My old 97' Civic CX Hatch got 35-37mpg on the Hwy and 33-35 when it was half city/hwy driving. That was when it was NA with I/H/E. After a Greddy 15g kit, JRC FMIC, P28, and misc. mods it was getting the same if not slightly better gas millage. It's all in the tuning under light load, and in the RPMs where you spend most of your time driving.