Let’s talk about motors and engines. Arguably, they’re kind of important to the driveability of your car or truck. Those of us who have ever had to try pushing a vehicle down the road can attest to how truly wonderful it is to have a different motive source of power than your own two legs. But, an electric motor is not a gasoline engine and it’s not a diesel engine either. They all three are different beasts with different advantages and disadvantages.
The obvious thing people want to know is “how many horsies does she got?” As luck would have it, you can answer this question for any of the three. A Bolt has a 200HP motor. Tesla vehicles have a range but 350HP is one option. I own a 1985 Mercedes that can make 230HP. Which one is faster? Obviously the Tesla leaves the others in the dust. However, what might be more interesting would be to consider the performance of the Bolt vs my Mercedes. Which one wins? Well, the fight isn’t entirely fair as the Mercedes can do 135MPH while the Bolt is governed to 93MPH. So, after 93MPH there is a clear winner (probably the police!) But, what about the 0-60MPH times? A Bolt can do 0-60MPH in 6.5 seconds. This is glacially slow compared to a Model S Plaid but, I assure you, feels quite zippy when you do it in person on a real road. What about my more powerful V8 Mercedes? That goes 0-60 in 8.9 seconds. Wait, the Mercedes has a 30HP advantage and an engine the size of a small bus. Why is it so much slower? Could it be that focusing on horsepower is a bad way to compare different motors / engines? Yes, it could be and is a poor comparison.
You see, horsepower is one of those things that sounds like it’s just some formless unit engineers made up to annoy people. However, in fact it has more lurking in the shadows. A horsepower can be defined a few ways but the mechanical definition is 746 watts if you mean imperial mechanical horsepower (and this is ‘Merica damn it!) But, more importantly for this discussion, horsepower is (torque * RPM). This is glossing over the fact that you divide this by a set factor. But, this factor is a constant and so doesn’t affect the discussion. So, double the torque and you double your HP. Double your speed and you double your HP. This means it’s a bit meaningless to say “it’s got 400HP!” No, it doesn’t, not all the time. In either an electric motor or an internal combustion engine there is a maximum amount of torque you can generate at any given moment. So, your output HP is always going to be relative to the torque you can provide multiplied by rotational speed of the motor. Both combustion engines and electric motors tend to use gearing for an important reason – it’s easier to spin faster in a smaller motor to get your HP instead of directly generating more raw torque. This is why a Tesla motor can spin up to 16k RPM. This is much easier than trying to build a motor that can spin 1.6k RPM directly to the wheels with the same power. So, the Tesla Model S uses a quite high ratio of around 9.7:1. This keeps the motor small and light (comparatively) while still allowing for high peak power.
But, there are two elephants in the room. It’s quite crowded in here now! The first elephant is called “gas engines don’t have such great torque at low speed”
This is ultimately why the kid in the beat up rust box next to you is revving his engine at the light. He needs the RPM to get any sort of power at all. Meanwhile, an electric motor has all of the torque it will ever have right up front. At 5 RPM it basically has just as much torque as it will have at 1000RPM. This goes a long way to explain why a 200HP Bolt motor can make a 230HP V8 look like a pile of junk in a race from 0-60MPH. The V8 has two disadvantages. First, it doesn’t generate its full power until it has revved up a bit and secondly, it has to shift. Ultimately shifting is necessary in cars with combustion engines because they have a somewhat limited window where they generate a lot of power. Notice how the torque of the gas engine drops even faster than the torque of the electric motor. Engineering Explained covers this quite well (though the S2000 actually keeps its torque very well!)
So, what’s the second elephant in the room? Here is a Chevy Bolt Motor:
Note that this has the gearbox on the end. It weighs around 167 Lbs / 76kg which is isn’t light but lighter than me. This is what a 200HP electric vehicle motor looks like. Meanwhile, this is what a 200HP industrial motor looks like:
How much would you estimate that little guy weighs? 500 lbs? Nope! 1000lbs?! No. A ton?!! NO. It weighs 3004 pounds. Yes, 1.5 tons. So, why is the industrial motor 17 times the weight of the EV motor of the same rated power? Well, two reasons. 1: Nobody cares what an industrial motor weighs. If your forklift can lift it then it’s light enough. 2: That industrial motor can be run at 200HP all day, every day, all year, every year. That EV motor? 200HP is quite an imaginative number. Can it do 200HP? Well, for a while. But, advertising it as 200HP is like saying I could flip a 200 pound tire. Yes, I probably could… once. Maybe twice. Certainly not all day. And, so it is with motors in electric vehicles. Yes, they can do their rated power for a while but the more you push them, the more they heat up. This also is something to keep in mind while comparing electric to gasoline. A 200HP gasoline motor can more or less do 200HP until you run out of fuel. As such, when doing EV conversions, it bears mentioning that electric motors tend to have two values of importance when it comes to peak power. There’s the “geewhiz, if you floor it you can get this much power!” figure and then the “if you drive 100 miles down the road you can expect to maintain this level of power” figure. This figure is much more conservative. Take, for instance, the UQM PowerPhase 100 that we sell. As you might guess, it is 100kW peak power. The continuous rating is instead 60kW. This is not bad either but it’s not 100kW. One thing EV motors do have going for them is liquid cooling. With liquid cooling you can make motors far smaller than they’d otherwise be. Apparently 17x smaller! Even Tesla motors cannot beat physics. Many people have found that racing a Tesla on the track is fun right up until the motor goes into thermal limit. Ultimately a Tesla Plaid may generate more than 1000HP for a few runs but you are not going to be towing cross country a semi-trailer loaded with 40,000 pounds of hamburger.