I remember changing the fuel filter on my car. After i finished, my car got crappy gas mileage. Like you said, around 20mpg. I found that i did not plug the charcoal canister hose back up that plugs into the firewall. I think that's what it's called. Anyway, after i plugged it back up, i started getting around 35mpg again. To answer your question, i doubt aggressive driving will make your gas mileage that crappy. You've got a problem somewhere. I'm talking about my stock si motor. I have no idea what your b-16a is suppossed to get on fuel mileage.