher octane, the lower vapor pressure will usually prevent excess percolation and vapor lock that can be a problem on vintage carbureted cars.

I think the "lead content" is 0.5 grams per gallon, which is low compared to past avgas and mogas. "Lead content" can be confusing because sometimes it is specified as grams of lead per gallon and sometimes as cc of TEL per gallon, There is a way to convert one to another, but off hand, I don't remember the formula.

I suspect that for the price what the OP bought was "used" fuel that was removed from an airplane for maintenance purposes, but I see no reason not to use it as long as the FBO drained it into a clean container.

If an engine detonates on the best pump premium a 25 to 50 percent blend of avgas and the highest octane pump gas will usually quell the detonation unless the CR is way too high. You can get a ballpark estimate of the PON with linear proportioning. For example with a 25 percent blend of avgas with California's 91 PON the approximate PON of the blend is:

.25(104.5) + .75(91) = 94.375... call it 94 PON, which is 98-99 RON, and the slightly lower vapor pressure of the blend will reduce percolation.

More information on the various octane measurement methods and approximate conversion formulas are in my tuning seminar pdf that is attached to a thread started by me.

Duke

When I was an auto mechanic, back in the days of leaded gas (which had about 15 times less lead than 100LL), it was pretty common to do a valve job on an engine after 75k miles. All that stopped after no-lead became the law. When I first got my experimental airplane and ran avgas I was pulling a cylinder off every other year for an exhaust valve job. I switched over to using premium mogas in it 20 years ago and haven't had to touch the valves since. And yes, it is more subject to vapor lock and required the installation of a fuel pump cooler.

Avgas would run fine, but be careful, the airport is actually breaking the law, as there are no road taxes added in to the cost of avgas they sell. I doubt if you would be in trouble unless someone was watching them. Knew some guys who did this years ago, until the airport got caught and fined big time. Farmers don't pay road taxes either and aren't supposed to use the cheaper taxed gas they burn except in tractors and equipment.

The current lead limit for avgas is 0.5 grams per gallon Pb, which is considerably less than leaded mogas and avgas before lead limitations were implemented by law.

GM found that unleaded gasoline could cause valve seat recession in engines, primarily trucks that run at higher average load than passenger cars. That's why they started induction hardening exhaust valve seats on cast iron heads in the mid-seventies and is the source of the claim that when rebuilt, heads should receive hardened valve seats, but since Corvettes can only operate at full load for a few seconds at a time, it is unnecessary, and the risks of "hitting water" or seat dislodging is greater than seat recession. All aluminum heads, auto and aircraft, have hard seat inserts.

The mechanism is not well understood, but the belief is that a thin film of lead oxide is deposited on the seats, and that protects them from excessive recession. The film builds up to a steady state rapidly and is long lived, so if one is still concerned about seat recession, run some leaded gas through the system every few thousand miles.

Duke

Lucky you, avgas at $3 a gallon. Over the years I figure I've bought over 50,000 gallons of this stuff, OK most of it for aviation use. Here in Seattle the stuff is over $5 a gallon! I have an L79 car with 11.0:1 compression and I've been running 91 octane gas without ethanol. Seems to work OK. In another car I own it has a 283/283 with over 10:1 compression and probably will run OK on the same 91 octane as does the L79 car however I'm afraid of contamination from pump gas so I use 100 LL avgas. One of the main difference between car unleaded pump gas and avgas is the smell. The aroma of avgas is wonderful - to me and anyone who is around the car. Yes I deal with lead deposits... Al

Use this and save a trip/$

Wear gloves and dont breathe it!! I can run an additional 2 deg which is where it likes to be if I wanna play hard
Torco makes some nice products in cans that size also. jbsblownc5 is a distributor he can advise you on what product is best for you
http://www.wildbillscorvette.com/octanesupreme01.htm