I drive hard on my car with a jdm b16 swap, as for engine mods I hav minor bolt ons, dc sports exhaust, removed cat, aem short ram intake, aem adjustable cam gears, msd coil, ngk spark plugs, denso iridium plugs. when I drive in city and rev frem 4.5k to 7.5k I still get 28mpg, and now with easier driving I get over 30 in city, I have also seen 40mpg on the hwy. so yes a 10s daily driver is and has been done, and when done right you will loose some economy but not that much, especially when compared to some domestic gas guzzler that is lucky to see 28mpg on the hwy.