I have a 1990 b18a1 with an S1 transmission, I recently purchased a b16a with a good clutch, it is my understanding that I cannot use the clutch on the b16a with the S1 transmission in my 1990 GS integra, is this information accurate or am I able to use the clutch that came with the b16a?
Depends on what year the B16a was from. You could pull the disc and see if it fits on the input shaft of your S1.
the S1 uses the smaller input shaft like the Y1 & A1 transmissions. From 92 on they used a larger input shaft
I recommend buying a new clutch. I would never install a used clutch on any of my cars.