I just want to now for example if my b16 DOHC dc sports 4-2-1 will work on a friends 91 si I have a 90 si. He has a 4-1 and wants mine and i've been wanting a 4-1. Are the piping size the same?? i have'nt looked at his but he has mine and says it'll work and thier the same size piping. Will they even bolt up? What are the differences?