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John:

You wrote that "It has a single electronic ignition", am I to understand
that there is only one plug firing in each cylinder? If true, this is bad.
The primary reason for having two ignition sources is to control detonation,
not redundancy. In a large diameter cylinder, the flame front can't
propagate fast enough to to burn all the mixture (charge) before heat and
radiation cause isolated pockets of charge to detonate. Having two sources
of ignition reduces the burn time, increasing detonation margins.

As you climb, the charge gets hotter as the the turbocharger compressors are
working at higher ratios and the intercoolers and cylinder fins have less
cooling air mass flow. You could be seeing the onset of detonation, which
would explain the rapid increase in temperatures.

Typically I climb at 85% power, 170-180 KIAS and 30-32 GPH producing a VSI
of 800-1000 FPM depending on load and temperature. At these settings EGTs
stay around 1350 and CHTs below 400 all the way up to FL280. Ignition timing
is set to 20 DBTDC static with both mags firing at the same time. There is
very little advantage to having the ignition timing advance on a
turbocharged engine as it is usually operating above 70% power.

Regards
Brent Regan

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