thanks for information

 

it will not be underrated. the engine is going to SAE certified and, therefor, impossible to be underrated.

 

Or (e), a more restrictive air intake.

SAE certification prevents overrating, not underrating.

 

Seen the 08 Vettes dyno? About ~390 is common, with a 15% loss which is commonly used for the T56/RWD platform that's 461 hp.

 

you obviously have not read about the SAE certification process and it's rules. go to their website and check it out. it prevents both underrating and overrating. its +-1%.

 

15% is obviously wrong then. its closer to 11-12%, and maybe even less on high powered engines. There's no way around the SAE certification Horsepower number. check out their website.

 

15% is a ridiculously high amount of drivetrain loss for a T56. That amount may be "commonly used," but only by those who assume that a T56 is no more efficient than a traditional 4- or 5-speed manual.

Also, the '08 Vette uses the TR6060, which is the successor to the T56.

On a stock LS1 M6 F-body, 12-13% loss is typical. As horsepower increases, expect the percentage loss to decrease.

 

It increases for automatic transmissions. We're talking about the T56 / TR6060.

I don't have the data handy, but I've seen proof that 400bhp through a T56 and a 9" yields a higher percentage of drivetrain loss than 500bhp through the same drivetrain.

 

just proportional gains will do that.

and drivetrain losses is different than aero losses.

I have also seen higher hp cars lose less through the drivetrain proportionally than lower hp cars. nothing major, like 2%.

 

I'm not arguing physics, I'm arguing results. As I said, I've seen proof. (IIRC, it came from Injuneer.) If you have data to the contrary, I'm all ears.

 

I got a PM asking if I could stop by this thread and make a comment.

There are three general types of losses:

1) Frictional. This will tend to be proportional to the increase in torque in the gearbox, and the increase in speed.
2) Viscous. These losses increase only with speed, and tend to be much less significant than frictional losses at the sort of loads and speeds that we're talking about with automotive gearboxes (the same might not be true when talking about devices that operate at much higher speeds and much lower loads).
3) Inertial. These losses are proportional to the rate of acceleration, and aren't really "losses" in the sense of talking about steady-state power losses - but since inertia dynos are dynamic in nature (as is real-world driving), they must be considered.

If the viscous losses dominated the measured losses in the powertrain, then it'd be possible that increasing the engine output might result in a decreased in measured losses (just so long as the rotational speed of the drivetrain elements didn't increase). But typically, frictional losses will dominate the measured losses in the powertrain, and so it's highly unlikely that the overall powertrain efficiency will increase with more engine output - in fact, the opposite is likely to occur.

I'd love to see data that shows the opposite effect. I suspect that there are test abnormalities, minor measurement errors, or other changes in the vehicle setup that would make it very difficult to make an apples-to-apples comparison that shows a net decrease in the percentage loss incurred in the powertrain.

Put in simple terms - more power is going to almost always mean proportionally greater losses.

 

Makes sense... I guess I'll have to ask Fred to confirm/deny my memory of his results.

 

My tests - engine dyno vs chassis dyno - showed:

McLeod Street Twin/Steel flywheel/T56/3" CM DS/Strange 12-bolt/3.73:1/17x9.5 OZ wheels w/ 275/40-17 GS-C's:

NA: 486 flywheelHP / 425 rwHP = 12.55% loss

1-stage N2O: 635 flywheelHP / 557 rwHP = 12.28% loss

2-stage N2O: 765 flywheelHP / 672.5 rwHP = 12.09% loss

TH400/5000rpm flash, non-locking converter/3" CM DS/Strange 12-bolt/4.11:1/17x11 ZR1 wheels w/ 315/35-17 BFG DR's:

NA: 486 flywheelHP / 390 rwHP = 19.8% loss

1-stage N2O: 635 flywheelHP / 507 rwHP = 20.2% loss

2-stage N2O: 765 flywheelHP / 602 rwHP = 21.3% loss

One complication.... on an engine dyno, the RPM/sec acceleration can be controlled at a constant value, standardizing the inertial losses. On a DynoJet, a more powerful engine will accelerate faster, increasing the inertial losses.

 

Thanks, Fred. I'm glad to hear that my mind isn't playing tricks on me.

Eric / anyone, does the complication Fred mentioned explain the anomaly?

 

Do you have a better way to measure drivetrain loss than with two different dynos?

True. It's also a very limited data set. There is a consistent trend, however, and I have yet to see anyone post actual results that indicate otherwise.