The Tesla Model S is an undeniably quick car, especially considering its considerable weight. But just how much power does the world's only real electric car produce?

A lot, it turns out.

The team at Autocar took the Model S to the dyno to find out exactly how much power reaches the rear wheels. With a Tesla [NSDQ:TSLA] Model S Performance edition (with the + suspension package) strapped down and the roller spun up, the results are staggering: 428.2 horsepower at the wheels.

That's considerably stronger than a previous dyno pull with another Model S Performance performed earlier this year by Dragtimes, but whether that indicates improvements to the Model S itself or a rather massive variance between these two dynos is unclear. If it's a dyno discrepancy, it's massive; there's about a 15 percent difference between the two results.

For those paying attention, that 428 horsepower rating is 12 horsepower more than the Model S is rated at the electric motor's output shaft. Of course, an electric car has little of the drivetrain losses between the crank and the wheels found in a typical combustion-engine car thanks to its one-speed transmission. Still, that's a very strong result, indicating the Model S is quite safely underrated from the factory. On the other hand, the dyno could be correcting for presumed losses--losses that don't apply to the Model S.

It's also worth noting that while individual dynos vary in their judgment of a car's output, an electric car like the Model S has fewer confounding factors to correct for; ambient temperature, airflow, and other considerations for combustion cars simply don't apply.

Whatever your take on the Model S as a substitute for a conventional car, you have to recognize its achievements as a performance vehicle. Just not necessarily as a luxury car.