Hmm, I know wheels with 6kg in 18inch.... it's not unique
Well, right - haven't seen the "B" after the "B18". The B18C6 is the EDM (Euro-Spec) ITR Engine. It has little bit more power than the B18C1 that's available in the states. But you have to think about that we have much better gas than you. Standart right here is around 95octane, 100+octane is available as well.
That's the reason why J-Spec and E-Spec engines mostly has a bit more power than USDM motors, because both has 100octane and are able to set the ECU, resp. the ignition the an advanced level, and sometimes more compression.