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I noted their numbers for the TSIO-550-N.
The
compression ratio is 8.5:1 and the oil capacity is 8
quarts.
Robert,
I don't know what a TSIO-550-N
is for sure but if memory
serves, Columbia flat rated their engine down to
310hp to get the longer TBO.
...so that may relate to their choice of
compression ratios, if it is not a misprint.
At any rate, there are more than a few TSIO-550's
flying now with the higher
compression ratio. The advantages of
that are: 1) lower CHT's due to the
fact that the greater expansion factor takes more
heat away and 2) 5% or
better improvement in fuel economy.
Personal belief is that you get to run at higher
power settings at high alt.
cruise because you aren't temp
limited.
If I had to do it over again I would certainly use
a 8.5:1 setup.
I think the 7.x:1 idea was that if you mismanage
your mixture you have
a little more margin at 7.x:1 than at a higher
compression ratio.
But the impact of mismanagement on internal
cylinder pressure is so
much higher than the impact of a slightly higher
compression ratio, I
don't see the sense in keeping the lower
compression ratio. If you would
blow up your engine at 8.5:1 you would probably
blow it up at 7.x:1 also.
Colyn
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