Here is the facts: 1992 EG Civic hatch, JDM B18C or B16A motor. Since the EG Civic is lightweight then I'm theorizing that you wouldn't need a 421 header becuase the B18C and B16A motor is strong enough to pull it. So I'm sayin that you can use a 4-1 header and still have a quick Civic on the streets and great power on top becuase of the 4-1 setup, and if your lookin for more torque below then all you have to do is find a 4-1 anti-reversion or stepped header(a specially designed header that increases lower end torque by canceling back tracking sound freqencies that hurt lower end power). This type of header will work well for B16A EG Civic's. Anyhow this is my theoru so if anyone has anything else to add then do so.