there is a rev limiter in 4th and 5th gear. you usually don't get that far because of the speed limiter.
there are connections you have unplug/cut to get rid of the limiters.
I can't remember which ones exactly, but some google searching, or maybe 240sxforums.com searching should yeild the required results.

I know you can run an automatic ecu. that'll get rid of the limiters...it'll change your power band a touch, but not much.