Horsepower is one of the first numbers we look at when buying a new car. But what does it actually mean? And is there a way to work out how much HP your car has?
Here, we’re taking a deep dive into horsepower, covering what it is, how it’s measured, and ways to calculate how much horsepower your engine develops.
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Horsepower is the metric used to show how much power an engine produces. It stems from the 18th century, when Scottish inventor James Watt coined the phrase to help market his new range of steam engines.
At the time, horses remained one of the primary sources of power for early machines, such as grain mills. So, to attract the attention of potential investors, Watt dreamt up a way of measuring how much power his machines produced in relation to the good old horse – demonstrating the efficiency and work rate of his invention.
This is where explaining horsepower gets more complicated. In fact, the calculations are only really used by mathematicians.
In layman’s terms, horsepower is defined as: the power needed to move 550 pounds one foot, in one second. This is in relation to how much weight a horse can lift, which in Watt’s time was typically around a quarter of a tonne.
Really, all you need to remember is that HP is a measurement of the rate at which power is generated.
While HP remains the standard means of demonstrating a car’s power and performance, torque is often cited alongside it – but how do the two differ?
Put simply, horsepower is a work rate metric, while torque is a measurement of how much power is needed to do that work. This is perhaps best described through the following:
Say you’re accelerating on a stretch of road from 0-100mph. Torque measures the required force needed to get the car moving, while horsepower represents the speed at which the car can reach its target speed.
That’s why some cars with less horsepower can rival others when accelerating from a standing start. They may have more torque (or weigh less) but may not be able to accelerate as quickly to a maximum speed, which is what horsepower helps with.
If you do want to work out roughly how much horsepower your car produces yourself and know your car’s torque, you can use this formula:
Horsepower = Torque x RPM / 5,252
So, say your car has 91Nm (Newton-metres) of torque and a maximum RPM of 6,200. Multiplying the two together gives 564,200; divide this by 5,252, and you get 107 – which is roughly how much HP the engine generates.
Oh, and if you’re wondering what ‘5,252’ represents in the equation, this is the ‘meeting point’ of torque and horsepower in RPM. Without going into the physics, it’s the point at which horsepower equals torque, which is why it’s always used in the formula when working out an individual car’s total horsepower.
Calculate Your Car’s Horsepower in three Steps
Back to calculating your car’s horsepower, then, and using the formula above makes things pretty easy. Here’s how to do it:
- First, dig out your owner’s manual which will tell you your car’s maximum torque. Make a note of it before proceeding to the next step.
- Next, jot down your car’s maximum RPM. You’ll have to go off your car’s rev counter, though the real-world figure may be lower.
- From here, it’s time to get your calculator out and do some sums. Remember, you need to multiply the total torque by the maximum RPM, before dividing that figure by 5,252 to arrive at your car’s horsepower.
Of course, this isn’t the most accurate way of measuring horsepower, but it’s a nice way for everyday drivers to get an idea of what their car is capable of.
If you want to calculate your car’s maximum horsepower within a close degree of accuracy, you’ll need a lot of specialist tools and equipment, including an engine stand or rolling road. Given that such equipment is out of reach of the standard car enthusiast, the above method is a simple and practical way of getting close to your car’s horsepower figure.
There are a few different ways to increase or restore a car’s horsepower, from basic fixes to advanced engine tune-ups. If you want to eke more power from your car, here are a few things to try:
- Use fuel additives – fuel additives and system cleaners are designed to clean and refresh the engine, ensuring that it burns fuel as efficiently as possible. If you’ve never done this to your car, it’s a good way to restore horsepower and performance.
- Regularly clean the air filters – an annual service may not be enough to maintain your car’s peak performance throughout the year. A simple way to ensure your engine is running at its best is to regularly clean out the air filter with an air line.
- Install a turbocharger – while you may not be able to fit a turbocharger yourself, it’s a great way to increase your car’s overall torque, horsepower, and performance.
- Have the engine professionally tuned – an effective way to gain extra performance from your car’s stock engine is to have it professionally tuned. Specialist mechanics can tweak the setup of your engine to increase horsepower, adjusting the ECU to maximise power.
We hope this guide has shed some light on horsepower and how it relates to your car’s power output. If you want to ensure optimum health and performance for your car, Redex fuel additives and system cleaners are a great way to clean, maintain and restore the engine. For more information and advice, visit the homepage.