Since Reciprocating = Maintenance Your best choice in a prime mover APU engine on the used for cheap aftermarket is a : capstone c30 air bearing turbine engine with high efficiency waste heat recouperator.
Capstone Micro Turbine Natural Gas to Electric Generator Model 330-30 | eBay
Rated for 25,000 hours of nonstop continuous full power delivery of 30 kW or 40 HP, between inspections. The capstone could power your Nissan leaf at over 80 MPH continuously down the freeway for over 3,000,000 miles! And not one drop of messy lubricating oil or gross oil filters ever need be changed!
Though you will go through many tires, several CV axles, and a barrel of bug juice....
IMHO this type of prime mover is the only that should be allocated resources and materials to be produced globally.
Now with the transmission difficulties of efficiently coupling 100,000 RPM to the road solved by the advent of the electric power train, and both now available cheap on the aftermarket; it would be the choicest persuit of any serious ecomodder.
We need a topic in our forum full of case studies of ecomodder built turbine electric hybrids.
Wrightspeed Announces Super Clean Garbage Trucks | Wrightspeed Powertrains
If garbage trucks can see such vastly improved fuel economy, imaging what us ecomodder will do!
Even now Nissan leaf and even tesla power train parts are hitting the cheap used aftermarket on ebay for us to start building with.
2015 Nissan Leaf Complete Powertrain Motor, Transmission, Inverter and Charger | eBay
If interested I have a c30 turbine APU engine without grid tie circuitry and cabinet for such a build I could part with for $3500. Just PM me.