To speak knowledgeably about automobiles you should understand the difference between torque and horsepower because they truly measure different things.
Let’s start with HORSEPOWER. Power is the measurement of how much work a given device can do under specific circumstances. If something is more powerful it can do more work. There are multiple ways to measure distance such as meters or miles or inches or feet. Depending on how large something is one of these scales might be better to use than any other, but each would measure distance. Work is the same way. There are multiple ways to measure power and Horsepower is simply one of them.
A long time ago when they divided things up they may well have used their actual foot to scale a specific measurement. Unfortunately one man’s foot might be smaller than another man’s foot, or larger, but rarely would it be exactly the same. So they came up with a standard foot. Three of which made up a yard, and when divided by twelve produced inches.
Horsepower is to measuring work just as a foot is to measuring distance. It is a standard. Surely at some early time the pulling power of an average horse could be used to be pretty close, but eventually horsepower had to be standardized so that today a single horsepower can do exactly the same work as 745.7 watts. That still does not tell us much about how much power a horsepower really is, but most of us do understand that a 60 horsepower engine produces twice the power as a 30 horsepower engine.
At first glance then it might seem like adding more horsepower will make a car go faster. Sometimes, of course, it will, but sometimes it will not.
Here is a silly little example: Suppose you decide to dig a hole in your back yard so you can put in a pool. Almost as soon as you start digging you find that there is one very large bolder in your yard and it will have to be removed leaving a perfect sized hole for the pool. An expert of some kind assures you the bolder weighs exactly a thousand pounds. You go to an equipment rental place to rent a crane. They have two cranes for you to choose from. One can lift up to ten-thousand pounds and it rents for $500 per day. The other can lift up to a million pounds and rents for $25,000 per day. Which one do you rent. Well, obviously either is strong enough to do the work so you rent the less expensive model. You do not need enough power to lift a million pounds, just a thousand.
So, how does that relate to automobiles? Power is not the only consideration for how fast a car can go. Weight is also a very important factor. So if you can add a more powerful engine, one with more horsepower, you also must consider how much more that engine might weigh and also how much more fuel will you have to carry on-board, and how much does the fuel weigh?
So we can see that Horsepower is a simple measurement of the power a given engine could produce, but it alone can not be used to determine how fast it will make our car go.
Torque is an entirely different type of measurement. A dictionary definition for torque would be the measurement of a force or system of forces tending to cause rotation. The key to that definition is where it says “force or system of forces”. That means that it is not looking only at the power required but other things like distance, time, and gearing. If the torque you are measuring is the torque on your rear axle of your car with the tires that are on the wheels, then you can be assured that as you increase the torque you are increasing the speed the car can go. But the measurement of torque implies that you have done all of the other math. For instance, if you are selling a car and it comes with a standard six cylinder engine or you can also get it with an upgrade eight cylinder, and you list the torque, you would have to list how much torque the six would produce in the car as is, and then also list the torque the eight would produce even though it weighs more. You would have to calculate the added weight in to give an honest measurement of the torque.
Of course, calculating torque is much more complicated than calculating power. Even the way it is reported. Whereas power can be reported as a single element, such as horsepower, torque is reported as a complicated ratio of feet/pounds. To explain feet/pounds let’s go back to that silly example. Let’s assume that you, an average man can lift two-hundred pounds. That means that instead of renting a crane you could get yourself and four of your average friends and simply lift the boulder out. But if you were alone you could not do that.
But what if you used a lever? You know, stick a really big, strong, long pipe under it and then go to the end and press down… As you can imagine, the further you go along the lever away from the boulder, the less strenuously you have to press to lift the thousand pounds. How many feet along the lever do you have to be before your 200 pound lifting power is enough using the lever to lift the thousand pounds? Complicated, you bet.
So how do we sum this up? If you want a bigger vehicle with more bells and whistles you are probably going to need more horsepower and your fuel costs will be correspondingly more as well. On the other hand, if you want a faster car change the torque by increasing the horsepower, OR reducing the overall weight of the vehicle including passengers and cargo, OR increase the gear ratio by putting in a more expensive racing transmission, OR even all three.