It is not so much detuning the car, more changing the mapping to suit the characteristics of the turbo with restrictor fitted.
I was speaking to one of Toshi Arai's technicians and he said Toshi's car was making almost 50kg/m of torque, that almost 500nm if I'm not mistaken.
With a 32mm group N restrictor.

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F.B. Racing
01 WRX (STI badged)
2010 XR5 Focus
06 Impreza Hatch 2.0i