What Is Peak Engine Horsepower? (And Why Keen Drivers Will Want To Know It)

Horsepower is often one of the first statistics mentioned in the same breath as a car's make and model, especially within performance circles. It's quite an important number, to be certain; the bigger the number, the faster you go, generally-speaking. Usually manufacturers tout one single number on the model's page: "X-model features an engine with over 1,000 horsepower," for example. But horsepower itself is measured in one of a number of different ways, each producing its own individual outcome. You have terms that seem obscure or daunting to the layperson, such as shaft horsepower, SAE net horsepower, brake horsepower, nominal horsepower, and so on, each producing different numbers. In this article, we'll discuss one of the most commonly used formats — an engine's peak horsepower.

So, what does this mean and how does it relate to all these other formats? In short, peak horsepower indicates the speed at which your car produces the most power it possibly can. Let's say your engine produces 500 horsepower; the peak horsepower relates to when your engine actually makes all 500 of that horsepower. Now, calculating horsepower in the first place is a whole separate discussion involving dyno tests and mathematical formulae relating to torque output versus rpm, and horsepower can get affected by external factors like air density, fuel type, and so on. So, let's keep it simple and stick to the raw output number.

Let's focus on typical internal combustion engines here; electric motors feature an entirely different means of measuring power output. So you take your car to get your horsepower measured, and come back with a graph showing at least two lines: horsepower and torque. The horsepower line typically resembles a mountain, always peaking past the torque curve. This is known as your power curve, and the very peak of this curve is your peak engine horsepower. This is measured not just by the actual horsepower number, but also the rpm at which it occurs.

All engines feature a maximum allowed RPM limit, let's say 7,500 RPM in this example. Now, this engine will not produce its maximum power (let's say 500 horsepower) at 7,500 rpm, rather it produces this number at, say, 6,800 rpm. Therefore, the peak horsepower is 500 horsepower at 6,800 rpm. This is vital in a wide variety of motorsport disciplines because it tells the driver and engineer where the power is. The closer an engine operates to its peak horsepower's rpm, the more horsepower it produces.

Let's take land speed record running as an example. Your car hits a certain speed, but you know it has more to give because engine rpms are outside of the power, either too high or too low. Instead of producing all 500 horsepower, your engine's current rpm limits it to just 450 horsepower. So you tune the gears in such a way that as you hit the top speed, you're right at your peak horsepower, giving your car all its available power and making it go faster. This carries over to any regular non-electric car, which is why your car feels far peppier when it's sat in the mid-high rpm range.