What is Brake Horsepower and other engine power questions answered

For decades now, manufacturers have waged war on the topic of who’s car is on top when it comes to power.

Whilst perhaps not quite as important anymore as a stellar Nurburgring lap time, the power of a car’s engine still plays its part.

However, depending on where you look, as well as which part of the world you reside in, how a car’s power is calculated will vary, and often be confusing.

Let’s dig into the details and hammer out the finer points of all this talk of horsepower vs brake horsepower, and everything in between.

How did ‘horsepower’ come about?

The term horsepower arrived during the industrial revolution (so, some 200 years ago). Famed Scottish engineer James Watts introduced the notion of comparing steampower to that of a horse.

Watts went on to create a direct comparison between steam locomotives and a horse, with the prevalence of the former starting to rise in the logistical corners of the world.

Though other methods of formulating power from an engine have begun to take over in certain parts of the world, horsepower as a unit still plays a big part in the likes of the UK and the US.

What is Brake Horsepower (BHP)?

If you’re a driver in the UK, then you’ll likely be well-versed with the term ‘brake horsepower’ – or BHP – as it remains the standard form of measurement for engine power (just about).

A core reason for the use of brake horsepower likely comes from that it determines the actual usable power that can be put onto the road. This means that BHP is taking into account all the power lost via friction within the various mechanical components that an engine’s power comes into ‘contact’ with.

Parts such as the transmission and other drivetrain components play a part in the eventual output of an engine, so with brake horsepower it’s deemed only fair that such factors are considered.

Additionally, it’s important to keep in mind that, while a higher engine output in regards to horsepower will result in more power, it doesn’t necessarily mean that the car in question will be faster than another vehicle with less BHP (or any other unit of power).

This is due to factors such as a car’s weight and aerodynamic qualities that can affect such matters.

Horsepower (HP) v Brake Horsepower (BHP)

As already explored, BHP takes into account all of the factors that result in an actual, usable amount of power – when it comes to HP, this isn’t quite the case and is where the two differ in how they are measured.

As the primary unit of power in the States, HP only considers the power generated by the engine itself, and does not factor in how much of that power actually makes it onto the road.

As such, for the same car with the same engine, you’ll see a higher output in HP v BHP due to the former not going beyond the engine block when being calculated.

Put simply, HP is an overall measurement of engine power, while BHP focuses on the power making it to the wheels that is propelling the car.

How is Horsepower measured?

The most typical way to measure the horsepower of a car is via a mechanism called a Dynamometer – perhaps better known as ‘dyno’.

There are many calculations involved to get as true a figure as possible, including such factors as torque and wheel horsepower (WHP), working on the basis that some power will be lost through the drivetrain.

In the world of tuning, getting a car on a dyno is a potentially expensive but very important part of the process, with car owners looking for that all-important power lift after having modifications installed on their pride and joy.

What does PS mean in cars?

This is where this conversation starts to get slightly confusing for some, with varying parts of the world embracing different units of measurements when it comes to the power of a car.

PS stands for ‘pferdestärke’, which effectively just means horsepower, albeit a version of HP that brings it more in line with modern day thinking.

Europe is where you’ll find PS used quite commonly and is seen as a metric version of horsepower as a standard measurement for when cars are advertised.

Much like HP v BHP, PS will always come out as a little higher than imperial-based horsepower, with 1ps working out to 0.986hp.

What about kW in cars?

Going back to our friend James Watts, the watt is named in his honour, and the kilowatt (kW) is an extension of this.

As a unit of power in the International System of Units (SI), a single watt measures energy transfer over time (1w being equal to that of one joule per second), and is a measurement used by engineers the world round as part of the metric system.

Found mainly in territories such as Australia, the kW (1,000w) is a more modern take on engine power, and its usage will no doubt increase as electric vehicles become more and more commonplace.

When it comes to power figures for a car, you’ll notice that the kW figure will be a touch lower than that of the HP output, with 1kW being equal to 1.341hp.