The gain is 32hp 24lbs tq, the only mod the car had was an ECU upgrade. The dyno result might seem high but our UK office see's gains of 42hp +, these numbers are normal for a good tuner.
If your stock M5 is reading less than 440-450hp, you might want to consider using a different dyno.
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If you pair this tune up with the European Launch Control then you'll have a serious beast on your hands.