Zenki's are 240sx's from 95-96, their front ends look a bit conservative, almost Camry-esque. Kouki's are from 97-98 and received a bit of a facelift with more aggresive slanted projector headlights and different tailights. Though apart from the bodystyle, all S14's are nearly identical in most other ways. I think Zenki means "early" and Kouki means "later" in Japanese.