A simple box wires into the car's ECU and overrides the speed limiter, letting the car go as fast as it can, restricted only by power, aerodynamic drag, gearing and the intestinal fortitude of the driver.
With a 5.0L V8 pulling at 416hp (311kW), the IS F is capable of surpassing the electronic limiter, though by how much isn't clear. At any rate, there are other modifications that owners can perform to their IS Fs that would thoroughly justify the removal of the limiter, including turbocharging, nitrous and other performance-adding enhancements.
One fine example of a turbocharged IS F is the SEMA car to be shown by Artisan Performance. Rated at 600hp (450kW), the turbocharged IS F has a rebuilt engine to withstand the abuse, including new pistons and connecting rods and an up-rated radiator. With that much power on tap, 170mph (273km/h) could be passed with relative ease, and 200mph (320km/h) could be within sight, though aerodynamic factors tend to increase dramatically at such speeds.
The HKS speed limiter lifter is available now (in Japan at least) for ¥157,500, or about $1,550.