The last GTSIO powered aircraft I flew had over 1400 hrs a side with NO cylinder work. Temerature management is the key to the longevity of any turbocharged engine. Airspeed, mixture , and cowl flaps ( if fitted ) will all affect cylinder temps. The goal is to keep all the temps mid green from start up to to shut down. The problem is all the big flat sixes started life as 260 horsepower engines. They have been boosted up to 435 horses with the same cylinder sizes, resulting in a lot more heat and stresses on the cylinders, thus reducing their tolerance for the effects of less than optimal handling.
With respect to the C 421 Continental GTSIO 520 engine my SOP was as follows
1. Idle at 900 RPM, cruise at 1800 RPM which is supposed to be the most favorable harmonic for the gear train.
2. Allow the engines to fully warm up before exceeding taxi RPM
3. For mixture control,
a. aggressively lean on taxi to avoid plug fouling,
b. full rich for TO and climb
c . lean to 1440 TIT or 22.5 GPH on a digital ( shadin ) fuel
flow meter . This is about 3 GPH higher than book but is
only way to keep the cyl temps reasonable
d. leave the engines leaned on final approach unless a Go
Around is necessary
4. Plan your descents, gradually reducing power to about 24 in and then using drag to decend. Avoid as far as possible high airspeed low power situations. you should be able to fly the whole circuit or approach at 20 in , only reducing power in the flare.
5. Listen to the seat of your pants. If the engine is not humming smoothly it is probably too rich or too lean.
While this is specific to GTSIO engine, It is good that you create good habits in your students regardless of the engine type. The number one good habit I tried to impress on low time pilots was to avoid frequent power changes. to the point of limiting the more advanced students to three throttle movements from cruise to short final. This payed big dividends in forcing them to think ahead and fly accurately especially driving home the relationship between airspeed ,attitude, and aircraft configuration at any particular power setting. I felt this built good habits for when they moved to larger aircraft.