Why not go back to radial diesels?
From the link
Radial engine - Wikipedia, the free encyclopedia
Packard designed and built a 9-cylinder 980 cubic inch displacement diesel radial aircraft engine, the 225 horsepower (168 kW)
DR-980, in 1928. On 28 May 1931, a DR-980 powered
Bellanca CH-300, with 481 gallons of fuel, piloted by
Walter Edwin Lees and
Frederick Brossy set a record for staying aloft for 84 hours and 32 minutes without being refueled. This record stood for 55 years until broken by the
Rutan Voyager.
A new Piper or Cessna would look awesome with a radial up front
