Building on the statement “we need a new engine to solve the unleaded fuel problem”, I’m drawn to alternative engines that burn unleaded fuel. The Yamaha 4 banger liter motorcycle engine come to mind. These engines are ubiquitous, have a very tough service life but are known for reliability. Normal power output of these engines is 140 HP. Change the jetting of the carbs or flash the ECU and these engines easily make 150 HP. Add a turbo and 315 HP is achievable. Google Turbo F1 to see an example. There are probably hundreds of mechanical and reliability reasons why motorcycle engines would not be suitable in aircraft but it is a start. Interesting that the greatest contribution being made by the Samson Sky flying car could be the engine. They have been testing various engines to find the most effective and reliable solution. So far, the Yamaha engine is winning.