There is a lot of bad info out there on auto conversions. My Cessna 172 has an aluminum V8 on it and works way better than the dinosaur 0320 it replaced. Not only does it out perform it, but it cost less than $20 USD per hour to operate compared to $68/hr with original engine. However, not all engines make good aircraft engines, and even then, require engineering skills typically outside a pilots skill set. My C172 is quieter, consumes any automotive gas or AVGAS you want to put in it- although I avoid AVGAS due to higher price and i need to change oil and clean plugs a lot more often due to the lead- and parts are cheaper....not to mention it doesn’t pollute the air as much. It even has OBD which displays fault codes if something goes bad, making maintenance easier....when was the last time you saw a modern car broken down on the side of the road? It’s also easier to fly with no mixture control or carb heat. Even the certified diesel aircraft engines use an automobile engine block.
the right converted engine is way better than the 1940 stuff the industry still forces down our throat, and in my opinion, more reliable. I currently fly the B787 and everything is electric, and very reliable. The only thing holding technology back is Lycoming and Continental that have not needed to improve their product because they have a monopoly so why spend the money. Certification agencies share much of the blame as well by using 60 year old cert regulations and demanded expensive cert process..