I would find it hard to believe that the GAMI 100UL – the only contender AFAIK? – would contain that sort of garbage.
Car fuels, sure. There is a strong political drive to fill car fuels with all sorts of garbage, substituting 10% of the fuel with garbage and hoping nobody realises the car now does 9% less MPG 
Anybody who values their car is buying the most “premium grade” petrol or diesel they can get.
Silvaire wrote:
And I don’t expect 100UL any time soon, nor care very much either way. I don’t have a plug fouling problem and have no particular interest in extended oil change intervals.
Another problem related to 100LL is so-called “morning sickness” related to sticking or not entirely closing valves, caused by lead oxy-bromide deposits originating with the TEL in 100LL. 100UL should entirely eliminate that. Of course it can also be largely prevented in engines using 100LL by keeping the CHTs relatively high (350-400).
Highly engine and aircraft model specific though. The IO-550N in the SR22 is impossible to run much warmer than 300 degrees in cruise and the phenomenon still doesn‘t exist.
The problem with Ethanol in Mogas Auto-Fuels is not a problem for aircraft, boats have to deal with it as well, usually SP98 sold near marinas has less ethanol but with all salt & moisture around the quality is rather very low, many would have tested it: getting suck in middle of Atlantic vs getting stuck in Highway vs getting stuck in IMC at 6kft
https://boattest.com/article/beware-dangers-ethanol
https://boaterpal.com/what-fuel-should-you-use-for-your-boat/
chflyer wrote:
Another problem related to 100LL is so-called “morning sickness” related to sticking or not entirely closing valves, caused by lead oxy-bromide deposits originating with the TEL in 100LL. 100UL should entirely eliminate that. Of course it can also be largely prevented in engines using 100LL by keeping the CHTs relatively high (350-400).
I physically checked my Lycoming O-320 valve/guides via spring removal when it had about 1000 hrs TT, and they were completely free. I know the engine was run on unleaded fuel for a period before my ownership started at 800 hrs, although never since and maybe that played a role.
GAMI STC is out: 50$ per airframe and 500$ per engine, gets you a sticker to use G100UL
Ibra wrote:
50$ per airframe
I’d take the airframe sticker only, that is sufficient, don’t need to refuel directly to the engine. I’d pour the fuel into my airframe (i.e. fuel cell) and what happens thereafter is my own business 
Just for fun I went to the GAMI website and filled out the STC application for my single engined aircraft. I was amazed that the unusual type was there and that the N-number was linked to the FAA registry to load my address etc. But not thrilled to pay $320 (including $20 shipping!) to buy the STC for a product which is not available to buy. Apparently there is an applicable discount for “early adopters”, the ones who pay for the STC without actually being able to buy the fuel.
Selling rights direct to the consumer is wacky, especially when (if the fuel were actually available) you could buy it and burn it anyway, regardless of whether you’d purchased the STC, and leave no evidence that you’d done so. The way to get an ROI on this would have been to sell rights to producers. The fuel vendor couldn’t and won’t enforce the STC.
Also, given that my plane has a one-off field approval to use auto fuel, applicable to no other examples of the type, whatever stickers you’re buying wouldn’t be correct for my plane.
I’ll pass.
I’d take the airframe sticker only
You don’t need STC or sicker if you are not certifird, so maybe buy “EXPERIMENTAL” sticker
PS: those “EXPERIMENTAL” are way more expensive as it seems to be in auction by Carbon Cub Crafters (guys who fly 500k$ Cubs with 6 months product expectancy) as they look cool with that sticker
„Another problem related to 100LL is so-called “morning sickness” related to sticking or not entirely closing valves, caused by lead oxy-bromide deposits originating with the TEL in 100LL.”
It’s not just TEL.
It is soot and other combustion products in general.
If you lean your engine properly after startup for warmup and during cruise – you will not experience sticking valves.
