Actually, some years of the Civic si do require premium. So do the new Focus SVT, Cooper S, GTI, '94-on Integra GS-R, S2000 (11:1 compression ratio from the factory!). My older stock Civic si doesn't require it, but nevertheless it is only a tenth slower to 60 than my A-code Mustang...i always laugh my butt off when my friends say hey i put premium in my car and i can feel the power difference....in a honda civic? ..sureeeee.