In Vowel-Consonant Patterns: Part 1 (WW2002249) we found that there are 256 (2^8) 8-letter vowel-consonant patterns - 128 beginning with a consonant (C Patterns) and 128 with a vowel (V patterns). When it comes to heterograms (all letters different), these numbers are reduced. This is because there are only 5 different vowels available (a, e, i, o and u), so that any V-C number of C patterns available in reduced by 8 from 128 to 120; the number of V patterns is reduced by 29 from 128 to 99.
"Vowel-Consonant Patterns in 8-Letter Heterograms,"
Word Ways: Vol. 39
, Article 6.
Available at: http://digitalcommons.butler.edu/wordways/vol39/iss3/6