Exclusive first Model 3 Dyno

[apacheguy]

So using the API data, showing 250 kw maximum power draw from the battery results in 335 HP. Even then, that assumes that power is transferred at 100% efficiency from the battery to the wheels.

335 HP is a far cry from the 396 HP reported by the OP. Can someone explain this disparity?

 

[MountainPass]

Our dyno graph showed 335whp as well. This was at 80% SOC

 

[diamond.g]

So using the API data, showing 250 kw maximum power draw from the battery results in 335 HP. Even then, that assumes that power is transferred at 100% efficiency from the battery to the wheels.

335 HP is a far cry from the 396 HP reported by the OP. Can someone explain this disparity?

Don't dyno's measure torque and then calculate HP? Seems like messed up math, unless something changed like folks were saying (though no one has backed it up with numbers yet).

 

[Mysterylectric]

Don't dyno's measure torque and then calculate HP? Seems like messed up math, unless something changed like folks were saying (though no one has backed it up with numbers yet).

Dynos measure horsepower, as they take the force applied to the roller, and the roller speed, which will never change based on gear ratios, etc. The torque applied to the rollers is in thousands of foot pounds, and the dyno must reverse calculate based on power and gear ratio input. Some dynos can do this, others can't very well. This particular dyno is an inertial type, so the rollers have very little weight, and it measures purely off the force applied. It reads high, so the 393hp we got is optimistic (but we don't know how optimistic, as we haven't been able to rerun the car, as it's been in the shop, unable to charge). August 5th, we are hosting a dyno day, and we will (hopefully) run every model of Tesla available, and be able to see how everything compares on the same dyno, under the same conditions. The difference between the dyno we will be using, and the one shown here, is it uses weighted rollers, and calculates horsepower based on the amount of time it takes to spin them up. It also calculates torque much better, as it has 2 constant inputs (roller speed, and roller weight), and inputting the gear ratio is the final variable needed for proper torque calculation.

 

[Daniel in SD]

Our dyno graph showed 335whp as well. This was at 80% SOC

Finally an accurate dyno plot! It actually matches measured acceleration data.

 

[Swampgator]

335whp is more than a BMW 340i.

 

[Daniel in SD]

335whp is more than a BMW 340i.

True, but you can only put that power down at one speed. The BMW can put it down at multiple speeds

 

[Mysterylectric]

So, I had mentioned back in February, we were going to be setting up a dyno day. It's purely for fun and a "let's see what happens." We are hoping someone gets an AWD and/or performance Model 3 before then, but I am not very optimistic. We will definitely be running Model 3s, and hopefully every variation of Tesla available. If anyone is interested, it will be August 5th, from 10am to 5ish pm, and hosted here on Long Island. Web page is Supercharged Sunday, and for those who had wondered about an uncorked 75D, here's our test on a non-linked dyno:

. This is a completely different style dyno, so the numbers aren't directly comparable to the Model 3 dyno earlier in the year.

 

[voip-ninja]

335whp is more than a BMW 340i.

335 is actually right about where the 340i is at. It measures at around 360-380 at the crank if I remember correctly. German automakers, much like Tesla, are notorious for sandbagging their horsepower numbers.

 

[Knightshade]

Dynos measure horsepower.

Not usually. Instead they measure torque as Diamond G suggested, then derive HP via calculation from the measured torque figure.


How Horsepower Works

What dynamometers actually measure is torque (in pound-feet), and to convert torque to horsepower you simply multiply torque by rpm/5,252

How a dyno measures horsepower | RideApart

The force the bike outputs on the roller is torque

What is a Dynamometer and How Does it Work?

the power produced by an engine, motor or other rotating prime mover can be calculated by simultaneously measuring torque and rotational speed (rpm)

Dyno Testing Basics: Engine Dynos vs. Chassis Dynos

Horsepower is calculated from the torque value.

 

[Mysterylectric]

Not usually. Instead they measure torque as Diamond G suggested, then derive HP via calculation from the measured torque figure.


How Horsepower Works




How a dyno measures horsepower | RideApart




What is a Dynamometer and How Does it Work?



