Engineering Explained Dives Into EV Torque Versus Gas HP

AUG 14 2018 BY DOMENICK YONEY 29

Takes us for some quick rides

When we talk about cars and their performance, the terms horsepower and torque always get tossed about. But what do these terms represent and how do they help us compare the abilities of a gasoline-powered car with an electric one? We’re glad you asked because, in the video above, Engineering Explained host Jason Fenske walks us through this technical minefield using his Honda S2000 and his Nissan LEAF. He then goes on to explain how torque ties in with Formula E.

To help explain the numbers, he does a few accelerations runs in the vehicles, motoring all the way up to 80 miles per hour, taking notes along the way. The LEAF has a lot more torque, but a lot less horsepower and is relatively heavy. The Honda? It has tons of horsepower, but relatively low torque. It’s also pretty light. Despite its inferior power to weight, the LEAF beats the internal combustion competitor to 50 mph. Above that, the Honda shines. Unless, of course, you rev up the little sports car to 5,000 rpm and dump the clutch. Then the Honda is quicker, even at the lower speeds. Confused? Hit play!

Video description:

Because electric cars produce peak torque at zero RPM, you might be surprised by the acceleration they’re capable of, especially at lower vehicle speeds. On the other hand, internal combustion engines need to be spinning up at a much higher speed than electric motors before they produce peak torque, especially engines like the F20C in the Honda S2000 used in this video.

The cars chosen for the comparison are quite different. The Nissan Leaf has high torque, 236 lb-ft, but relatively low power at 147 HP. The Honda S2000 on the other hand has decent power, 265 whp, but low torque at just 163 lb-ft. The engine is designed to make peak power and peak torque at very high RPM, above 8,000, versus zero RPM like the Leaf. The S2000 is much lighter, however. Which vehicle will accelerate faster? I’ve created a simple 0-80 mph test to show how the torque delivery of each vehicle differs.

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29 Comments on "Engineering Explained Dives Into EV Torque Versus Gas HP"

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KevinZ

The bottom line is the amount of torque that you have at the rear wheels.

Kimmo57

The Leaf has zero 🙂

KevinZ

The reason the leaf is quicker off the line is because there is more torque at the wheels. With 236 ft/lbs of motor torque times the 8.19:1 axle ratio, there is 1933 ft/lbs of torque at the axle. While the gas car has only 1024 ft/lbs. (½ of the 163 ft/lbs of torque available at 3,000 rpms times 1st gear ratio of 3.133:1, times the final drive ratio of 4.10:1). You could increase the acceleration by increasing the torque at the wheels by gearing it down with a reduction in top speed. It’s all about the torque at the wheels.

Some Guy

So that must be why the Leaf does 0-60 in 7.4~ seconds and the S2000 does it in 4.9~. Explains everything!
It’s all about power to the wheels.

ModernMarvelFan

You need that torque at the wheel for rpm. So you need a curve of torque vs. rpm.

Tom
Yes, that’s what counts. Motor output power is the product of torque and angular velocity of the motor shaft. Because typical ev electric motors have peak torque from ~ 0 rpm out to 4000 rpm or more, power increases with motor rpm, whereas an ice has peak torque at higher rpm resulting in a “power band” at higher rpm. You can use the motor torque vs rpm curve, “torque-speed curve” to calculate the acceleration vs speed of a vehicle. I did this for the car I converted, and it agreed with measured 0 – 60 mph time to within a fraction of second. You can increase the gear ratio (or use smaller wheels/tires) to get more tractive effort (wheel torque divided by tire dynamic radius) at lower motor rpms, but there is a tradeoff. The motor runs at higher rpm for a given vehicle speed and gets up past “base speed”, where the torque starts to fall off with increasing motor rpm, at lower vehicle speed than with higher gearing. For high starting torque and high power you need a big motor with high base speed. And of course an inverter and battery pack capable of supplying the power. That’s… Read more »
Doggydogworld

Good points. Tesla also has excellent traction control, which is more important for 0-60 than raw torque or power once you get beyond certain levels. They also apply power to the rear wheels, or better yet all 4, which is better for acceleration.

BoltEV (was SparkEV)

It would be interesting if he covered various TMS technologies, but being a Leaf driver, I doubt he would.

KevinZ

The reason for the gain in acceleration when “dumping the clutch” is mostly due to kinetic energy. Energy is used and stored to rev the engine, then released when letting out the clutch.

Henry

Not quite. There is no “kinetic energy” as the car is still stationary prior to “dumping the clutch”. Revving the engine puts it in upper part of the power band so that when the clutch is engaged there is more force/torque available to accelerate the car. In standing start, the engine has very low torque available which take time to ramp up due to moment of inertia of the engine and crankshaft – it can take several seconds to rev up to 6000 rpm or above from a standing start.

There may be some potential energy stored in the flywheel, but not significant. You can simply verify this for yourself: in a car with auto trans, revving up the gas while pressing the brake pedal then releasing both pedals at the same time – this will use only the potential energy stored in the engine – the car will plunge forward momentarily but will not go far.

KevinZ

Potential energy is found in a compressed spring or a pulled back bow and arrow. Kinetic energy is the energy stored in a system in motion such as a flywheel. Flywheel energy storage systems (FESS) employ kinetic energy stored in a rotating mass. The energy is discharged by drawing down the kinetic energy.

Doggydogworld

Yes, flywheel has kinetic energy, which increases with RPM. The same is true for crankshaft and pistons. It’s a tiny amount compared to the energy needed to accelerate a car to 60 mph, though.

Another Euro point of view

Very good video & I understand why they took the Honda S2000 to compare with Leaf as it is a bit of an extreme example because of its torque curve. I don’t know about the US but in Europe due to downsizing efforts many (almost all) cars coming on the market now have a turbo charger. Because of progress in the turbo charging technology they spool up at very low RPM which makes those ICE having max torque at as low as 1500 to 2000 RPM. That is a lot less “efficient” torque wise than a BEV but a lot better than the S2000.

Franco

Yes, but this test is done with the electric motor only having 1 gear. Give the leaf a few more gears and the result would swing even more to the electric motor. Or try to run the gas motor on one gear, no contest.

Ricardo

There is a reason why they only have one gear. The Leaf lost this one. Let it go. Geeez. Some of you guys can’t stand watching even a golf cart losing to a Ferrari can you? The S2000 is a great little car. Say with me. It’s a great sports car. The Leaf was not meant to be one. It’s ok to lose to the S2000. Really, it is. It’s not the end of the world.

Max McCreery

Its very hard to accurately compare apples to apples, unless you have the Honda in one gear that has the equivalent gear ratio to the wheel that the Leaf does. At that point you can measure the real power at the wheels and characteristics of each motor/engine.

One of my favorite descriptions of horsepower versus torque is: “Horsepower is how fast you will hit the brick wall. Torque determines how far you will go through it.”

Senna

He still doesn’t understand to talk about power instead of horsepower. The physical quantity is power. Horsepower is a unit.

Bill Howland

1 Imperial horsepower is 746 watts. 1 metric PS is 736 watts. Both are watts, which are 1 joule/second or the rate at which a fixed amount of energy is being expended. Of all the pig-latin coming from this guy, the use of the word horsepower isn’t one of them.

Your Dad

You clearly didn’t understand his point.

Bill Howland

Uh huh. – more likely you didn’t. English units are the official standard in this country man. Some physical units used by engineers are metric, but unlike my father, I wish they’d stick to English.

Electrical units have always been assumed to be ‘metric’ by Europeans, and lately Americans are using European Names for them, but that traditionally this has not been the case.

The English electrical descriptors to me are easier to use since they tell you exactly what they are measuring:

Examples, Cycles per seconds, MHOs rather than Hertz, Siemens.

