Stock RB25 turbo:
Compressor
48mm inducer x 66mm major compressor wheel in a .60 A/R compressor
housing.
Turbine
51mm inducer 43mm exducer in a .5 A/R turbine housing
Stock RB20 turbo:
Compressor
42mm inducer x 59mm exducer in a .50 A/R compressor housing.
Turbine
51mm inducer x 43mm exducer in a .4 A/R turbine housing.
**rb25 turbo is slightly better, get a gt3071r and that will be MUCH better 