>>1861156Because those are low-compression engines and the power to weight ratio is not so important in those applications. A fighter engine is not the same as a bus engine. Even the Ju 87 engine was a second-tier engine, and when they used it in exported Me 109 airframes the performance penalty was unacceptable. So yes, if you need to burn a lot of fuel cheaply and you don't care about performance then it's fine.
The best piston engines nowadays are designed for sports where the rules dictate the induction system, so I don't know why it matters. And Diamond bought some auto conversion company, but that engine was and still is verifiably a piece of shit. If they can barely afford to develop existing auto engines, the development of some new layout is definitely impractical.