In addition to diesels, a project is now underway to fit highly modified turbocharged Chevrolet V8 aluminum engines with fuel injection and electronic variable timing to a Cessna 421C. More power, much less fuel (28gph vs 38) and quieter. Inital cost is expected to be $60,000 per engine including the STC fee. Not a bad deal. The 421C is a very good aircraft now, with the STC it would be superb.