S4, S5 explanation please.
 

I'm new to this group although I just bought my 4th RX-7 (my 76th vehicle). What does S4 and S5 mean. I can't seem to find a definition anywhere. Searching on S4 and S5 brings up about a million hits but no explanation. Thanks!

s4 is the years between 86-88 rx7s (fc's) made
s5 is the years between 89-91 rx7s (fc's) made

I have a related question to that: are there any S's besides S4 and S5? Those two cover all the years for the FC, so would S1-S3 be the SA and the FD is S6+? Or am I totally making stuff up?

You are correct, sir. Although, I think S1 thru S3 are the FB's, the SA I am not sure even fell into the number series (but I could be wrong).
Oh, yeah, the 'S' stands for 'series', as in 'Series 4'.