I did a search but because everything but "difference" was too common to search for it was not useful. I am still new to the FC and want to know the difference between an S4 and an S5? Is it years based or something else?

 

S4 is 86-88. S5 is 89-91. Lots of little differences, rubber trim strip, automatic seatbelts, 1000 rpm in N/As, compression ratio, more boost in turbos, etc. There is a list of the differences in the FAQ I think.

 

there was just a thread about this, maybe someone will post a link