In this article, we will delve into a fascinating comparison between two identical vehicles with different power outputs. One vehicle boasts 1000 horsepower (HP) and 500 pound-feet of torque, while the other has 500 HP and 1000 pound-feet of torque. A common question that arises is, which one would win in a quarter-mile drag strip race? Is it the one with higher horsepower or the one with higher torque? This question leads us to a deeper understanding of horsepower, torque, and vehicle dynamics, and possibly a headache!
To make the comparison fair, we will assume that the peak horsepower and peak torque values occur at the same RPM for both vehicles. For instance, let’s say the peak horsepower occurs at 5000 RPM and peak torque occurs at 2500 RPM. However, there is a catch. One of these vehicles or engines is actually impossible to exist, and to understand why we will use a simple formula that relates horsepower, torque, and RPM.
By the end of this article, you will have a more profound understanding of the relationship between horsepower and torque, and how they affect vehicle performance. We will use a simulation software to compare the performance of both vehicles over a quarter-mile drag strip and under different conditions.
Let’s get started by understanding the key concepts of horsepower and torque, and how they are interconnected.
Horsepower is a unit of power that is commonly used to measure the output of engines and motors. It was originally coined by James Watt in the 18th century to compare the power of steam engines with the power of draft horses. One horsepower is equivalent to 745.7 watts.
In the context of vehicles, horsepower refers to the power that the engine produces. It is a measure of the engine’s ability to do work over time. The more horsepower an engine has, the more work it can do in a given amount of time.
Torque is a measure of rotational force. It is the force that causes an object to rotate about an axis. In the context of vehicles, torque refers to the rotational force that the engine produces. It is a measure of the engine’s ability to do work.
The amount of torque that an engine produces is directly related to the amount of air and fuel that it can burn in its cylinders. The more air and fuel that an engine can burn, the more torque it will produce.
Horsepower and torque are closely related. In fact, they are two sides of the same coin. Horsepower is a measure of the engine’s ability to do work over time, while torque is a measure of the engine’s ability to do work.
The following formula can express the relationship between horsepower and torque:
Horsepower = [ Torque (lb-ft) * RPM ] / 5252
This formula shows that horsepower and torque are directly related. As the torque produced by the engine increases, so does the horsepower. Similarly, as the RPM of the engine increases, so does the horsepower.
Both horsepower and torque are important for vehicle performance. Horsepower is important for achieving high speeds, while torque is important for acceleration and pulling power.
In summary, horsepower and torque are two sides of the same coin. They are both measures of the engine’s ability to do work, but they are important for different aspects of vehicle performance. Horsepower is important for achieving high speeds, while torque is important for acceleration and pulling power.
In this experiment, we start by selecting a vehicle, an ’84 Honda CRX. Once the vehicle is selected, the rest of the data gets auto-populated. We then choose a 2.2 liter, street-oriented, 4-cylinder engine. However, this doesn’t matter much as we will define custom horsepower and torque values and curves in the next window.
We input our peak horsepower, its RPM, and our peak torque and the RPM at which it occurs. Initially, we start with a torque-biased engine to see what it can do. To simplify our comparison and keep the focus on the engine, we choose a direct drive transmission, meaning the engine is directly driving the wheels with a 1:1 gear ratio, essentially eliminating the transmission from the equation. We are comparing the engines and their horsepower and torque to see what kind of performance they can generate over a quarter-mile drag strip.
For the tires, we choose stock street tires and wheels, a conservative driving style, and typical track conditions.
The result for our torque-biased engine is 13.6 seconds. Next, we test our horsepower-biased engine, keeping everything the same except for the horsepower and torque. The result is 19.4 seconds, which is significantly slower despite having 1000 horsepower. This teaches us an important lesson: horsepower and torque are interconnected. If you have high horsepower but disproportionately low torque, your performance will be subpar.
As observed in the graphs, our vehicle never even manages to reach 100 miles per hour. It launches at around 4000 RPM, but the RPM immediately falls off. There simply isn’t enough torque to sustain the desired RPM.
To make our vehicle more realistic, we introduce gear ratios into the game and choose a normal street final drive ratio of 3:1. This means we multiply the torque by three times and reduce the output rotation speed also by three times. With a final drive ratio of 3:1, the quarter-mile time of our horsepower-biased engine becomes a very respectable 11.9 seconds. Our torque-biased engine does it in 11.8 seconds, making the race extremely tight.
