Hi and welcome to the TC forums.
As LM says changing the breathing, intake and exhaust, could release a few horses and make throttle response quicker. Don't know if changing the ignition will work on that engine but on my RB26 changing the coil packs, sparks and HT leads gave more power at top end. Both fairly inobtrusive mods, just remember to have all changes fitted first then custom remap on a dyno at the end to get best out of them