Lycoming doesn't approve of this because they haven't tested it, but others have and since it's experimental, you can test it yourself.
The FAA has said that 100LL will not go away until a suitable and approved replacement is in place. If your are still concerned that it will go away anyway (not that the government is ever wrong), you can run lower octane fuel in those engines using an electronic fuel injection/ignition system like SDS or EFII. Lycoming doesn't approve of this because they haven't tested it, but others have and since it's experimental, you can test it yourself.
Fascinating. So many rabbit holes to go down in this experimental world. If you run FI system, how do you handle various octane fuels? I know auto engines have knock sensors and can automatically adjust the spark advance to lower the power for lower octane fuel. Do these FI systems have a user controlled setting for that?
I imagine this has created some debate, so a "go search" is a fine answer.
I was reading about the possible end of 100LL. It looks to me like the 200HP IO 360 or the IO 390 are 100 octane only. Is this true? Anyone concerned about fuel type going forward?
There are also a lot of turbocharged certified aircraft engines out there that NEED high octane.. not to mention the tiny portion of warbirds that really need 130, I don’t think that we are going to lose high octane fuel.
George Braly's GAMI 100 fuel has been issued a blanket STC for all piston engines rated for 100LL - but no one seems to be willing to discuss it. Not enough paid lobbyists.