As Ross points out, there are numerous Subaru conversions successfully flying.
The key to that success though is that the majority (probably all) of those were built by someone who already had some background with engines and some knowledge of what it would take to make it work (and the rest they researched and learned along the way)
The problem with that is that the majority of people that have installed a Subaru engine (in RV's anyway) did so on the premise that they were purchasing a fully engineered and tested engine installation kit, and that all they had to do was follow the installation instructions and they would have a FWF installation that was modern/state of the art tech., at a lower cost than a typical Lycoming installation (who wouldn't want that?).
Ross, I am sure you can agree that that has never been reality.
Yes, I agree with most of what you've said here but we have hundreds of thousands of flight hours on Subarus all over the world proving that the engines are generally sound, outside of some well known issues like HG problems on EJ25s. As I've said numerous times, it's the details in the entire package which makes it work or not. Believe it or not, there are several dozen Egg Subes which have several hundred hours each on them with few if any issues. Most of those owners are not gear heads. RAF built over 400 Gyros with EJ Subes, very few problems. Over 125,000 flight hours on that fleet alone as of 2005. No idea how many now. They are still in production in South Africa, still using Subaru EJ engines.
My estimate is that there is at least 2000 Subaru powered aircraft flying worldwide, making Subarus the second most popular auto engines used in Homebuilts behind VWs.
I've never said the Sube is better than a Lycoming, only that it can work just fine at a fraction of the cost if the conversion is done right. Some folks just don't want a Lycoming up front...
It's simply tiring to listen to people who know little or nothing about engines, lambast auto engines in aircraft when they know squat about the subject or of the many successes. We've been involved with hundreds of auto conversions over the last 23 years. They're not right for lay, mainstream people in most cases but they work just fine for many others and have been failures for many others, generally because they lack the skills to build and develop a reliable package, which is a huge task. Those failures were rarely the fault of the engine in my experience.
All engines have their warts, good and bad points. Subarus generally don't suffer from oil leaks, oil consumption, stuck valves, separated barrels, cam corrosion, loose wrist pin bushings etc. The EJ25 IS well known for HG problems and some cases of valve guides moving in the heads, neither of which are usually sudden or catastrophic. Pick your poison...