One thing that is clear from looking at the dyno sheet is that this is easily a 500HP+ motor, if the turbochargers were able to keep maximum boost til redline (or even close). The torque curve is falling away quickly at a constant slope at higher revs which indicates to me falling boost levels. They have carefully managed the torque (boost) curve to create a plateau of HP til ~7,500 rpm.
The problem is that the goal should be to have a flat torque curve, not a flat HP curve. Because of the way that HP is calculated, HP rises with rpm (even when the torque curve is flat) - here they have tailored the torque curve to lose boost gradually at high revs to make a falling torque curve at the correct rate to produce a flat HP curve - this will make the engine feel anemic (running out of breath) at high revs compared to the last V-8 M3.
This issue is either caused by using turbochargers that are too small for max HP (but giving less lag) or by purposeful electronic control of the wastegate, or a combination of both. i.e. a GTS model with 525 hp could be made by BMW very easily (just by increasing the size of the turbos if necessary and allowing full boost to over 7k).
If it is just software, a re-tune alone could add LOTS of peak power.
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73 Carrera RS 2.7 Carbon Fiber replica (1,890 lbs), 06 EVO9 with track mods. Former: 73 911S, Two 951S's, 996 C2, 993 C2, 98 Ferrari 550