so it's 'vlky' because it is accusative?
you can go here and put singular nominative in the first window. Upon Enter you will get a table with all the cases...
Why is there no consonant shift?
There is one in Nom (vlk -> vlci), but not in Acc (vlk -> vlky).
I might be wrong, but I think it is because -y is a hard vowel, so you don't need to change the k, which is also hard. However, if you happen to add an -i, which is a soft vowel, you have to turn k into c, like in kluk -> kluci.