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.
Dyno charts and photos after the jump.
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 (check out our GT-R dyno test to see just how much they can vary). 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.
Jason Kavanagh, Engineering Editor
sgude says:
07:57 PM, 02/ 3/10
I think it is clear from acceleration test results I have seen published that Nissan and Porsche are underrating their vehicles, but I don't believe it is by that much. Is AWD launch really worth that much in a drag race?
However, that doesn't mean BMW is not publishing a higher figure than the X6 truly makes. Who knows what factors play into this? Heck, my 181 hp 325i feels stronger in the real world than its puny rating would indicate... guess you never know until you get it on the track.
thaitanium15 says:
10:13 PM, 02/ 3/10
I believe Nissan "overrates" their hp numbers.
israil says:
08:28 AM, 02/ 4/10
Those numbers seem more like what the 4.4 V8 should be making without the hybrid system. I imagine the hybrid system probably doesn't translate its added power well to a dyno run (or it just plain wasn't working). You should drag race a standard X6 versus the hybrid version to see how the results stack up.
cr_driver says:
09:42 AM, 02/ 4/10
I applaud Jason`s idea of this dyno test.
But as he states, "Dyno testing hybrids makes my head hurt", the right path is this one
"Guess we'll just have to wait and see if the ActiveHybrid X6 matches BMW's acceleration claims."
Already waiting.
orbit09 says:
11:28 AM, 02/ 4/10
The whole point of such a car is to be economical. In the tahoe, hybrid is just a selling point. Big SUV hybrids still get crappy milage on the hwy, there's almost no improvement. A 400+ HP TT V8 itsn't exactly game-changing unless it gets 30MPG hwy
lt1boy says:
01:47 PM, 02/ 4/10
368 hp and 402 lb-ft at the wheels translates to 433hp and 473 lb-ft at the crank, given a 15% drivetrain loss. That's a far cry from the 480hp and 575 lb-ft that BMW claims.
Having said that, that's one meaty torque curve there.
TPAWRX says:
07:43 PM, 02/ 7/10
I still think the X6s are ugly but even if you don't know what it is it sure makes a statement, it definitely looks like something special.