I think there are a slew of things that you can futz with on the 4 cylinder, since the KA24DE is the same motor from the 240sx and Altima. Look for intakes from companies that produce street products for those cars and viola, an intake for your 4 banger. Now, depending on how much money you're willing to toss around, I think you could turbo that thing and make it a beast. Anyway, just my two cents. Hope it helps.

ETA: Take the rack completely off if you want to reduce drag.