Higher compression engines do not need high octane...anymore. Look at GMs direct injection 3.6. They are making 300hp and more without using high octane fuel. 326hp and 87 octane. There are more examples. The point is that automotive technology has continued to evolve relatively, and airplane engine technology stopped..way back in the beginning of the century.

What you say used to be true, until automotive timing and control got good enough. Turbocharged engines will probably always need some higher octane, but there was a multitude of reasons that lycoming listed why you can't just go and put 91 octane in a lycoming and run it. The real dissapointing part IMO is that they have not been designing to overcome this the entire time, rather they want the fuel designed for their engine.

What I'm proposing mostly is that the engine manufacturers stop producing these archaic designs and put some money into designing something somewhat modern that you can use 87, 89 or 91 octane pump gas in. Not that you can go and put 94 octane in it and get "ok performance", but that the engine is designed to run on those lower octanes from the get-go. For all those "old engines" out there, I think modifications (ignition systems rather than lawnmower magnetos) and fuel system upgrades are realistic solutions. It just seems like "designing the fuel for the engine" is always going to be a losing battle, there won't be but a few refiners making it, it will be very expensive due to the scale of production, and so on. I realize that to some extent this might have to happen for a few of the warbirds so they can perform at shows, but otherwise I just don't see any realistic to 100LL.