The Torque vs. Horsepower. Horsepower vs torque is a commonly discussed topic in the automotive industry. They’re a prominent emphasis on spec sheets, appear frequently in car reviews, and are heavily advertised. However, few people actually comprehend the distinction between horsepower and torque. Which is superior, and why? Is it better to have more power or more torque for speed and acceleration? This page discusses horsepower, torque, the differences between the two, the significance of the complete power and torque curve, and other topics.
What exactly is torque (TQ)?
The rotating equivalent of linear force is torque. Torque quantifies the force of a twisting motion rather than the force of a straight forward or backward motion. Consider tightening a bolt with a wrench. The specifications are given in foot-pounds (lb-ft) in the United States or joules or newton-meters in the International System (SI).
An engine generates rotational force by forcing the pistons downward, causing the crankshaft to rotate via connecting rods. The torque delivered to the crankshaft then travels through the gearbox, driveshaft, rear differential and eventually the wheels and tyres. To summarise, torque is the ability to perform work.
What exactly is Horsepower (HP)?
Horsepower is a power measuring unit, where power is the rate at which work is completed. The faster a particular force is exerted, the more work that can be done. To generate more horsepower, either increase the twisting force or create the force more frequently.
Engine power is often expressed in Kilowatts (kW) around the world. The next section will discuss the link between power and torque. For the time being, the crucial thing to remember is that power is the rate at which work is completed.
What Is the Difference Between Horsepower and Torque?
TQ is required for HP to exist. Remember that torque is the ability to perform work, while horsepower is the pace at which work is performed. Work cannot be done if there is no ability to do it. Here’s a simple equation that illustrates the link between horsepower and torque:
Torque x Revolutions Per Minute (RPM) / 5252 = Horsepower
Thus, horsepower is simply the torque output multiplied by engine speed and divided by 5,252. This equation is critical for fully comprehending horsepower vs torque. Torque measures how much twisting force you can produce. RPM shows you how many times you can generate that force in a given amount of time. The pace at which work is done (power) can then be calculated after you know how many times the force can be applied in a particular interval.
Internal combustion engines, in the end, produce torque first and foremost. They generate energy from an air-fuel combination. This energy pushes pistons downward, causing the crankshaft to rotate and produce torque.
Consider HP vs TQ further.
I often hear and see a simplistic description of power and torque: torque gets you off the line, while horsepower lets you drive fast. This is a usually correct and straightforward explanation, but it might be misleading if you don’t grasp the true link between horsepower and torque. Let’s look at two quick examples based on the hp vs tq equation:
304.6hp = 2,000 lb-ft x 800rpm / 5252
150 pound-feet x 800 revolutions per minute / 5252 = 22.8 horsepower
Most engines idle at or near 800rpm, and horsepower is almost certainly lower than torque at those rates. Ultimately, horsepower is the ability to perform labour, and that power is what propels you forward. Consider moving a 50,000-pound vehicle from a stop with only 22.8 horsepower.
That is when the part of the statement that torque pulls you off the line comes into play. Again, it is the rate at which work is completed (power) that truly propels the truck forward. Torque is essential, though, because a larger torque value at a given engine speed equals more horsepower. As a result, the 304 horsepower at 800rpm in the first example.
It is also true that horsepower allows you to travel faster. Assuming all other factors remain constant, such as weight, aerodynamics, gearing, and so on. The quicker work is completed, the faster a car can drive.
Torque and horsepower measurements
Another critical point is the distinction between various horsepower and torque measures. The Society of Automotive Engineers (SAE International) establishes standards for measuring and correcting power and torque. Power and torque are adjusted to typical atmospheric conditions to make comparisons more accurate (since pressure, temperature, and humidity can all effect power and torque production). Gross, net, and certified are the three primary SAE metrics.
Gross Horsepower and Torque Ratings from SAE
Prior to 1972, gross power and torque figures were widely used. These power ratings are obtained at the crankshaft without the use of engine accessories such as the alternator, cooling fan, water pump, and so on. Long-tube test headers were frequently installed in place of the OEM exhaust manifold. It’s not an accurate depiction of the engine’s power and torque when fitted in the car.
Net Power SAE
Manufacturers began utilising SAE net power ratings after 1971. The power and torque ratings at the crankshaft include all OEM accessories and parts. In other words, it accurately represents the output as placed in a street-legal vehicle.
