My 470K is over TBO so I'll have to overhaul it one of these days.
But so far it's running great: good compressions, good oil pressure, and not making metal--
so I'll just continue to run it.
I've thought about ponking it when the time comes, or the equivalent from TS or whoever,
But I mostly fly light, and around the low country of puget sound where it doesn't usually get too warm,
and to be honest I'm satisfied with the performance as is.
I figure a ponk conversion is gonna cost me about $20K more than a stock overhaul:
$3K for the STC, and probably another grand of misc.
And about $6K more to buy new 520 cylinders,
vs overhauling the first-run K cylinders on my factory reman.
In between quality issues, and AD's,
I'm not too impressed with what I hear about new cylinders these days anyway.
Plus it'll be about another $10K to upgrade the prop from my current 88" C201 (not approved on a ponk).
Then there's operating costs:
I run mogas, which right now is running about $2 a gallon less than 100LL around here.
$2 a gallon x 12 gph x 100 hours = $2400 a year added operating costs,
or $36K over the 1500 hour TBO.
Another concern is that a friend of mine ponked his engine,
but afterwards had ongoing issues with severe carb icing.
He ended up installed Bendix fuel injection which cured the problem.
But it wasn't cheap-- I think just the field approval engineering data was close to a grand.
So bottom line, for me, the advantages of a ponk conversion are outweighed by the down sides.