However, observing the graphs, we learn that the torque-biased vehicle is barely winning due to a complete lack of traction. The tires are practically spinning the entire time, indicating that the torque-biased vehicle has too much torque, overpowering the tires and breaking traction.
To improve traction, we choose mild race tires. This results in wheel spin only half the time and improves our time to a very respectable 10 seconds flat for the torque-biased engine. The horsepower-biased engine, with zero wheel spin, improves to 11.1 seconds but is still slower than the torque-biased engine because it still has too little torque.
We then introduce a proper transmission in addition to a final drive to see what happens. We choose a basic four-speed manual, and our time improves to a very respectable 9.7 seconds for the horsepower-biased engine and 10.4 seconds for the torque-biased engine. The horsepower-biased engine wins now because, with the torque multiplication from the gears of the final drive and the transmission, it can finally make use of its 10,504 RPM.
We then imagine a scenario where the owner of the CRX is using their car to build a house and has loaded the car up with a lot of bricks, making the car weigh 6,000 pounds. Now, our torque-biased vehicle manages a time of 12.4 seconds, and our horsepower-biased vehicle manages a time of 12.8 seconds. Torque wins again.
To exaggerate the effect of weight on performance, we remove the torque multiplying effects of the transmissions and return everything to a 1:1 gear ratio. Now, the horsepower-biased engine does 35 seconds, and the torque-biased engine does 24 seconds, resulting in a 9-second difference.
The experiment yielded several key insights into the relationship between torque, horsepower, and vehicle performance.
The first and most important observation is the interconnectedness of horsepower and torque. Despite having 1000 horsepower, the horsepower-biased engine performed significantly worse than the torque-biased engine, taking 19.4 seconds to complete the quarter-mile compared to the torque-biased engine’s 13.6 seconds. This indicates that having high horsepower but disproportionately low torque results in subpar performance. The vehicle with the horsepower-biased engine never even managed to reach 100 miles per hour, and the RPM immediately fell off after launching, indicating that there wasn’t enough torque to sustain the desired RPM.
The introduction of gear ratios into the experiment highlighted their importance in vehicle performance. Gear ratios are essentially torque multiplication devices. A 3:1 final drive ratio, for example, multiplies the torque by three times and reduces the output rotation speed by three times. With a 3:1 final drive ratio, the quarter-mile time of the horsepower-biased engine improved significantly to 11.9 seconds, while the torque-biased engine completed it in 11.8 seconds. This made the race extremely tight, indicating that with the proper gear ratios, a horsepower-biased engine can perform almost as well as a torque-biased engine.
The experiment also highlighted traction issues. The torque-biased vehicle experienced a complete lack of traction initially, with the tires practically spinning the entire time. This indicated that the vehicle had too much torque, overpowering the tires and breaking traction. This issue was partially resolved by switching to mild race tires, which improved the quarter-mile time to 10 seconds flat for the torque-biased engine and 11.1 seconds for the horsepower-biased engine.
The introduction of a proper transmission, in addition to a final drive, further improved performance. With a basic four-speed manual transmission, the horsepower-biased engine completed the quarter-mile in 9.7 seconds, while the torque-biased engine took 10.4 seconds. This result indicates that with the right transmission and final drive, a horsepower-biased engine can outperform a torque-biased engine.
Finally, the experiment demonstrated the effect of weight on performance. When the vehicle’s weight was increased to 6,000 pounds, the torque-biased vehicle completed the quarter-mile in 12.4 seconds, while the horsepower-biased vehicle took 12.8 seconds. This indicates that torque is more important than horsepower for heavy loads. When the torque multiplying effects of the transmissions were removed, the difference in performance became even more pronounced, with the horsepower-biased engine taking 35 seconds and the torque-biased engine taking 24 seconds to complete the quarter-mile.
The experiment demonstrated that both torque and horsepower are crucial for vehicle performance and that finding the right balance between the two is key. While a torque-biased engine may perform better under heavy loads, a horsepower-biased engine can outperform it with the proper transmission and final drive. Ultimately, the key to optimal performance lies inis selecting the appropriate transmission, final drive, and tires for the vehicle’s intended use.