This prodigious output comes by way of a 4.4-liter twin-turbo V8 and a two-mode hybrid system. The product of the now-defunct collaboration between GM, DaimlerChrysler and BMW, this hybrid system is fundamentally similar to that of the Chevy Silverado Hybrid and Tahoe Hybrid. Pairing these two power generators together is like dashing creatine powder onto a medium-rare strip steak.
This ActiveHybrid X6, then, is a hybrid with a chip on its shoulder, just begging to have its claims put to the test. And test it we did, strapping it down to a chassis dyno and making it sing. Er, whir and hum quietly.
Clearly, this is one well-endowed SUV, grinding out a near-flat torque curve from 2100 to 4800 rpm, and reaching a maximum of 402 lb-ft of torque at 4100 rpm. Peak power of 368 horsepower is reached at 5500 rpm.
These results fall far short of the manufacturer's claims. Now, there's always some drivetrain loss when you compare a manufacturer claims of a vehicle's output to a chassis dyno result of said vehicle, so the fact that our numbers don't match the claims is expected.
But how much drivetrain loss is normal? Ten percent? Fifteen? More? This has been debated endlessly, but the short answer is that there's no set number. It depends on many factors including the type of dyno, drivetrain type (e.g., automatic or manual transmission), tire inflation pressure, your cholesterol level, etc.
The GT-R is a 480-hp thing. So is a Porsche 997 Turbo. Both of those cars produce 405 hp (give or take a few hp) at the wheels on this very dyno.
The ActiveHybrid X6 is down 38 horsepower to those cars according to the dyno, so it could be that BMW is being slightly optimistic with the ActiveHybrid X6's 480-hp rating. Or it's possible that both of the other manufacturers are downplaying their cars' output.
What's more puzzling, though, is that the ActiveHybrid X6 is generating exactly the same peak torque at the wheels as the GT-R. You'd expect the BMW to be putting down roughly 140 lb-ft more than the Japanese supercar, but it just isn't so.