Why would you fly a C182 at 18"/ 2400 unless on approach? 2400 is max rpm. I use 22"/ 2000rpm for economy. Light weight it gives 120kts and 9.5usg per hour. (C182T normally aspirated).
That's what the POH says you need for 65% cruise at FL120 with ISA conditions. At FL120, 18" is the max MP. Of course you can fly lower, you can fly slower but I thought 65% and FL120 are sensible parameters to make my point about turbo normalizing and lower RPMs for a given power setting
