I was wondering about the model's of RX-7's how there called "FB, FC, &FD" Was there ever a FA? I was trying to look for something like that couldn't find anything.
and why are the symbols different on different generations of Rx7's?

 

I've never heard of an FA. There was an SA. That came before the FB, both were 1st gens. I believe the 79 and 80 models were SA's and the 81 - 85's were FB's.

 

exactly correct.

79-80-SA
81-85-FB
86-91-FC
93-95(USDM)-FD