As many of your have concluded, auto conversions are a realistic substitute for our airplanes. Given the continuous and generally trouble free service in automotive applications, there is no reason to assume that an airplane application woud result in failure. As long as the user understands that the airplane application will operate the engine at a higher power level than the engine sees in a car, then all other factors should be pretty much equal.
The problem therefore is not so much the engine but more so the reduction drive we place between the engine and the prop. In our research we have of course found many potential suppliers of redrives however, when we analyzed them for their published performance, we determined most to be lacking. To compound the problem, we have also discovered that many of these drives were generally "eyeballed" with no real engineering behind them. We also found that those who developed these critical components had no real knowlege of drive design requirements, nor of the potential loads that a flight environment will impose on the drive's components.
For those interested, I've posted a couple of engine/reduction articles at our web site. If you go to www.oriontechnologies.net and go the the Papers and Articles page, there are a couple of articles that talk about several of the issues to consider in this arena.
One interesting aspect of this is the real attitude of many of us who are considering an engine option for our airplane. We udertook a survey of the industry back in the mid eighties, and a supplementary one on the mid nineties. What we found is that there is tremendous interest in alternative engines. Virtually all responses (over ninety percent) respoded with a strong interest in automotive applications, reduction drives and all associated technologies.
However, when asked what engine all these people were most likely to put in their own airplane project, virtually all said Lycoming and Continental.
Thus far, we have therefore concluded that if an engine/redrive package is to be successful in the market, it first must have a professional level of technical backing behind it, it must appear professionally developed, machined and built, and it must be flight-tested to the level that a certified engine would be. This does not mean that folks want these engines to be certified, it just means that a substantial amount of testing needs to be behind it before the customer base takes it seriously.
Also, the customer must get past the company glitz, in order to do a real evaluation as to the suitability of the package. There are several companies out there providing redrives or drive/engine packages that look slick and professional - they are very well machined, anodized in pretty colors, and supported with slick sales brochures. But unfortunately they have virtually no real engineering, nor history, behind them.
There are a few good ones out there but discerning between the good and the bad is difficult. In essence, what this does is force the customer into the position of being a test pilot, something I'm sure most of us don't want to be. And so, most still consider the overpriced tractor-level technology standard to be the only choice for our airplane.
I think most of us would like this to change, but it will require a responsible approach to the development, and of course, a few dollars to make it work.