How often have you come across these terms; “horsepower” and “torque”? Whenever you look into the specifications of vehicle acronyms like hp, bhp, and SI units like Newton-meter and pound-feet must have caught your attention. But what do they mean and how do they affect the vehicle’s performance? Let’s talk about these terms.
To start with, the basics of engines say that the chemical energy of dino-juice extracts from the deepest spots under the earth turns into mechanical energy as the fuel burns and turns the engine. The power that comes out moves over to the transmission and then to the wheels. Between this power transaction, there are various losses, and these need to be accounted for while calculating various aspects of vehicle performance. As the old saying suggests "Horsepower is how fast you hit the wall, torque is how far you move the wall", well that’s a completely wrong reference.
Talking about power, BHP or brake horsepower is the term used for the power of an engine. But the BHP value doesn’t take various losses into account. The BHP determines the acceleration and top speed of a vehicle numerically or virtually.
But we talk about HP or horsepower, it is the power of a vehicle with the losses included. Hence one can say horsepower is the final power that comes out of the engine or to the wheels. There are two types of HP in itself, crank HP and wheel HP. And as these words suggest, crank HP is the power at the engine’s end, the power shot from the crankshaft. While the wheel HP is what results in the wheels in real-time.
Now you might be wondering, why does this power related to “horses” in the first instance.
To start with, horsepower or hp is a made-up term. The great inventor of steam engines, James Watt wanted an efficient unit and decided to compare the effectiveness of these man-made engines to horses. He preferred horses over other animals, the automobile was born out of horse carriages, where the animal did all the efforts of pulling the carriage, its occupants, and the luggage inside. Thus, horsepower was defined as the energy equivalent expended by a single horse lifting 33,000 pounds one foot in the air from the surface of the earth in one minute. Besides hp, there are more terms to define power like kW, ps, and more. And these are nothing but the conversion of hp in other metric systems.
1hp = 0.7457kW
1ps = 0.986 hp( ps is German Pferdestärke (PS) or hp in German)
Now let’s jump on to torque, the other important specification of any vehicle. In scientific terms, torque is a measure of a force that rotates about an axis. From tire to crankshaft spinning inside the engine, all of this is done by torque. The SI unit of torque is Newton-meter(or Nm) which is equivalent to pound-feet( i.e. 1 Nm = 1 pound-feet).
Now, an important question is, how horsepower and torque and these values play an important role in vehicle specifications. As we talked about earlier, horsepower is how fast a vehicle goes or its top speed. While the torque accounts for the amount of load you can carry without performance degradation. Petrol engines are rich in power or horsepower, while the diesel engine forte in torque, or also exemplary towing capacities.
Let’s take examples, sports cars like a Porsche 911 packs a 3.0L flat six-cylinder engine pushing out 641-bhp @6500 rpms and 450Nm @1950-5000 rpms. The Porsche 911 is built for high speeds hence the horsepower section has bigger figures. While the “RPMs” mention denote the bandwidth and relationship of power and torque with engine RPMs.
Now let’s take a pick-up truck, built for hauling big loads and even towing trailers and stuff. How about a Ford F-150 pickup, these are pretty popular globally. The Ford F-150 packs a 3.3L V6 pushing out 250-hp and 440 lb-ft of torque. The high amount of torque helps in pulling big loads. So now we are familiar with these terms, you can always check out vehicles and their specifications and help yourself out to figure out how these numbers affect the performance and capability of a vehicle.