the issue is the stock Bottom end of the car was never meant for boost, so they get really finicky real quick
if money truely isnt an issue id be looking at tearing out the engine, and upgrading the pistons with a lower compression piston ( something like (9:1) and then upgrading the rods to something thatll hold power
after you do that, throw a turbo on the car, and then the next weakest link will be oiling. There's talk about upgrading the oil pump to something with higher pressure, but really we need something to lower cavitation
a better pickup would help, and dont forget an oil cooler
after you get that sorted youd probably need to swap out the injectors and fuel pump for more power. and there are 8 injectors on this car remember.
then the next weakest link becomes the differential. its just a small subaru 7 inch unit. never meant to take a whole bunch of power. the best idea would be a mustang IRS rear end from the newer 2016+ as its an 8.8 ring gear and can take beef'
unless you can make a Nisan R200 or R230 diff fit, those are common, after you get that sorted the next weakest link would be the transmission
I personally like the CDoo9 nissan 6 speed, but you can make a bmw ZF work, or maybe a tko500 if money isnt a problem
now just about the only thing that isnt modified is the interior.
you have to love the car an aweful lot to invest that sort of time and money, but if its up your creek. that's where Id start
MA Performance engine
Killer B Fury Turbo Kit
I personally recommend running nothing bigger than garrett sized GT3071RS, youll need the airflow to spool anything bigger.
and
Stage 2 Built heads
thats not including an aftermarket ECU, personally I wouldnt run anything less than a Link harness, though Motec would be ideal if money isnt an issue
Motec plug and play BRZ
Throw in things like an upgraded drive shaft, clutch, brakes and wheels and tires, maybe suspension if you get too wallowy with the power on stock suspension. and lets not forget a bigger radiator and intercooler upgrades. Dyno time, custom tuner..
just doing rough math, youd be about 20k into this car to dyno 350 whp
like i said you have to love this car powerful hard to put in that much effort and money