Hartge F21 M135i xDrive Engine Upgrade [Video]
The upgrade kit takes the M135i's engine from an already impressing 320 HP (420 Nm) to 367 HP and 520 Nm of torque. The 6-cylinder, 3-liter turbocharged engine will not be harmed by this transformation and Hartge even offers a 3-year-product warranty in order to keep your mind at rest.
Furthermore they even took the time to put together this video to show the potential customers just how the engine performance changes, instead of just describing it with fancy charts and numbers.
The final outcome shows a 3 seconds improvement in the acceleration time from 80 km/h to 200 km/h. That translates into a 44 meter difference between a stock car and a Hartge upgraded one at the finish line.