German tuner Kubatech has developed a Stage II upgrade kit for the Porsche Carrera GT that raises performance by 48 HP and 52 Nm of torque.
The power increase results by adding a sports exhaust system from Cargraphic and a revised engine software, so instead of 612 HP and 590 Nm the Kubatech Porsche Carrera GT now unleashes 660 HP and 642 Nm of torque.
The tuner says 0 to 100 Km/h acceleration time has improved, while exact figures have not been specified, plus the Kubatech Porsche Carrera GT can now reach 343 Km/h instead of 330 Km/h.
Installing this Stage II performance kit on the Kubatech Porsche Carrera GT takes around 2 to 3 working days, with pricing for this conversion reaching 10,699 Euro. 
Kubatech press release :
Stage II – Porsche Carrera GT by Kubatech
Kubatech – an engine software expert from Mechernich – has increased
performance of the 612-hp Porsche Carrera GT by extra 48 hp. The top
speed increasing just by 13 km/h rises the torque by 52 Nm. Improvement
in performance is caused by modified engine electronics and the
Cargraphic sport exhaust system.
By this tuning, the Porsche Carrera GT has become more powerful. After
performance improvement by the software optimization, the power was
increased from standard 612 hp to 660 hp. At the same time, the torque
has risen from 590 Nm up to spectacular 642 Nm. The top speed of the
standard Carrera GT goes over 330 km /h. Engine tuning has reduced the
time of acceleration from 0 to 100 km/h. The top speed now is only 330
km/h instead of 343 km/h indicated in the data sheet.
A new high-grade steel Cargraphic sport exhaust system provides a fine balance of power and sound.
The cost of the tremendous increase in performance "Stage II" for the
Porsche Carrera GT is 10699 Euro including the exhaust system.
Installation takes about 2-3 working days, including special adjustment
using our proprietary dynamometer.
Photos by: Kubatech

Source: Kubatech