A company I used to do some casual work for had a fleet of Chieftains and the company policy was 31'' 2300rpm for the cruise. This setting was maintained in the descent (500fpm)
until reaching the circuit height of the destination airfield.
Upon reaching the circuit height power was steadily reduced to 25'' and maintained to short final, with the rpm being increased to 2400 (climbing rpm) just before turning final.
Power was slowly eased off from 25'' from about 100' above the ground.
In all my association with this company (about three years) there was not one instance of cracked cylinders.
