Originally Posted by DIGItonium

Maybe try to shed weight from the car? Every little bit helps... but it might cost you a bit (e.g., light weight seats, wheels, etc.).

When you go in for the tune, have them adjust the fan settings so it kicks in earlier and adjust the throttle map so the ECU will allow you to open it up more especially down low. Reference the tuning subforum.

[EDIT] IIRC, your might not be as daily drivable with this suggestion: shed weight down to 2800 lbs. Forged stripped down their stock Z to the bare essentials, and they managed to get it under 2800 lbs. or so and the car was highly competitive against the likes of Porsche on the track. Other than that... force induction is the way to go if you're going to spend more than $3k for N/A power.