Good question! But don't you mean c as s or c as k?
Generally speaking, when e comes after (follows) the c the c is pronounced as s. That is especially true when a vowel precedes the c. Examples: race, space, nice, twice, since, wince.
The double c. When the doubled c is followed by an e or an i the first c is pronounced as a k and the second is pronounced as an s. Otherwise, the doubled c is pronounced as a k.
A c following an s is pronounced as a k if the following letter is an a, an o or a u. A c following an s is pronounced as an s if the following letter is an e, an i or a y.
Ch is a dipthong, and it is a combination of sounds. It's pretty much the same sound whether it is at the beginning, in the middle, or at the end of a word.
The C in 'special' is only pronounced /s/ if you're singing Bali Hai (from South Pacific) (and maybe also in Trust in me - from The Jungle Book - I forget). The first singers were foreign, and the second was a snake. ;-)
'Special' is two syllables - /'speʃəl/.
b
PS
Thanks for all the posts Ron - I'll try to piece them all together one of these days!