Apart from their expensive but fuel efficient 99d tuning program for the Z4 roadster, the Germans at AC Schnitzer will also bring the ACS5 Sport S at the Geneva Motor Show in a few days, with this second upgrade aimed at the 2011 BMW 550i, and packing exclusivity and performance into the latest generation sedan.
The AC Schnitzer ACS5 Sport S BMW 550i comes with a 4.4-litre twin-turbo V8 modified to produce 540 HP and 750 Nm, which basically means a 133 HP and 150 Nm of torque increase over the stock version. In terms of performance the AC Schnitzer ACS5 Sport S BMW 550i will dismiss the 0 to 100 Km/h acceleration in 4.5 seconds plus it will be capable of reaching a top speed of 320 Km/h.
That all sounds very good, but what do all these figures mean when it comes to fuel consumption? well according to the German tuner, the AC Schnitzer ACS5 Sport S BMW 550i maintains the same level of efficiency as the standard 550i. 

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Source: AC Schnitzer