Update
Another way of looking at this by "first level approximation" is:
15psi = 2 atmospheres
8psi ~= 1.5 atmospheres
18 CR x 2 atmospheres = 36 CR
21.2 CR x 1.5 atmoshperes = 31.8 CR
So, I believe the calculator is accurate! I would never have thought that any engine would be able to handle a 32 much less a 36 CR. This is why it is necessary to reduce the typical 6.5L CR from 21.2 to ~18 to run 15psi of boost.
93 K1500 Ext. Cab, 6.2L D, 4L60-E, 3.73, 174K, 3" exhaust, air cleaner mod, EGR mod, EPR mod (my toy)
04 Dodge Dakota Sport 4x4, 4.7L (gaser), 545rfe, 3.92, 95K (wife's ride now)
98 K1500 Z71, 6.5L TD, 4L80-E, 3.73, 170K, 2.25" Crossover, 3.0" Down Pipe and Exhaust (sold to brother)