"It's not the idea. It's the execution."   Ted Noel   I could not agree more.  All the theoretical  arguments seduced me (and others) into wasting time and money on a V-8 adaptation to the Lancair IV.   Product designers (I used to be one) learn time and again that customers are highly inventive when it comes to developing ways to cause failures.  If it were not for the real world experiences, reliability would be much higher.  <sad.gif>   However, I have learned (and probably always knew, if I were not such a blind aviation optimist) that reliability comes from hundreds of units operating each for thousands of hours racking up millions of cumulative hours of fleet experience, all under the watchful eye of a closed cycle monitoring and corrective action system that quickly detects faults and immediately addresses them.    One project can not test an engine enough to guarantee reliability.  A company with very deep pockets and a good reputation can test the hell out of the engine to assure a reasonable chance of success, good enough that  some launch customer will sign up for initial production.  But customers find situations that the engine manufacturer did not dream of or test.   Consequently, only with large fleet experience and a an excellent feedback system can you get the kind of high reliability we now take for granted.   Could someone take some liquid cooled V-8 (or 12 or 6) and make it reliable?  Yes, if they can get hundreds of customers to shell out money and continue the "test program" years after the initial phase is completed on the test stand and some early aircraft flights.    There is no compelling reason to do this in general aviation with piston engines.  It is one reason why piston engines have stagnated, and turbine engines keep creeping  forward, getting better and better.  Millions of hours of operation, all closely watched.  That is the key.   Sadly, I believe there is no other way.    Fred Moreno