It may also be the way the ECU is programmed in your friends Turbo GSR. The sensors may not know what to do with this larger flow of air going into the motor. At other time I know that some after market ECUs that go along with forced induction kits shut off the vtec completely.
Best way to find out if it is affecting it is to check what code the ecu is throwing for the CEL.
MY check engine light is constantly on in my Type R but thats because of my racing cat
VTEC is fine though