need more power on bottom end

[nismo300zx1990]

Do I have rebuild Mt naturally aspirated z and I have put bigger cams and ported polished heads, headers, new fuel injectors and fuel rail, unorthodox pullys, aluminum one piece drive shaft, and lots of other goodies but, my problem is that when my car was stock I felt like my car kicked in around 2.5k to 3k and now it kicks in at 4k. Is there a way to get hp at lower rpms?

[DCaff300ZX]

Nitrous?
The NA engine does not have much left in it as far as more power, and as a high compression motor can't be boosted much without detonation so what you have left is to move the power band around as you have with your mods. The stock setup is best for lower end power and normal-use type driveability, while any mods done move the power up the RPM range to better suit speedier acceleration or top speed.