The Official 356Talk Forum

Mike Horton wrote: ↑Sat Nov 27, 2021 7:53 pm
...oh, the av gas, does Not have road taxes added, thus, technically not legal...

Legalities aside, the most salient feature of AvGas, aside from its 100+ octane rating, is that it still contains lead. The FAA, in partnership with research and industry entities, is in the process of developing unleaded formulations, but AFAIK it's all still leaded. I'm under the impression leaded fuel could be deleterious to our rebuilt engines.
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Lead is a very bad contaminant especially to oil and more so to synthetic oil which cannot absorb it so it precipitates out and can lead to serious problems which is why it was removed from the aviation market. Mike Horton could comment on that.

David Jones wrote: ↑Sat Nov 27, 2021 9:10 pm Lead is a very bad contaminant especially to oil and more so to synthetic oil which cannot absorb it so it precipitates out and can lead to serious problems which is why it was removed from the aviation market. Mike Horton could comment on that.

I had been reading an FAA web page wherein it states lead is still present. Perhaps they're behind in page maintenance. It didn't suggest any unleaded avgas is available yet.
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The prevalent avgas fuels today, are for on the order of 5 decades, termed "low lead", and yes, there has been a push for a universal aviation fuel. Factors are the octane required for what are considered high compression ratio, 8.5-9:1, VS the lower power rated training engines, and the many previously "FAA Approved" build specifications, through history, the resolutions for which are the challenge, between the FAA, and the engine manufacturers.

... a sort of "bean counter, engineering, and federal approval authority issue,"... what could possibly be the problem... ?

I sent Harry Pellow the lead contents of the various av gas in use back when he was writing his books.
There is a vapor pressure differential, as well...

Oh, there are a few "auto gas" supplemental approvals, each very specific to each covered airframe, with each specific engine installed, primarily for lower powered, under 7.5:1, and to be used under detailed parameters.

DO NOT USE AVATION GAS IN YOUR CAR! Aircraft are flown in higher altitudes than you normally drive! Aircraft engines work in the lower RPM than automotive engines. The air craft engine is cold and will remain cool during its operation. Reed vapor pressure of the aircraft fuel allows for smoother burning of the fuel at lower RPM'S. This effect does not change at the higher RPM's in automotive fuels.
Automotive racing fuel is available with high obtain and lead. It is delivered in a 55 gallon drum that needs to be stored carefully!! It will go bad over a period of time. It is a pain in the butt to fill your car from a 55 gallon drum even if you have an electric fuel pump with a hose. Stay with what you can get at a gas station that sells a lot of fuel zim

Back in 1954, when Pomona's drag strip was on the parking lot of the LA County fairgrounds in Pomona and was operated by the LA County Sheriff's Dept,, we used to make what we called "moon gas". I had a '34 flat head Ford with a slightly milled head and dual carburetors that I would run there. I would drain the regular gas, put in a couple gallons of moon gas, run my races and then put the regular back in to drive home. As I recall, the recipe for moon gas was 5 gallons of 100 octane avgas, 2-1/2 quarts of Toluene, 0.6 quarts of kerosene and 0.1 quarts of transmission fluid or light turbine oil. I think the calculated octane that resulted was somewhere around 104 to 105. Other than burning spark plug electrodes rather quickly, I don't recall any adverse reaction. I know the tailpipe would have a white coating on the inside afterwards.

I hope that Craig Richter stumbles across this and chimes in. He was running his Porsche there at about the same time. Teeny-boppers would paint your number on the rear side windows with Bon-Ami. Fun times. Eventually, they started messing about with nitromethane but by then I was getting frequent flyer miles in the USAF.

How does the volatility of the 10% ethanol mix sold in California compare to gas that has no ethanol? It seems like my carburetor bowls go empty a lot quicker than I recall from years ago. Not sure ethanol is the only factor.

I also am curious whether the early Solex 40PII carburetor tops with the tall skinny breathers would help to reduce the amount of evaporation. Anyone notice a difference?

Dave, from my reading it appears a 10% ethanol-gasoline mixture has a vapor pressure that is increased approximately by 10% over non-ethanol gasoline. Ethanol, in pure form, has a lower vapor pressure than gasoline. When mixed an interaction between the two raises the vapor pressure to a higher p.s.i. than either alone, to about E40, at which point it drops again to below gasoline. I suspect the gasoline available decades ago had a lower vapor pressure than any non-ethanol gasoline that is available today.

