Don't agonize.  Buy an aircraft engine.  A  proven package avoids future agony. 

 

The IO-550 and TSIO-550 operated 50F lean of peak will achieve fuel economy that is virtually indistinguishable from a higher compression liquid cooled piston engine.   And they will make the power with MUCH greater reliability.

 

I was involved in the Engineair project as were several others on this list.  Bad management, bad luck, and  inadequate financing killed it and several people along the way.  It may have made it under different circumstances, but it had a long way to go, but we did not know that).  It is not the engine so much as the systems that will kill you.  They are reliable only after thousands of hours of testing.

 

I am a mechanical engineer and an engine head, and I have learned that the engine business is very unforgiving and requires extreme attention to detail to achieve reliability which should be the FIRST consideration for an aircraft engine.  This is particularly true on an aircraft with a high wing loading and high approach speed. A lot of energy must be dissipated in a Lancair IV forced landing, and your body will be much the worse at the end of the energy dissipation process unless you are very lucky like I and my passengers were last year.  

 

Untested engines are for ultra lights that land at walking speeds.  With those things, one can have a reasonable expectation of walking way after an engine failure. 

 

I expect that of all the auto engine conversions flying, NONE consistently fly more than 50 hours a year, and NONE have gone more than 200-300 hours  (more likely 50-100 hours) without major difficulties, gearbox failures, fuel system failures, cooling system system failures, electrical system failures, ignition system  failures and other unhappiness.

 

Don't fiddle around.  Buy a proven aircraft engine from a well known, proven, and reliable supplier, and go flying.  Otherwise the agony will continue without end and the flying will be infrequent.  

 

Fred Moreno, been there, done that, and I even have the crummy T shirt.

 

PS since you are not-pressurized, let me put in a plug for the  IO-550 (no turbos).  Cruising 65% power, lean of peak, 13.5 gallons per hour at 220 knots 8500-9500 feet gives easy one day one stop trans-continental capability, light weight (1980 lbs empty weight) for a good rate of climb, and a much less boring ride than up in the flight levels here the world is flat and lacks detail.  The dirty little secret of aviation is that the bigger, faster, higher you go, the more boring it gets, sadly.  And remember: a turbo is an expense waiting to happen. Two turbos, well, you do the math....