Put it this way, if you buy the R34 GTR V-Spec already with the aftermarket exhaust:
- Upgrade the turbo's to Garrett -7's
- Get a set of Adjustable Cam Gears (fine tune the timing) or if you mechanic knows what they are doing and can modify your stock cam gears to make them adjustable.
- Upgrade ECU to an APex'i Power FC
- Set boost to about 1 Bar (14.7 PSI)
- Dyno Tune
You will see about 300 rwkW's, a nice number for the street.
You won't have to change the intercooler / air intake / BOV / fueling system as GTR running gear is capable of handling the power.