Insomnia strikes again. I'm going to convert the dice pools of Mansions of Madness into percentiles so you can convert Call of Cthulhu scenarios into Mansions of Madness scenarios.

Use the following to convert difficulty ratings to dice successes on the Mansions of Madness D8s which have a 2/8 chance of 1 success (not using clues)

25% 1 Die
44% 2 Dice
58% 3
68% 4
76% 5
82% 6
87% 7
90% 8
92% 9
94% 10
96% 11
97% 12
98% 13
99% 15
100% 19

Note that this is only the probability of 1 success.