Dyno Testing Basics: Engine Dynos vs. Chassis Dynos

No, dynos do not measure torque. If they did, you’d be seeing numbers in the thousands. They have to reverse calculate the torque using the input gear ratio.

 

[Daniel in SD]

Who cares whether dynos measure torque or horsepower? Why does it matter? Torque at the wheels is a silly metric because it changes depending on gearing. HP = Torque x RPM ÷ 5252

 

[Knightshade]

No, dynos do not measure torque. If they did, you’d be seeing numbers in the thousands. They have to reverse calculate the torque using the input gear ratio.

Pro tip- when dynoing a car you put the car in whatever transmission gear offers a 1:1 drive ratio (or nearest to it for oddballs that don't have a direct drive transmission gear).

Strange you didn't know that...



So anyway you're claiming...literally every website on the internet describing how dynos work is wrong, and you're correct?

I mean, that's kind of weird.

See also all the sources I just provided.

Or these-

Power and Torque: Understanding the Relationship Between the Two, by EPI Inc.

TORQUE and RPM are the MEASURED quantities of engine output.
POWER is CALCULATED from torque and RPM

and

A dynamometer determines the POWER an engine produces by applying a load to the engine output shaft by means of a water brake, a generator, an eddy-current absorber, or any other controllable device capable of absorbing power. The dynamometer control system causes the absorber to exactly match the amount of TORQUE the engine is producing at that instant, then measures that TORQUE and the RPM of the engine shaft, and from those two measurements, it calculates observed power.

(bold added)


Those guys design aircraft, train, and NASCAR engines and parts... strange how they think Dynos measure torque huh?

Or how bout car and driver? I mean, what do they know about cars, right?


Horsepower vs. Torque: What's the Difference? – Feature – Car and Driver

Another issue is accurately quantifying the power and torque from a spinning crankshaft. The tool for this task is an engine dynamometer. While that word means “power measurement device,” in practice the engine’s torque and rpm are measured and its power is calculated using the formula cited above.

(Bold added)

I mean- from a basic physics perspective- a dyno is measuring a twisting force that tends to cause rotation (of either the crankshaft or wheels depending on the type of dyno)... which is the literal definition of torque.

 

[Knightshade]

Who cares whether dynos measure torque or horsepower? Why does it matter?

Well for one I wouldn't trust dyno results from someone who didn't know which one is correct

Torque at the wheels is a silly metric because it changes depending on gearing. HP = Torque x RPM ÷ 5252

So does horsepower... look at your formula- it kind of has to since one number is derived from the other.

This again is why you dyno with 1:1 gearing where possible.

 

[Mysterylectric]

Well for one I wouldn't trust dyno results from someone who didn't know which one is correct



So does horsepower... look at your formula- it kind of has to since one number is derived from the other.

This again is why you dyno with 1:1 gearing where possible.

Funny, because the guys who built the dyno are the ones who say that the dyno measures horsepower based on the speed and weight of the rollers, then calculates torque using the supplied gear ratio input. Check out the video I posted of the 75D, and you will notice that the torque number changes as we manipulate the gear ratio on each run, but the horsepower stays dead consistent. Funny how that works.

 

[Mysterylectric]

Further, 1:1 is only the transmission gearing, and that is used so it removes a variable when running the calculation. There's still a differential that is not even close to 1:1, regardless of what car you are running. I can input a ratio of 5rpm per mph on this dyno, and it will read thousands of foot pounds, and the horsepower will not change, because the roller weight and time to spin them remain constant.

 

[Daniel in SD]

Well for one I wouldn't trust dyno results from someone who didn't know which one is correct



So does horsepower... look at your formula- it kind of has to since one number is derived from the other.

This again is why you dyno with 1:1 gearing where possible.

The only thing you can measure on a chassis dyno is force at the wheels. Everything else is derived from that and the roller speed. I'm not sure what your point is. Torque is force*distance. How can the dyno possibly measure torque when it has no idea what the radius of the cars wheels are or the gearing inside the car? You have to enter those values and the dyno converts the horsepower measurement to torque.
Now, the way the dyno itself measures horsepower could involve a torque measurement internal to the dyno but there are many different dyno designs and if you look at it as a black box it is measuring power.

 

[diamond.g]

The only thing you can measure on a chassis dyno is force at the wheels. Everything else is derived from that and the roller speed. I'm not sure what your point is. Torque is force*distance. How can the dyno possibly measure torque when it has no idea what the radius of the cars wheels are or the gearing inside the car? You have to enter those values and the dyno converts the horsepower measurement to torque.
Now, the way the dyno itself measures horsepower could involve a torque measurement internal to the dyno but there are many different dyno designs and if you look at it as a black box it is measuring power.

If the dyno measures power (HP/kW) then how come @Mysterylectric got a wildly different reading than others? Seems like measuring power would be a pretty consistent thing.

Also has anyone been able to do a dyno pull and get numbers without having to disable ABS?

 

[Knightshade]

Funny, because the guys who built the dyno are the ones who say that the dyno measures horsepower based on the speed and weight of the rollers, then calculates torque using the supplied gear ratio input. Check out the video I posted of the 75D, and you will notice that the torque number changes as we manipulate the gear ratio on each run, but the horsepower stays dead consistent. Funny how that works.

That would be really funny. Since it contradicts literally everything every other source on the internet says about how dynos actually work.

I guess it might explain why their results don't match anybody elses though...they don't know how their own dyno works!

Also funny as it's pretty obvious your results prove you wrong.

The fact the gearing changes your measured result (torque) is proof that that is the figure you are actually measuring

The dyno then computes horsepower by knowing that measured torque figure and the rpm of the motor.

Since HP = Torque x RPM ÷ 5252 the only way the HP number can stay the same if the gearing changes is if HP is computed

(the fact the dyno is measuring torque and rpm, and then calculating HP, is also pretty obvious by the fact the formula is literally written that way- you need to know torque and rpm, and then you can compute HP)



Here's some more folks who actually know how dynos work....

Chassis Dyno Guide - Frequently Asked Questions About Dyno Tests - Hot Rod Magazine


This one includes input from Dynapack, Dynojet, Mustang, and SuperFlow, all of whom actually manufacture dynos.

Inertia dynos extrapolate horsepower output by analyzing the dyno drum’s acceleration rate

Oh look- they measure torque (force on the drum) and compute HP.

How bout a hydro dyno?

A strain gauge may be used to measure the torque reaction between the rotor’s rotating element and a stationary element, then (just like an engine dyno) calculate the horsepower output.

Torque measured. HP calculated.

How bout an eddy-current dyno?

Also known as an eddy-current dyno, this type of dyno controls the brake/absorber using electric current instead of fluid, measuring torque output and calculating horsepower based on a strain-gauge

Oh- this article is also good because it discusses your claim regarding final drive ratio too-and why with proper setup and software, and running the car in the right gear, this largely isn't a problem.

 

[Knightshade]

The only thing you can measure on a chassis dyno is force at the wheels.

Which is a rotating force- which is torque. By definition.

Now, the way the dyno itself measures horsepower could involve a torque measurement internal to the dyno but there are many different dyno designs and if you look at it as a black box it is measuring power.

See my link above. It explains how each of the major dyno systems works.

all of them directly measure torque and rpm, and use those to compute HP.

Everything else is derived from that and the roller speed. I'm not sure what your point is. Torque is force*distance.

Horsepower - Wikipedia

During testing, the output torque and rotational speed were measured to determine the brake horsepower.

Not sure how many sources need to tell you two the same thing before you believe it.

If you'd prefer the actual physics of why you guys are wrong, it's here-
Horsepower of an Engine

If you don't want to dig through the math and graphs, here's the conclusion-

We have seen that the horsepower of an engine is derived from a measurement of its torque. A moment's reflection may convince you that the torque really is the fundamental quantity of interest in measuring the strength of an engine, since it is the torque exerted... that causes the vehicle to accelerate.

(bold added- or to paraphrase, hp (which is calculated from measured torque) sells cars, but torque wins races)