RV-4 Engine
Wow, I think you may have just opened up a can of worms. I think that if you search this site you will find a full spectrim of opinions for and against just about every engine (even the Lycomings).
After you have read and researched all of the pro's and con's on each available engine it will still (in my humble opinion) come down to how much of an experimental pilot you decide that you want to be.
I think that most would agree that the Lycoming is the path of the least resistence. That is, the plane is designed around such an engine and is well supported in that configuration. Others seem to be gaining some ground in that area as well, but still far behind the "standard" system.
Personally, I am very intrigued by some of the conversions out there but at this point I am not willing to fly them. I am perfectly happy to let someone else do the research and development as I have no desire to be a test pilot to that extent.
One of the locals here installed one of the Subaru engines. It is a beautiful instalation, but he has had to do a lot of research on his own to get it to run correctly. Then in less than 70 hours the reduction drive went out and he had to buy a new one. I believe the company bought back the bad one for change on the dollar to try to determine what happened. I haven't heard the result of that yet.
This isn't to pick on the Subaru's or any other combination of engines. However, it is just an example of the efforts needed when someone uses a system other than what the plane was designed around. I think that you may even find people that have had problems with Lycoming and clone engines. I suspect that they are fewer percentage wise than with the auto conversions.
This of course begs the question of "how much development and research did Lycoming and Contental do before coming up with what they have now? The nice part for us is that it is already done.
Keep up the great work on all of those other conversions. I read of them with great interest. Maybe someday someone will hit a home run. Maybe even it has already happened and I haven't heard. That is one of the great things about this country. People are free to continue to invent a better mouse trap (or airplane engine).