Is there a difference in alternator pulley?
 

I'm just wondering if there's a difference between s4 and s5 alternator pulley. Not the alternator, but the pulley itself. I can't see to find out what the difference is.

Probably, none.

Guessing the shafts are a different diameter. Guess for right now. Pulley might have to be bored out more to fit the series five. Memory/guessing.

i know the fc/fd shaft is different, pretty sure the s4/s5 are the same...not positive though.

Hmmm... If someone has both alternator and wants to be a doll, can someone put up measurements?

s4 and s5 are interchangeable, just one is bigger than the other.

When you mean bigger, you mean in diameter? Is the shaft itself is the same? Finding s4 duel alternator pulley is easier than s5, if there is a difference.