DirtyProp: Don't forget the Rotax 912.
Certainly not comparable with the average O-320, but I think they proved a point.
My opinion is that nobody knocked Lycos and Contis off mostly due to the certification costs and the very small market which precludes any return on the investment, not really because they are efficient.
I hadn't forgotten about the Rotax 912. You might note in an earlier post I said "
Successful geared aeromotive engines of more than 100 HP with less than 9 cylinders are pretty thin on the ground". While some versions of the 912 may produce slightly more than 100 HP it was the 912 I was thinking of when I was basically saying there were successful geared engines of less than 100 HP.
As you point out the 912 isn't comparable with the average O-320. No one has successfully replaced the likes of the O-320 or larger sized engines. Plenty have failed trying.
You seem to infer the Lycomings and Continentals are inefficient. Do you have facts to back that up?
If they were as inefficient as some on here suggest, the cost savings would be such there would be viable replacement engines on the market.
The real driver for diesel engines isn't efficiency, it is Avgas non availability in some parts of the world.
As and aside, it's interesting Cessna have dropped the C182 diesel engine option. They had diesel engined aircraft ready for sale once they had the diesel engine certified. They have quietly gone and refitted Avgas engines to these airframes.