most JDM cars have a 180km/h speed cut built in
this includes R32,R33,R34
its usually a voltage signal to the standard ECU, the voltage increases as your speed goes up and reaches a certain voltage at 180km/h
most speed cut devices simply cap the signal so it never goes above say 0 or a very low speed so the ECU never see's voltage around 180km/h
there are a few ways to avoid this "cap" these are all coevered by searching, the speed cut has been done to death but as you haven't bothered to search;
1). cut the speed signal wire to the ECU (breaks HICAS diagnostics if you ever try it)
2). get a speed cut device (hks speed cut defencer, Apexi RSM, greedy make one too)
3). remap the ecu and edit the speed cut value
4). get a stand alone ecu