Tesla owner Emmanuel Chang had his 2013 Black Tesla Model S P85 dyno tested on a mobile Dynojet recently at some generic car show.
The Model S P85 is officially rated 416 HP (305 Kw) at the motor shaft. This particular combination of dyno and P85 recorded 436 HP (320 Kw) at the wheels. (there is usually a significant drivetrain loss between motor output shaft and wheels)
A few details regarding this test: