Tesla LIED to us! (I maxed out a dyno in my car)

[scaesare]

You dyno in whatever gear is direct (1:1) on an ICE, so I'd say it's comparable. What is not comparable is if the dyno operator applied weather corrections (temp, humidity and barometric pressure) to the numbers. Those should not be applied for an electric car and would inflate the numbers slightly. Don't know if they were applied in this case?

Actually, even though you may be in "direct" (or closest to 1:1) on the transmission, on an ICE there's still the gear reduction within the differential that needs to be accounted for to convert back to shaft tq at the motor.

So I think LuigiV's point is a valid one, and in this case because the dyno is being overwhelmed, it's simply displaying the max raw value it read with no conversion.

There are lots of cars that make 400+ ft/lbs of tq.. however a typical differential is only multiplying it by factor of 3 or 4... not nearly 10. So this is where the problem likely is...

 

[GSP]

FYI...I think it's the gear reduction that makes it possible for Chevy to claim the Spark EV has 400 lb-ft. :smile:

Not true. The Spark EV motor makes 400 ft-lb. The axle torque is higher due to the gear reduction. The high motor torque enables a numerically low gear reduction (about 2.8:1). That reduces gear mesh losses and improves efficiency for more EV range.

The P85 2000+ ft-lb number from the dyno is at the wheels.

GSP

 

[zwede]

Actually, even though you may be in "direct" (or closest to 1:1) on the transmission, on an ICE there's still the gear reduction within the differential that needs to be accounted for to convert back to shaft tq at the motor.

True. What can I say... I posted to early in the morning.

 

[L@urens]

Dynojets are known to be optimistic

 

[gaswalla]

These guys got a different result, why?

Tesla Model S Performance - Dyno - 386HP - YouTube

Tesla Model S Cranks Out 428 Horses At The Wheels: Video
although thee guys got similar results

 

[No Tailpipe]

Officially awesome!

 

[AC1K]

Not true. The Spark EV motor makes 400 ft-lb. The axle torque is higher due to the gear reduction. The high motor torque enables a numerically low gear reduction (about 2.8:1). That reduces gear mesh losses and improves efficiency for more EV range.

The P85 2000+ ft-lb number from the dyno is at the wheels.

GSP

this is a quote from GM

“I need to disabuse you of the mistaken notion that this motor has less than 400 ftlb of Torque. The Spark EV motor is designed and manufactured by GM. This motor makes 540 Nm (402 ftlbf) of Torque at stall and out to about 2000 rpm. This is not gear- multiplied axle torque, but actual motor shaft torque.”

taken from this site
Exclusive: GM Exec Says Spark EVs 400lb-ft of Torque No Misprint | Inside EVs

look at the max RPM, only 2000, they have to gear pretty high to make up loosing a lot of that torque, but with the tesla, its 443 torque all the way to 5100 rpm

 

[InTheShadows]

this is a quote from GM



taken from this site
Exclusive: GM Exec Says Spark EVs 400lb-ft of Torque No Misprint | Inside EVs

look at the max RPM, only 2000, they have to gear pretty high to make up loosing a lot of that torque, but with the tesla, its 443 torque all the way to 5100 rpm

What speed does 5100 rpm equate to?

 

[AC1K]

What speed does 5100 rpm equate to?

since the speed is linear (only 1 gear)

210kph = 16,000 RPM (approx)

so 5100 RPM must equate too... 67kph

 

[igotzzoom]

Not true. The Spark EV motor makes 400 ft-lb. The axle torque is higher due to the gear reduction. The high motor torque enables a numerically low gear reduction (about 2.8:1). That reduces gear mesh losses and improves efficiency for more EV range.

The P85 2000+ ft-lb number from the dyno is at the wheels.

GSP

Actually, this is what I found on the official Chevrolet site for the Spark EV:

Electric Motor and Drive Unit

Type:	electric, two-wheel, front-drive, coaxial
Motor:	permanent magnetic drive motor
Power:	105 kW / 140 horsepower
Torque: (lb-ft / Nm):	327 / 444
Final drive ratio 1):	3.87

I'm not an engineer or mathematician. Still trying to figure out how they're arriving at 400 lb-ft. They're claiming a legit 327 lb-ft of output directly from the motor, which is still pretty mind-blowing for as small as the car is.

 

[matbl]

Am I missing something here. For the MS, isn't the engine torque multiplied with the gear ratio the torque of the rear axle? Wheel torque should be quite different?

