cagambler

Took a leisurely drive from Redding down I-5 at a few over the limit to avoid the usual CHP radar traps listening to my favorite CDs on the B&O stereo. Got 29 mpg. Can see Mt. Shasta from 130 miles away.

MCE Racing at Thunderhill, the SCCA-owned track in Northern California, has the only DynoJet Linx-424 All-Wheel-Drive dyno in Northern California. Kevin seems to know what he's doing and has interesting stories. He says Google rents the track once a month for any of its employees to come play on. Recently bled the brakes properly for a Google employee that bought a $1.3 million McClaren and tried to bleed the brakes himself and brought it to the track three days after he bought it. He did the dyno on it as we'll.

I've been reading that AWD has drivetrain losses of 20%. He measured (not estimated) the drivetrain losses at only 12%.

Oh, you want to know the numbers? Brake horsepower of 397.43 with losses of 53.31HP for crank HP of 451.
On crummy 91 octane California gas (although the track sells both 100 and 110 octane Sunoco) and test conditions of 98 degrees F. Torque of 402. Says the car is set really lean (California EPA again?) until 3500 rpm, making the value of launch control (which he didn't use) even more apparent.

Luxury cruiser went you want it to be.
Sporty high-performance car when you want it to be.
What a car!

DeerHunter

Nice numbers. 12% drivetrain loss is very good, for any vehicle but especially for one with AWD. Perhaps the Generation VI Quattro (with the Crown gear center differential) is more efficient than previous versions.

At what rpm did he start measuring? I'm interested in whether the torque curve is really as robust off-idle as Audi claims. It's definitely strong, but I'm not sure if it's really making 400 lb-ft at 1,400 rpm unless it's in top gear, traveling up-hill, pulling a loaded trailer.

cagambler

The graph starts at 2250 rpm and goes nearly vertical to about 400 ft-lbs at 2500 rpm. My California version is extremely lean in those first 250 rims as well.

tenspeed

How was the drivetrain loss measured?

cagambler

I've never been in a dyno shop before and didn't't want to ask too many stupid questions, but I think he took it to maximum power in fourth gear and then quickly shifted to neutral. The measurement seemed to have been based on how (long?) it took to decrease in speed from that point. I'll try to attach a photo of the graph.

RobC

Found the user manual on Dynojet's website and found this for measuring drivetrain loss:

The dynamometer calculates horsepower (positive) by measuring how fast the drums
accelerate. If drum deceleration was measured and graphed, we would be viewing
negative horsepower.

The instructions say to perform a dyno run as usual, and when the motor reaches redline, place the transmission into neutral and coast to a stop.

I'm no mechanical engineer (I'm EE), but in theory this makes sense, but the accuracy is subject to proper calculation of losses from the dyno itself and proper calculation of the kinetic energy at the moment you put the transmission into neutral.

Hopefully someone versed in rotational dynamics could lend a hand here.

cagambler

I'd like to believe DeerHunter's theory that Generation VI Quattro (with the Crown gear center differential) is the reason. It fits well with how advanced the car is in every other way. Of course the dyno may have errors and the operator may affect it by how efficiently he gets it into neutral.

I suppose our alternative is to use the long-time estimate of 20%, in which case the crank HP is 497. I could enjoy that conclusion as well. I could take it back in winter and get an implied number exceeding 500.

By the way, after the testing, the warning light was on for the sport differential. The owner manual describes it as "the transmission temperature has increased significantly due to the sporty driving manner." I stopped for lunch and never saw the indicator again after resuming my drive home.

DeerHunter

Given that the differential depends upon ambient air for cooling, that's not too surprising. Not much air flow to the back of the car on a dyno. It might be an issue for heavy track use, but probably not on the street.

Do you have, or can ask for, the native Winpep Dynojet files? I'd love to plug them into my Winpep viewer and print some power and torque curves (which, of course, I'd share with everyone).

cagambler

I'll ask for them.

mwar99

Would have to probably be really heavy track use. I had no issues with the differential on the track...just too little gas in the tank on the last run...