I have read with interest many of the posts on this subject. I too, had considered an automotive engine to the point I acquired the engine and designed most of the systems. I was convinced (and still am) that an automotive V8 run inverted, turbocharged with direct drive to the prop could do an effective job. But....
Brent makes many good points and I agree with them, but engines are inanimate objects and don't respond to the intent of the designers - they only respond to the details of the design itself. So what makes the liquid-cooled automotive engine inappropriate for an aircraft application? Liquid cooling helps, as a smaller bore with cooler surface temperatures allow a higher compression ratio, but the slower-running large displacement aircraft engine has lower friction, negating the benefit of the higher compression ratio. An efficient radiator can cool with less pressure drop, but it requires about twice the air flow of an air-cooled engine. The liquid-cooled engine can be more compact, reducing the frontal area, but the frontal area of a side-by-side seating aircraft is usually determined by
the cabin, not the engine. The list goes on.
Is the aircraft engine old-fashioned? The configuration has been around for a long, long time, but that doesn't have much to do with the effectiveness of the engine. The engineers at Lycoming and Continental have cherry-picked the technologies developed by
others that apply to aircraft engines, and developed some of their own. Bottom line? I'm happy with the 50-year-old Lycoming in my ES. And while I usually wish for a turbocharger when getting out of my 3800 ft, 7000 ft elevation runway, once in the air the fuel efficiency of the high-compression, naturally-aspirated engine is nice.
Gary Casey
ES #157, naturally aspirated Lyc IO-540