Tom, very interesting information, thank you for sharing. I think the ethanol mixture mostly evaporates in one week from my carbs. i.e. it takes a lot of starter cranks to refill the carbs. Another thought I had relative to ethanol volatility is that the large diameter breather tube in the top of the Solex carbs is not helping the situation. I wonder if going back to the early small tube tops would help prevent evaporation in any noticeable way.

Speaking of gasoline additives, I bought my car in CA in 1997. At the time, CA still used methyl tertiary butyl ether (MTBE) as an oxygenate in their gasoline. As I drove home with a full tank, a leak where the filler neck was soldered to the top of the tank allowed the fumes to escape and they were wafted back into the cockpit. An hour or so into the trip, I had to pull off the road and come back down from the high I was getting from the gas. I was so dizzy I could hardly stand and it took nearly an hour before I could continue driving. I understand MTBE was removed from gasoline in about 2005 in favor of ethanol. So, it could be worse, I guess.

For those that run any sort of Weber down draft carbs (46 IDM, 46 IDA, 48 IDA), I am finding that if the car is not driven for a couple of weeks I need to clean out the idle jets as they start to gum up from the ethanol fuel. Symptoms are a decrease in idle speed and a sort of Pfft back through the carb intake. Pulling the idle jets and cleaning them solves the problem.

Bill Sargent wrote: ↑Fri Feb 17, 2023 4:16 pm For those that run any sort of Weber down draft carbs (46 IDM, 46 IDA, 48 IDA)

Most common for a 356 would be 40 IDF. Would your observation still apply?
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Brian,

I am not familiar with the idle jet arrangement in the 40 IDF so cannot say. The carbs I mentioned are used on 1600 and 2 L four cam motors.

However, if you experience a decrease in idle and the Pfft back spit sound out the carbs, I would suspect that the idle jets are plugging.

This topic has come alive again. Recently there has been a lot of discussions about the ethanol mixed gas. It eats a lot of rubber parts: thus ethanol safe rubber hoses should be used instead of the Coline or other flexible lines, Zeniths have rubber o-rings sealing the jet covers, they aren't lasting more than 1 to 2 years max., ethanol attracts water and also scrubs metal very clean, making for the opportunity for rust in gas tanks and fuel lines, and it evaporates about 20% faster. PCA just released an hour long video about Fuel additives, Oils and Oil Testing, very scary, mostly aimed at the newer cars, but still can be considered for 356s. Here's the link:
https://www.youtube.com/watch?v=Oc4TBJPs8zQ&t=21s
What has been discussed on Rennlist and other internet sites is:
Top Tier gas, should be used, premium is best for our cars, it has been mentioned V Power Shell is good. When the gas evaporates it can leave some deposits and any water, that can build up over time, clogging the carburetor jets, Top Tier gas has better/more additives.
Oil should have ample ZDDP levels, around 1000-1300, and be changed twice a year, some mention of high levels of Calcium but have not found and data on that.
Fuel additives that have been mentioned are: Chevron Techron, comes in regular and complete, both could be as used for two tanks before an oil change. Stabil 360 which is used on a regular basis, and Stabile 360 Marine which is a stronger version, Techron Marine also cis to be used regularly year around, along with Lucas Safeguard Ethanol.
All seem to be pretty much the same, here's Techron's list: Distillates, hydrotreated light at 40-70% weight, Stoddard solvent at 15-40% weight, Solvent naphtha (petroleum), light aromatic at 5-10% weight, 1,2,4-trimethylbenzene at 1-5% weight. Polyetheramine (PEA) (detergent), polyether amines at 20-49% weight. PEA is the stuff that cleans and is very strong stuff.
The video that is done by Charles Navarro, who also want to market his companies products, but great information, it's makes you think about what could be happening.
For my 356, I use good gas, Shell Nitro V Power seems to run very good, also Costco, rumored to be Shell too in our area, oil is Valvoline VR-1 20-50 changed twice a year, I also have been using a little bit of SeaFoam now and then, for years, to dry up the fuel system, but then I do drive it year around and in a mild climate. The newer Porsches get Mobil 1 15-50, Premium gas, and occasionally add some Techron, oil changed once a year, again they are driven year around, but only about 2500 miles year.