13b... fc vs fd

whats the difference between the fc turbo 13b and the fd 13b? sorry if i dont know... but what makes the fd engine more powerful if theyre both 13b?

fd 13b is twin turbo.
fc 13b is single.

1993-1995 13B
- twin turbo
- more boost (10-8-10 pattern)
- lighter rotors
- stronger dowel pins to handle higher boost

1987-1991 13B
- older
- less boost (6-7 lbs)
- not as strong