The rear drivetrain is designed to deal wtih approximately 60% of the vehicle's power, on a continuous basis. The rest goes to the front drivetrain. So if you were RWD only, you would be beyond the design intent, and if you modify for more power, even further off. Expect to break things.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue