Torque versus horsepower Archives

How to Read a Dyno Chart

A dyno chart shows an engine’s character.
From it, we can determine if the engine is torquey or peaky.
Please also read Torque Versus Horsepower: What’s the Difference.

A dyno chart – a graph which shows the engine’s torque and power curves – gives us an idea of how the bike performs when we open the throttle.

But how do we interpret those two lines? Do we only look at the peaks? Or just the peak horsepower?

Let’s use the chart below as an example.

The X-axis (the horizontal line below) represents engine RPM, the left Y-axis shows the engine’s horsepower, and the Y-axis on the right represents the engine’s torque.

2018 Ducati Panigale V4 S dyno chart – Credit motorcycle.com. The little dips in the curves denote gearchange

The curved line which climbs the highest is usually the horsepower, while the line below is usually the torque. Why “usually”? Because high torque engines like those big V-twins on Harley-Davidsons, Indians and other cruisers typically produce more torque than horsepower.

In any case, the torque curve is usually flatter than the horsepower curve as the latter requires the engine to be spun up and increases in a steeper curve.

Read: Torque versus Horsepower: What’s the Difference

So far so good?

Okay then, what do we look for? Or more specifically, how do we “read” an engine’s character?

Referring to the graph above, the torque curve looks like a plateau and is considered “flat.” There’s already 86 Nm of torque available at 4,750 RPM, while the peak of about 118 Nm is delivered at 11,250 RPM. Thus, the dyno shows that the engine is already producing 73% of its maximum torque at 4,750 RPM.

We can therefore deduce that this engine will give the impression of power everywhere in the engine range. In the real world, opening the throttle at any time will punch the bike forward rather than needing to be revved like crazy. An engine which allows for hard acceleration anywhere in its rev range is called “torquey” (although most people will wrongly say “powerful”). For the rider, he doesn’t have to keep shifting gears to get going.

As for the horsepower curve, you can see that’s linear in its progression and that makes for easier riding because the bike doesn’t bog and blast forward suddenly as if hit with a NOS injection.

Another thing to note is how many RPMs separate peak torque and peak horsepower. This Desmosedici Stradale V-four’s torque peaks at 11,250 RPM while horsepower does so at close to 13,250 RPM. That gives us 2,000 RPM of separation between the two. This is good as while the torque tapers off, the engine continues to produce power. This is what we call a wide powerband.

However, if the two peaks are close together like in a two-stroke (as little as 500 RPM separation), the powerband is considered “peaky” or “thin.”You need to rev the engine to high RPMs and maintain that high RPM for acceleration. Dropping out of that certain RPM range means you’re stuck with no meaningful acceleration unless you work that left foot like a Riverdance performer.

Note here that four-stroke racing engines tuned for outright power can be peaky. It’s not much of a problem at the racetrack but it’s irritating when such an engine character is present on a road bike.

This is why cruiser riders swear by their engine’s torque as the bike accelerates anytime in any gear, as well as being relaxed (turning at low RPM) when er… cruising down the highway. However, the engine begins to run out of breath as it reaches peak torque, since there’s not enough horsepower to produce higher speeds.

Harley-Davidson Fat Bob dyno chart – Credit cycleworld.com

Lastly, there’s another thing to note. Notice that the dyno’d torque and horsepower figures are lower than claimed by the manufacturer. That’s because manufacturers use bench dynos that are fitted directed to the engine’s output shaft thereby reading the crankshaft torque and horsepower. Dyno-ing a bike through its rear wheel results in approximately 15% power loss through the transmission, final drive and tyre. So, don’t panic if you see lower figures if you dyno your bike.

Torque Versus Horsepower: What’s the Difference?

Engine torque and horsepower are often confused.
Torque is associated with “pick-up” while horsepower is seen as the pre-requisite for top speed.
But those perceptions really the case?

Most of us are transfixed by the word “power” or more specifically, “horsepower.” We even assign the word to other aspects of life such as food i.e. “That laksa lemak was power!”

But an engine produces not only horsepower but torque, as well. This is where it all breaks down. Ask around and you’d probably get different answers. What exactly is horsepower? How is it related to horses? What is torque then? If lots of torque is for hard acceleration, why do we need horsepower? And if lots of horsepower is for higher top speed, why do need torque?

We’ll answer those questions in layman terms.

But first, we need to understand the definition of energy.

What is energy?

