I think we agree on what the numbers mean, people doing things that may or may not be the best decision but all they have is thier own experience.Yep...that's how statistics work. A ~25% failure rate means that a quarter of the examples in a group will suffer a failure, not that a particular example has a 25% chance of failure.
Yes, a properly designed, properly constructed, properly operated, and properly maintained auto engine conversion can be reliable. The problem is, statistics show that the average homebuilder is unable to accomplish this. If you're a mechanic with 30 years' experience working on engines, you've got a VERY good chance of a successful conversion. If you're an average Joe barely capable of adding oil, and scrimping on every purchase to hold the costs down, your chances aren't so good.
I'd love to look at the changes needed to make to a Corvair to make them reliable...because, according my data, it hasn't happened yet.
About 40% of the accidents happening to Continental O-200-powered homebuilts are due to a loss of power for any reason (including pilot error). That percentage is 65% for Corvair-powered homebuilts. As far as accidents due to engine mechanical issues (including errors by builders or mechanics), there were six such accidents occurring to BOTH the O-200 and Corvair-powered homebuilts in the 22-year period covered by my data. But there were 120 O-200-powered homebuilt accidents in my database, and only 24 Corvair-powered ones.
According to the FAA registration database as of January of this year, there are about 700 O-200-powered homebuilts, and 56 homebuilts with Corvairs. Even if you assume the Corvair numbers are ten times higher than the FAA records show, that's STILL a higher rate of mechanical failure for Corvairs.
I'm not deliberately picking on Corvairs, since the data for most conversions is as bad or worse. I fully support people who want to use alternate engines...they just need to understand the risks are greater.
A new clean sheet design would recommend best practices. Car motors work great when the proper design is implemented.
You can use a simple screwdriver incorrectly and injure yourself or damage a part. Now take a complex design like a car motor FWF and now that same person who can't use a screwdriver properly is gonna figure is out?