When I had my impreza type r back in 2005-2007 I spent best part of £10k on engine mods to get it over the 400bhp mark...
Dunno if things are still the same but I'm sure back then 1997-1998 impreza ecus weren't able to remap them, only way to get more out of them was with new management???

I remember when I first got my type r, was running a uprated 2 litre short block built by Teg sport, walbro pump, vf34, gems ecu... Etc
That then was running around 330bhp max...

That did bottom end within 2 months of me buying it!!!

£10k later
Ej22t short block, uprated pistons, rods, 2.5 litre crank... Making it a 2.35 litre.
Md321t turbo, uprated headers, down pipe, fmic, 800cc injectors, baffled sump, Adaptronics ecu, inlet spacers...
A few other parts here and there... And the bloody thing still started to slip a uprated clutch at 22psi!!!
Was built to do 500bhp...