 

[Red Sage]

Actually, this is what I found on the official Chevrolet site for the Spark EV:

Electric Motor and Drive Unit

Type:	electric, two-wheel, front-drive, coaxial
Motor:	permanent magnetic drive motor
Power:	105 kW / 140 horsepower
Torque: (lb-ft / Nm):	327 / 444
Final drive ratio 1):	3.87

I'm not an engineer or mathematician. Still trying to figure out how they're arriving at 400 lb-ft. They're claiming a legit 327 lb-ft of output directly from the motor, which is still pretty mind-blowing for as small as the car is.

It's a neat little car! Now, if they could remove the rear doors, rear seats, up the battery to 60 kWh capacity, double the HP, and style it properly... They could call it the 2015 Chevrolet Chevette and I'd get one!

 

[stopcrazypp]

I'm not an engineer or mathematician. Still trying to figure out how they're arriving at 400 lb-ft. They're claiming a legit 327 lb-ft of output directly from the motor, which is still pretty mind-blowing for as small as the car is.

The motor is capable of 400 lb-ft, but there's likely a software limiter to limit the peak torque (usually present in most production EVs). It's not that uncommon either (the EV drag racing crowd can easily get 500+ lb-ft from forklift motors, although the rpm limits of those motors are a lot lower).

After the gear reduction however (which is taller in the Spark), what ends up at the wheels is still roughly the same as other EVs.

 

[AndreyATC]

I'm not a Dyno expert, but this does not seem accurate at all
Yes, this car produced such TQ numbers at the wheels, but only because it is equivalent of 1st gear of an ICE
Normally cars tested in 4-5th gear to get 1:1 ratio
Tesla is 9:1, so might as well divide TQ number by 9 to get crank TQ

 

[qwk]

I'm not a Dyno expert, but this does not seem accurate at all
Yes, this car produced such TQ numbers at the wheels, but only because it is equivalent of 1st gear of an ICE
Normally cars tested in 4-5th gear to get 1:1 ratio
Tesla is 9:1, so might as well divide TQ number by 9 to get crank TQ

It's accurate, but not a fair comparison to ICE cars, because most ICE cars redline at around 5-8k RPM's while the Tesla motor goes 16k RPM's. One could in theory put a reduction gear in an ICE similar to Tesla's, but the top speed would then be too low(probably 30-45mph).

 

[scaesare]

It's accurate, but not a fair comparison to ICE cars, because most ICE cars redline at around 5-8k RPM's while the Tesla motor goes 16k RPM's. One could in theory put a reduction gear in an ICE similar to Tesla's, but the top speed would then be too low(probably 30-45mph).

No, it's not an accurate determination of motor torque , because there is no way to get the gear reduction down to a point that the dyno isn't overloaded, and thus it's just reporting it's max value in error. It's not applying any gear reduction calculation as it would be doing for the rear end of an ICE .

 

[qwk]

No, it's not an accurate determination of motor torque , because there is no way to get the gear reduction down to a point that the dyno isn't overloaded, and thus it's just reporting it's max value in error. It's not applying any gear reduction calculation as it would be doing for the rear end of an ICE .

It's definately not measuring motor torque, only wheel torque. Dynos are a tuning tool, and not really for comparing numbers to other vehicles. A great example of this is that since a dyno cannot load an ICE turbo car properly(especially an auto trans car), you can get a really low reading on a dyno, but absolutely kill everything at the drag strip. I have had cars dyno at 600whp with a manual trans, and when swapped in an auto with a loose converter dyno(same dyno, and powerplant) at 300whp, but be a full second quicker in the quarter mile. Obviously that is an extreme example.

 

[matbl]

It's accurate, but not a fair comparison to ICE cars, because most ICE cars redline at around 5-8k RPM's while the Tesla motor goes 16k RPM's. One could in theory put a reduction gear in an ICE similar to Tesla's, but the top speed would then be too low(probably 30-45mph).

Ehm. There is a reduction gear in an ICE. It's called the first gear.
if you measure an ICE on the first gear you will get very similar results.

 

[zwede]

Ehm. There is a reduction gear in an ICE. It's called the first gear.
if you measure an ICE on the first gear you will get very similar results.

Only if you didn't hook up the rpm probe (spark plug clamp). If the dyno knows motor rpm it will calculate motor toque as it will know the effective gear ratio. That's the reason the MS showed 2000+ lbs-ft. No motor rpm available, so the dyno just showed wheel torque (multiplied by reduction gear).

I've dynoed an ICE car in the wrong gear (3rd) to see what would happen and the torque + hp was lower than 4th (1:1) gear.

 

[jthompson]

Cool thread!!!