Intake NVCS (valiable valve timing control) is the reason. S14/S15 SR20DE has it and any FWD SR20 does not have it (except SR20VE's VVL system). NVCS is the old school valiable valve timing system and B14's GA16DE motor came with it. Another reason is the compression ratio. JDM S14/S15 came with higher compression (10.0:1) than US spec SR20 (9.5:1). Those two are the reason why S14/S15 Silvia SR20DE has 20 extra HP.
Oh, BTW, S15 SR20DE motor is 165HP.
See the bump where I pointed? This is where the NVCS sits. This is the S15 Silvia Autech version's 200HP SR20DE engine. I know.....