hello great community. Right, im getting real annoyed with all these tiny turbos or several newer n/a's thinking they can test a skyline & when i let go the gap just aint right, literally 
mods i've got on my motor:
straright through rumbling free exhaust.
Fmic
hks filter.
manual boost controller.
stock turbo
uprated ecu think its apexi - i checked it & its a jap1
standard oil & fuel filter
not sure of fuel pump so guess stock.
thats bout it for the engine part. now boost comes on good
& boost controller starts butting in at 4.5k revs. this is another annoying bit i'll up the boost on this for sure. i remember having my ca18 it never had a boost limiter & really revved hard in higher revs but my rb struggles to get close to six.
anyway apart from the top what else would i need for improving bhp on my motor.
thanks to all ya geniuses.
into the exhaust for a slight flamer 
happy days for sure, sorted & fixed. and on that let me say i've got huge flames coming out the exhaust which;ll tear down a tree