Hi
This could be a Garrett GT3076 from Sonic Performance.
They sell 2 types of GT3076 turbochargers.
The normal (most popular) GT3076 has a 0.60 Surge slot Compresser housing.
Has a 57mm Inducer with 76mm Exducer compressor wheel
54.98mm exducer turbine wheel
The other option GT3076 has a 0.70 Standard Compressor housing.
Has a 55mm inducer and 76mm exducer Compressor wheel.
53.60 Exducer turbioe wheel
Can happen with many manual boost controllers.
I had a Manual Boost controller on my R34 which did the same, not as bad because of lower boost.
I Now got a HDI electronic boost controller which hits 12PSI and sits there
Yeah i run 12 psi. Which is safe.
My R34GTT Sedan Auto
Made 198.75KW ATW Dyna Dynamics Shootout
mods- Basic
700x300 front mount
3.5'' xforce exhaust
Hdi electronic Boost Controller
Splitfire Coils (std ones kept failing)
fuel ecconomy is the same 450-480klm
Also Lookup 'Nistune' for Re-map