“with the real issue being whether anybody is going to do the tests and approve it”
I understand that there are some test results covering some traditional engines due in the next few weeks. I will post more info when I get it, but it could move us quite a long way. I think getting all traditional engines approved without modification to the engine is unlikely. The expectation appears to be around 80% - which at 20ppl less than 100LL (current price difference) will be a real plus for many.
Rod1