<<Combining the LL100 issue with hearing over this past 3 1/2 years the
reliability issues surrounding TSIO 550 on the IV P has me thinking it's
time to look for a better way to go.

Again, as a result of this web site, I was aware of the Engine Air engine.
Clearly, here again, major controversy exists.  Believe it or not, as I
investigate this engine further, it becomes harder to sort out the facts
about the reliability of this engine.>>

I don't have any factual information to help, but opinions might be all you
are likely to get.  Statistically, I'm sure there haven't been enough hours
on either engine to give a solid basis to make a decision.  FAA
certification procedures also don't give a basis for the determination of
reliability.  Reliability is an "attribute", meaning it either fails or not,
as opposed to durability, which can be measured in hours or thousandths of
an inch.  To have a 50% confidence in a MTBF you need approximately (not
exactly) that number of hours without failure - and that's to be only 50%
confident.  That means that your engine is just as likely to be less
reliable as it is to be more reliable.  What reliability are you looking
for - a failure per 100,000 hours?  Certainly not 1 per 1,000 and maybe not
1 per 10,000.  I doubt that there has been 100,000 failure-free hours put on
the 550 and certainly not on the Enginaire.  There is some data available
(actual failures) on the TSIO-550 that suggests that the 100,000 hour mark
is not realistic.  So you are left to judge by the design.  While the
Engineair looks like a very well-done design it is very complex compared to
the IO-550.

While you are worried about the end of 100LL you probably should be more
worried about how well each engine will run on 100LL, as it will be
available for quite some time in the future.  Here the 550 wins, in my
opinion just because the spark plugs are larger in diameter and therefore
probably will accept more lead before fouling.  By the time 100LL is gone
there will certainly be systems available like the PRISM that will address
the issue.  There may be a lot of valid reasons (I can think of only one) to
pick an auto engine conversion, but improving reliability is probably not
one of them.

Gary Casey
ES project destined for a V-8