what is the highest compresson rotors for a 2nd gen, and the s4 and s5 housings, are they the same size?

 

Highest compession rotor is the S5, and there is a difference between the S4 and S5 housings. I believe it is mainly just the spark plug holes on the S4 are a little close, or farther apart than the S5 (I can't rememer)

 

so the s5 NA rotors are highest, and would it make a difference if i had an s4 turbo housing with an s5 NA rotor

 

Yep, highest compression is in the 89-91 N/A. They are 9.7:1. Like said above the main difference in the S4-S5 housings are the location of the spark plug holes.