2010 BMW ActiveHybrid X6: Dyno Tested

At first blush, the idea of running a hybrid on a chassis dyno is silly. A dyno is all about power and performance, and a hybrid, well, isn't.

That is, unless the hybrid is the 2010 BMW ActiveHybrid X6, of which its creators reckon is the most powerful in the world. Have a look at its stats as claimed by BMW -- 480 horsepower and a staggering 575 lb-ft of torque.

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.

We used GMG Motorsports' all wheel-drive Mustang chassis dyno for this test. Mustang dynos typically produce lower numbers than an Dynojet or Dynapack dyno. So there's that.

Still, putting aside all questions about drivetrain loss, the bottom line is that this 480-hp thing should produce very close to the same power at the wheels as another 480-hp thing on the same dyno.

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.

The big wildcard in all of this is the X6's hybrid transmission. We performed our testing of the ActiveHybrid X6 with the transmission in the manual gate on the assumption that it provides a fixed gear ratio in the continuously-variable transmission. If the actual gear ratio was in fact changing during each dyno pull, then our results could be skewed.

Dyno testing hybrids makes my head hurt. Guess we'll just have to wait and see if the ActiveHybrid X6 matches BMW's acceleration claims.

We'll be posting a full test on the ActiveHybrid X6 in the coming days, and then we'll know for certain whether this hybrid lives up to its boasts of record-setting power.