The reviewers over at LivingLifeFast have spotlighted another interesting tuning project: an E92 BMW 33i coupe that more than doubled its output thanks to just one turbocharger.
The stock inline-six under the hood normally produces 306 PS (302 hp / 225 kW), but once tuned, it churns out whopping 660 PS (651 hp / 485 kW) while letting the mill rev up to 7,000 RPM. The power measurements were made at the wheel, and the tuner used a gasoline-ethanol fuel mix for the tests.
Other than that, the car appears to be completely stock, so there is no way to figure it out for the sleeper it is until you hear the engine fire up.