Dynamometers are notoriously tricky beasts, and comparing between systems, individual examples and even on the same machine across time can be hard or impossible. But they do serve to give a rough ballpark figure, and one of the latest tests of a 2009 BMW 750i reveals it's in a very interesting ballpark.

The numbers put up by the car - an Edmunds long-term test vehicle - revealed wheel horsepower and torque figures very close to the claimed bench numbers. Running the 4.4L twin-turbo V8 on a Dynojet chassis dyno, they found it rated at 391hp (292kW) and 434lb-ft (588Nm) of torque. The peak RPM figures also differed slightly from BMW's claimed maximums, with horsepower arriving about 300rpm early at 5,200rpm and torque coming on 1,500rpm late at about 3,300rpm.

Still the torque curve is satisfyingly flat from roughly 2,500rpm to 4,600rpm, providing lots of punch in the mid-range, where it will be most easily appreciated on the street.

But no one's doubting the car's performance - in fact, quite the opposite. Posting numbers that reflect crank power of closer to 450hp (335kW) and 510lb-ft (691Nm) of torque, the 750i is, despite its huge size and imposing looks, a classic sleeper - quick enough to rate 5.2 seconds in the 60mph dash and 13.5 seconds at 103.7mph in Edmunds' testing.

The turbocharging surely helps to produce this flat power curve and impressive speed, but with such conservative ratings from the factory, you have to wonder how the 536hp-rated V12-powered 760i would fare if strapped to a rolling road.