Power Ratings Certified by SAE
The SAE introduced a new power and torque standard in 2005. Power ratings must be performed in a certified facility and witnessed by an SAE-approved third party. This ensures that manufacturers cannot influence specific test parameters.
Crank Horsepower (HP) vs. Wheel Horsepower (WHP)
The preceding samples are benchmarks for manufacturers when quoting horsepower and torque. They are, however, not an exact depiction of the output that reaches the back wheels. Because they are all measured at the crankshaft, none of the above SAE specifications account for parasitic drivetrain losses.
Of course, torque must be transferred from the crankshaft to the gearbox, driveshaft, differential, axles and wheels. The phrases wheel horsepower (WHP), rear wheel horsepower (RWHP), and/or wheel torque (WTQ) are likely recognisable to most automotive aficionados.
These tests are carried out on a chassis dynamometer, also known as a dyno. A chassis dyno measures torque at the driving wheels, which might be the front, rear, or all four wheels of a vehicle. This test determines how much power and torque makes it all the way to the ground.
It should be noted that chassis dynos differ significantly as well. The DynoJet and Mustang Dyno are two popular dynos. The Mustang Dyno is also known as the heartbreaker dyno because it is known to read low (and no, they aren’t just for Mustangs – the name is just a coincidence). Then there are adjustment factors to consider, such as SAE and STD. This might be a separate article, so we’ll leave it there for the time being.
Engine Dyno Example of HP vs TQ
A dyno chart with two examples to demonstrate the relevance of the powerband is shown below:
Engine Dyno: Torque vs. Horsepower – What’s the Difference?
Our goal with Car 1 was to simulate a turbo or dual turbo engine dyno. Car 2 represents a huge normally aspirated (NA) or supercharged V8 engine. Turbo engines typically have some turbo lag, which causes torque to begin lower while the turbos build boost pressure. NA or supercharged engines respond faster and generate torque almost quickly, and power is quite linear.
Turbo engines, on the other hand, excel in the mid-range, where they provide enormous torque. Larger turbos often have more turbo lag and perform better on the top end, but that’s a topic for another day. In any case, the turbo engine clearly has the upper hand here. Of course, this assumes comparable weight, gearing, traction, aerodynamics, and the plethora of other elements that influence acceleration and top speed.
Yes, both vehicles have 628 horsepower. If these cars were for sale, they would both boast 628 horsepower. When asked how much power their cars produced, both owners gave the same number. Naturally, they’d round up to 650 horsepower (or 700hp if they had a few stickers), but that’s beside the point.
The Point: It’s All About The Powerband
The purpose of the dyno shown above was not to demonstrate that torque is more significant. Instead, the point is that peak power and torque only tell a portion of the picture. Peak figures simply indicate the maximum power and torque at the specified RPM. Some engines have a narrow powerband, whilst others have a wider powerband.
To cut a long story short, sure, a 600 horsepower automobile can blow the doors off a 700 horsepower car. This is especially true if the lower-powered automobile has better gearing, is lighter, and has other advantages. Similarly, a car with 600 torque can outperform a car with 700 torque.
Finally, power and torque each have their own purpose and are inextricably linked. Without a complete picture, none is inherently better or more significant than the other. That is why, when evaluating engine output, the powerband and torque curve are critical pieces of the puzzle.
Summary of Horsepower vs Torque
Conversations about horsepower vs torque are widespread in the automobile sector. That is especially true when it comes to arguments like, “No, it doesn’t matter if you have 50hp more than me because I have more torque!” Is one measure, however, truly superior to the other?
Torque is the ability to perform work, whereas horsepower is the rate at which work is performed. This is demonstrated by the following simple equation: HP = TQ x RPM / 5252. In other terms, horsepower is calculated by multiplying twisting force by engine speed and then dividing by 5,252. That calculation alone demonstrates how closely horsepower and torque are related.
Finally, the rate of work done (horsepower) is the most striking indicator of engine performance. However, horsepower is determined by torque, therefore higher torque at a particular RPM results in more power. In that respect, it’s difficult to argue one figure is more significant than the other.
Instead, the most important component in horsepower vs torque is frequently the full powerband and torque curve. Peak numbers only represent a small portion of the image. When compared to an engine that can sustain 700 horsepower or torque for a longer period of time, 700 horsepower or torque matters relatively little.