Horsepower and Torque

We’re thinking about getting a second car – Yay!

We’ve been looking rather longingly at the Mazda3 5-door. But when I look at the numbers, I get a little… confused.

Mazda 3 (2008 5-door)
Outlander (2003 AWD)
2983 lbs 3461 lbs
4.8 inches ground clearance 8.3 inches ground clearance
Fully independent 4-wheel suspension Fully independent 4-wheel suspension
2.3 liter engine 2.4 liter engine
156 hp @ 6500 RPM 142 hp @ 5000 RPM
150 ft/lb torque @ 4500 RPM 157 ft/lb torque @ 2500 RPM

Take a look for a moment at those numbers. Notice anything… odd? The Mazda has a slightly smaller engine… yet it develops more peak horsepower! How can this be?

And look at those torque numbers… the Outlander develops more torque at lower RPMs. Unfortunately I wasn’t able to find a graph of horsepower and torque curves, so we can’t compare them like that, but still, it makes you wonder.

We’ve taken the Mazda3 for a test drive – it’s definately a spunky little car with lots of “get up and go.” Moreso, I dare say, than my beloved Outlander. And yet… those torque numbers continue to befuddle me.

Horsepower vs. Torque

Horsepower and torque are confusing ideas – we all tend to think we understand them, but when you look at their definitions, you can’t help but feel a little confused. We often tend to think of more horsepower as good, because it makes the car faster, right? Well, horsepower is “work done over time.” Now try to work out in your head how being able to do “more work done over time” makes your car faster.

Same thing for torque – which few people even pay attention to. Torque is just rotational force – which gets really confusing when you realize that even if something is not rotating, it can still have torque! For example, when you try to turn a stuck bolt, you’re applying torque – even if the bolt isn’t turning.

Given that, you’d think that torque would be a very important number for cars – more turning force seems to imply that you could turn the wheels faster, right? Well, yes and no. You see, it’s not just raw turning force – you’ve got to consider that your car produces different amounts of torque at different engine speeds (RPM), and then you’ve got the gear ratio to consider (different for each gear your in, plus the gear ratio of your drive train). If you’re a casual car buyer, trying to figure all this out can give you a major migraine.

There’s got to be an easier, more objective way to measure things, right?

Power to Weight Ratios

Looking back on the Outlander vs. Mazda3 chart, I realized that it may just be the weight numbers that are throwing off my perceptions – the Outlander is quite a bit heavier, due in no small part to it’s (fantastic) all-wheel-drive system. So how can we compare?

A little bit of digging on the subject turns up the term “power to weight ratio.” Ahhhh, here’s what we’re looking for!

Mazda 3 Outlander
Torque/weight ratio 0.050 0.045
HP/weight ratio 0.052 0.041

Ah, now that’s a bit better. We’re still ignoring the final drive ratio (produced by the drive train, etc.), but this is much better for comparing power “at a glance.” And now we can see why the Mazda3 feels “zippier” – it’s power/weight ratio is a bit higher than the Outlander’s.

Of course, this reveals another anomaly – the Mazda’s HP/weight ratio is higher than it’s torque/weight ratio, while with the Outlander the opposite is true. But it’s not really much of an anomaly if you look at the rated towing capacity of the two cars – the Outlander is rated to pull (much) more than the Mazda.

So there you have it – the means to (somewhat) objectively compare horsepower and torque ratings between cars, so as to get a sense for their performance. It’s not the total picture, and of course you should still drive a car before you buy it, but perhaps this will help you narrow down your choices (as it sort of did with me).

Author: Keith Survell

A geek, programmer, amateur photographer, anime fan and crazy rabbit person.

9 thoughts on “Horsepower and Torque

  1. could you please explain me if
    150 torque at 4000 rpm
    and 150 torque at 2000 rpm
    and 150 torque at 6000 rpm
    which of these is a powerfull engine

  2. and this one also
    if the power is 150 hp at 4000 rpm
    and 150 hp at 2000 rpm
    and 150 hp at 6000 rpm
    which of these is a powerful engine
    sorry to bother but i wanted a simplified answer so i framed my question so
    thank you very much ,I `d appreciate if you`d take some time to answer these 2 questions

  3. I’m sorry, your questions don’t make any sense – what you have described are all equally powerful engines. The only difference is the engine speed (RPM) at which they develop that power.

    The engine that develops its power at 2000 RPM will be very quick off the line – a good city car, I’d imagine. It will respond quickly to changes in throttle input. But when you’re on the highway, or any other situation where you’re forced to rev the engine quite high, the power will drop off and it won’t be as responsive.

    Likewise, at the other end of the spectrum, the engine that develops its peak power at 6000 RPM will not be as responsive “off the line” or at low throttle positions. However, as you continue to push the throttle (gas pedal) down, the power will continue to build as the engine’s speed (RPM) builds.

    All these hypothetical cars you’ve asked about are all the same in terms of “power.” No one is more “powerful” than the other.

    Think of it like two runners in a race – one runs really fast at the beginning of the race, but gets tired (and slows down) at the end. The other runs rather slowly at first, but then does a burst of speed at the end. Both runners finish the race at the same time – the only difference between them is how they got there.

    Also, trying to decide which engine is more “powerful” is a useless comparison unless everything else is equal – as I said in my article; you should consider looking at the power/weight ratio instead for a better comparison statistic.

  4. So if you want a car that is good at towing things, would you want a car/suv/truck/et.al. with high torque at low RPMs to aid in getting whatever you’re hauling moving and peak hp at higher RPMs?

  5. This page wasnt working this morning. i tried visiting it but it timed out 4-5 times now but i can access it now. Why did this happen? Am i the only one having this error?

    1. I’m not sure why you were having that problem. My guess is something between you and the server on which this blog is hosted.

      My monitoring tools detected no downtime, and the 3rd party service I use to monitor the status of this site reported no problems either, so as far as I can tell, the site was up & running all day.

      It happens sometimes, even to the best sites, and there’s not much you can do about it – the Internet is vast and complicated, and although incredibly robust, sometimes it doesn’t work quite right (at least for a little while). Sorry!

  6. I always like to see who is fastest in a 0-60 mph test. This says more than anything else for most people.

    1. 0-60 times are a good comparison that everyone can easily understand, that’s true. (As long as you remember that they are basically just measuring straight-line acceleration.)

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