Energy is the capability to do work. There are many forms of energy such as chemical energy, potential energy, heat, kinetic energy, mechanical energy, etc.

Where do we get energy from in an internal combustion engine from the exploding air-fuel mixture, of course. It turns the chemical energy stored in the fuel to heat and kinetic energy, and the expanding pressure forces the piston down.

Therefore, energy is expended, and work is done.

Read: How Does a Four-Stroke Engine Work

What is torque then?

Let’s imagine that we’re lifting weights in the gym.

That force we lift them by pivoting our forearms is the torque. In other words, it’s the force through a direction. Torque measures the force of an object as it rotates around an axis, fulcrum or pivot. When we switch to heavier weights, we need more torque to lift them.

In the engine, as the piston is pushed down after air-fuel combustion, it generates forces that turn the crankshaft and flywheel attached to it i.e. torque. It is then channeled through the gearbox, and finally out to the final drive to turn the rear tyre.

Torque can be manipulated by gearing to amplify or reduce its effect – that’s exactly what the transmission is for.

Think of torque as that sheer force generated when the air-fuel mixture combusts inside the engine.

So, what is horsepower?

Power is defined as the rate of the energy being expended or the work is done.

Let’s go back to lifting weights. The faster we lift, the more power we expend. At the same time, we decided to measure how many lifts we could do per second. This rate is measured by Joules per second, which written in the simple term as Watt (W). This is why you often see engine power rated as “kW” (Kilowatt).

Going back to the engine, power is how fast the torque is produced on a timed scale i.e. crankshaft revolutions per minute (RPM). Hence, power is torque multiplied by RPM. In other words, you have to spin the engine faster and faster to receive more horsepower.

But how did “horses” come into play? The unit was coined by Scottish engineer James Watt (remember Watt earlier?) to compare the output of steam engines with the power of horses. From that, 1 mechanical horsepower was derived from a horse lifting a 550-pound load up 1 foot in 1 second.

To illustrate the point that power is torque multiplied by time again, the horse lifting that load 1 foot is the torque hence the unit foot-pound (lb.-ft.) or Newton-Metre (NM). Adding a time scale i.e. 1 second turns it into horsepower (hp).

So, torque is the mother of horsepower.

We’ll leave out the calculations, but 1 mechanical horsepower (hp) equals 745.7 Watts, (0.7457 kW), or 1 kW equals 1.341 mechanical horsepower (hp).

An important note here: Horsepower figures are notoriously varied in different regions as there are different calculations to arrive at different figures. That means, the horsepower figure may be higher or lower. As such, the European Union issued Directive 80/181/EEC in January 2010 that kW must be used as the main unit while horsepower as supplementary. This is why manufacturers specify engine power in kW in all their brochures while leaving out hp.

So, how do torque and horsepower influence engine performance?

Let’s take two bikes of the same model and fit each with an engine of different torque and horsepower rating. Bike A has 150 Nm of torque and 100 hp. Bike B has 100 Nm and 150 hp.

Bike A would get off to a quick start but couldn’t hit a higher top speed. However, we could load up the bike with a passenger and lots of luggage since the high torque isn’t so affected by the weight. This engine is good for cruisers and tourers since they need to carry all that extra weight.

As for Bike B, it needed a little bit more time to reach speed, but it’ll take off at a certain point and hit a higher top speed than Bike A. However, loading it up with a passenger and lots of luggage will see it getting sluggish and struggle to get up to speed. This engine is suitable for sportbikes, so long as weight is kept as low as possible. It also means that the bike needs to be launched off the line at higher revs.

However, the above is the likely scenario on a straight road without traffic. In the real world, torque is more important as it gets the bike accelerating and rolling. Here, horsepower is only useful for us to reach certain speeds, say 110 km/h, 130 km/h 160 km/h and so forth. Yes, big horsepower figures will take us to much higher speeds, but it’s capped at 299 km/h anyway. Outright horsepower is truly useful only at the track, while torque is useful everywhere.

While it’s amazing to see higher and higher horsepower these days, do keep an eye out for how much torque the engine produces and at what RPM. Torque should ideally be produced at lower RPMs. The engine is considered “peaky” if torque is available too high up in the rev range, meaning we need to rev the engine like crazy or wait until the revs pick up for acceleration. This isn’t ideal – in fact irritating – in the real world. The reverse is true at the track where high engine RPMs are used all the time.

Hope that clears it up. Show your friends this article when you get into an argument about torque versus horsepower.

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