You can use rb20 pump but u need to remove the inside "guts" for the hicas or power steering fluid will leak everywere (which i learnt the hard way) lol and its less work to use the std pump and rack, altho the pump will bolt onto the rb20 but doesnt sit straight, I found the easiest way is to get the pump bracket off a rb20de which is a non hicas pump wich is identical to the s13 ca pump