I have a 95 240sx and i was told by a reliable source that it might be possible to change the intake cams out with another set of exhaust cams to create more HP. If anyone has any information on weather this will help my KA24DE let me know.
I'm not totally sure. But I'm pretty sure you have intake and exhaust "valves", and a "cam(s)" to activate them in time.
You can definitly get more horses by installing a more aggresive cam(s).
As far as valves,springs and lifters, I'm sure you could get some top end work done that might give you some improvement.