Real stats on engine failures?

"Kyler Laird" wrote in message
...
Don't forget that you're safest with a single-cylinder engine. If
you have a six-cylinder, you're *six* times as likely to have a
failure.

If the only thing that could go wrong with an engine was some sort of
failure of the cylinder, then that would actually be a pretty close
approximation of the truth. And in fact, if you have a six-cylinder engine,
you ARE (about) six times as likely to have a failure *of a cylinder* as you
would with a single-cylinder engine.

In the single vs. twin analysis, you have nearly double the chance of an
engine failure as with a single, all else being equal. If X (a number
between 0 and 1) is the chance of an engine failure for a single engine,
it's not that you have 2 * X chance of an engine failure for two engines.
You actually have 1 - ((1-X) * (1-X)) chance of an engine failure. But when
X is small (as it is in this case), the square of 1-X is pretty close to 1 -
(2 * X).

If all that could fail on an engine was a cylinder, or component related to
a cylinder, then a six-cylinder engine would be 1 - ((1-X) ^ 6) likely to
fail, where X is the chance of failure for a single-cylinder engine. But
just as 1 - ((1-X) ^ 2) is very close to 2 * X for small X, so too 1 -
((1-X) ^ 6) *is* actually very close to 6 * X for small X.

Now, with that essay out of the way, the real reason that six cylinder
engines aren't six times as likely to fail is that a number of failure modes
have nothing to do with the cylinder. They involve one or more other parts,
parts which exist in the same number regardless of the number of cylinders.

Note also that just as having two engines provides a benefit to offset the
very real increased opportunity for failure, having four, six, or more
cylinders provides a benefit to offset the very real increased opportunity
for *cylinder failure*. That is, with a six cylinder engine, if something
that IS specific to a cylinder fails, often the result is simply reduced
power, not a complete power failure.

...or at least that's what I've learned from some of the geniuses
who talk about twins vs. singles.

Sounds like you've got some good geniuses advising you. Stick with them.

Pete