Big Solar

put the same gearbox or transmission on both and find out.

philip d

Keep dumping the clutch on that S2000 and see how long it takes you before it’s in the shop. Stomp the accelerator on the Leaf day in and day out and zero maintenance consequences.

Troy

yu’d burn thru ecopias like butter tho

ModernMarvelFan

“Unless, of course, you rev up the little sports car to 5,000 rpm and dump the clutch. Then the Honda is quicker, even at the lower speeds. Confused? Hit play!”

Nothing is confused about that. Torque at given rpm x rpm = power. They are totally related. The problem is that people keep forgetting about key part which is rpm or gearing ratio in this case. Also, both Power (HP) and Torque are functions of rpm. So, a simple number is useless. It needs to be a chart with all the relevant information. A better representation is a chart with curves on them that display hp and torque vs. rpm.

Bill Howland

Haha!!! This guy never fails to entertain me.

I wonder where he comes up with his charts since I see no evidence of any gear shifting in the gas car. The shifts seemed rather lackadaisical besides.

But I can confirm that my 2014 ELR has rather spirited acceleration although having only limited gear ratio adjustment.

Troy

having come from a MY 2000 Miata, the Leaf does feel to me like a V6 car, 0 to 50 at least.

like the S2000, the MX-5 was really laggard below 4000RPM.

Also, the Leaf only has 1 reduction gear, so 92MPH is as fast as she goes.

Max McCreery
HP = (torque x rpm) / 5252 Torque and rpm are real fixed numbers. Power is derived, and in an ICE engine, can be vary variable based on RPM. The Chevy I6 230/250/292 could produce a flat torque curve, which is something very very few ICE engines could, or even can do. it is why it was able to take engines 100 CI bigger than it. The magic is power is a flat torque curve so that rpms don’t matter nearly as much. That is one of the biggest reasons that electric motors can kick so much ass. They join Diesels, and Inline 6’s in performance due to the torque. You don’t have to take time to spin you engine past 3500 rpm to get any real power out of it. its available off the line. The “drop the clutch” thing this guy is doing, is simply taking the engine up into its power band so that he can have strong takeoff power. Yes, he has real power there, but the car’s drivability and the drivetrain components won’t take that kind of abuse for very long. Its not only if you have power, its where you have it. If you… Read more »
F teo

Here we are talking about two complete different methods of generating torque. Most wanted to equate to ICE scenario that they know about but most “assumptions” on the electric motors were wrong!.
First all, force of torque comes from flywheel in ICE car. The crankshaft spins the flywheel depends on rpm of ICE engine which is how it generates power based on combustion.
The EV motor generate torque directly from the spindle shaft (into single gear drive ; reduction gear) from current using voltage as driver. So torque curve for EV is FLAT, it is a maximum all the time!. ICE engine has a curve depending on engine configuration. On the EV motor the spindle rpm is controlled by electronics that manages Volt vs Amp so it does not need many gear but works just like seamless CVT with fixed final ratio. Efficient of motor depends on rpm range while torque remain peak all the time. Without a clutch or chain drive (it is direct gear drive ; oil cooled), EV motors last 3-6X the mileage of ICE engine!.

Bill Howland

HAHA! That sounds like a description of a discussion of the shaft counterweight on a cooling bed at my old steel plant (think of a sewing machine treadle that moves the cloth, just 100,000 times bigger) , an argument resulting from the head millwright and the supervisory engineer (who in my opinion wasn’t that great).

The millwright asked a tongue-in-cheek question: How does the counterweight work?

Engineer: The machine comes around, and then the counterweight kicks in and completes the cycle.

Millwright “If that’s the case, why don’t we get rid of the 100 HP electric motor !!! ???”

The Engineer in this case did not understand optimum placement of the counterweight, which was adjustable the full 360 degrees. Since there was no positive brake, only dynamic braking, the counter weight HAD to be compromise located such that the treadle wouldn’t block the incoming steel ‘Logs’.