# What is the difference between horsepower and torque?

So I’m looking at the technical specs for my new car, a Hyundai XG350. It’s listed as:

Horsepower: 194@5500 rpm
Torque: 216@3500 rpm

I have a vague idea what these mean–generally more horsepower/torque means better acceleration from a stop, better acceleration when passing, and more towing/hauling capacity.

Which one matters most for what application?
What exactly is the difference?

Also, this engine is the same one as in the new Kia Sorento SUV (the engines for newer Kias are manufactured by Hyundai), but the specs listed for it in that vehicle are:

Horsepower 192 hp @ 5,500 rpm
Torque 217 lb.-ft. @ 3,000 rpm

Why would putting the same engine in a different vehicle change the horsepower/torque? Is it because the engine would be tuned differently for an SUV than for a mid-sized family sedan weighing 600-800lbs less? And why would they tune it so that the torque peaks at lower rpm’s in the SUV?

I’m not a car guy, so go easy on me with the technical stuff.

Quick answer is torque is a force, horsepower is work.

So what does this mean? Well, look at torque as a force TRYING to rotate something. Torque can exist even though this something is perfectly stationary. It’s only a force. Compare to you trying to loosen a stubborn bolt with a wrench. It’s not moving, but you are applying a force to the wrench, and this is torque.

Horsepower is a measure of work. As such it is the force (torque) measured over time. Going back to our stubborn bolt, you finally get it loose and start turning it. You still apply force (torque), but now the bolt turns and you are also performing “work”.

So this leads to a simple equation: Horsepower = Torque * rpm * constant

The constant is 1/5250, so the equation turns into:

Hp = torque*rpm/5250

You may wonder why the torque peaks at one rpm, and horsepower at a higher rpm? This is simply because torque reaches a peak at a specific rpm (in your case 3500 rpm) and then starts decreasing. But as the rpm is INCREASING, hp is still higher at 4000 than 3000, and higher at 5000 than 4000, all the way to 5500 where the torque starts dropping off so fast that the horsepower decreases.

Now what does torque and hp mean in the real world? Well, horsepower is what you sell a vehicle on, and torque is what the driver uses… Good torque will get a heavy vehicle moving from a stop. Good torque will make a low cruise rpm possible (with proper gearing) to increase economy and lower noise. Good torque will enable you to pass quickly. Yet horsepower makes for bragging rights. Kinda unfair.

A good engine has a wide torque curve (good torque all the way off idle to maybe 4000 rpm). That’s the rpm range most of us use. What the horsepower is at 5500 rpm is of rather academic interest.

Finally, why the different power ratings for the same engine in different vehicles? Without having studied these vehicles in detail I feel it is likely due to different exhaust systems.

/Markus

I didn’t ask the question, but that is a great answer, zwede.

Isn’t it correct that higher horsepower tends to equate to higher top speed? If so, I think you may have the reason why horsepower sells, silly as that may be.

The differences stated are quite small making it possible the inherent error in measurement is responsible.

Horsepower doesn’t necessarily equate to a higher top speed. The various gear ratios in the transmission and the final drive ratio of the differential are the determining factors. It’s likely, however, that an automobile with a higher horsepower rating will be geared to achieve a higher top speed.

Not to mention body weight, drag coefficient, friction, exhaust and other losses…

Probably because they’re assuming the SUV owners will be hauling trailers or doing other work that requires more torque but at a lower RPM.
However, I’m with UncleBeer on this one, we’re talking 2 hp and 1 lb-ft of torque, the differences will be negligible.

Also,

The difference in the two from one vehicle to the next may depend on the drivetrain that is connected to the engine. The horsepower and torque ratings, I believe, are rated as the output at the wheel, not the crankshaft. So depending on what transmission and or transfer case plus the differential are installed in the vehicle you will get different ratings. Since an SUV will have a different setup than a passenger car you will have different losses through the drivetrain equating in slightly different numbers.
An SUV may have the same engine but they may install a different camshaft in it to give it a different torque curve verses a passenger car.
Finally, the SUV may have a slightly different air intake, a different computer chip, and a different exhaust than the passenger car.
You can expect to loose ABOUT a quarter of the horsepower/torque through the drivetrain.

No, that’s generally not the case. Most HP numbers you see printed are BHP where the B stands for “brake” (engine brake) which is a device they mount the engine to to measure power output (suprisingly enough ) So they are being measured at the engine crankshaft, without all the drivetrain attached.

Check out Anthracite’s Primer on the Subject

Thanks everyone, especially zwede.

No, because the transmission’s job is to provide different torque ranges. A car’s HP and torque specs are measured with the engine bolted to a dyno (basically a giant water pump).

That’s why you can’t take off from a dead stop in 4th gear. It takes an incredible amount of torque. Way more than your engine can generate.

The difference between torque & HP is also why big diesel engines always have much lower HP ratings than smaller gasoline engines. Because they generate much, much higher torque.

Excellent post Zwede

Could you guys give a cite about the advertised horsepower measured at the crank and not the drive wheel. It`s not that I don`t believe YOU guys. When I discussed this topic with a gearhead buddy of mine he stated that he was sure that advertised horsepower these days was drive wheel HP. He noted that in the muscle car era all the HP numbers where inflated because they used misleading and inflating crank HP numbers. I guess they supposedly advertise the true HP numbers these days by giving the practical drive wheel HP.

Who`s right?

Do you mean that diesel engines have a wider torque band? If it’s just higher torque, you can use a higher gear ratio and extract the same horsepower.

take a look at this.

>>>>>Could you guys give a cite about the advertised horsepower measured at the crank and not the drive wheel. It`s not that I don`t believe YOU guys. When I discussed this topic with a gearhead buddy of mine he stated that he was sure that advertised horsepower these days was drive wheel HP. He noted that in the muscle car era all the HP numbers where inflated because they used misleading and inflating crank HP numbers. I guess they supposedly advertise the true HP numbers these days by giving the practical drive wheel HP.<<<<<<

No citation is necessary. if the advertisement lists brake hp, that’s what it is. Otherwise these days we just assume it’s net horsepower.

The difference in horsepower figures from the muscle car era and today is the fact that earlier ratings were of gross horsepower produced by the engine without power draining accessories. Now manufacturers typically rate the engine running with all it’s accesories, listed as net horsepower. Net horsepower is always less due to the frictional drag of the accessories.

Wheel horsepower, lower still, is measured on a dynamometer and incorporates losses due to the drivetrain.

Net horsepower is used because it is a more accurate rating of the engine as the customer buys and uses it compared to gross horsepower.

It is also much easier for a manufacturer to rate the engine once in each configuration (engine, intake exhaust, accesories) used in a model line than to rate it separately with different transmissions, gear and/or differential ratios, body styles, wheel tire combinations.

To illustrate this point, imagine if Chevy had to test and rate separately every possible permutation of it’s Silverado pickup truck using each engine. There are literally hundreds of combinations. To simplify things, every Silverado with the same 5300 (combination) is rated at 285hp. This would not be the case if Chevy were listing rear wheel horsepower.

I have noticed that there is a lot of contradictory information on the web vis a vis this topic.

Take for example this Edmunds.com editor, Karl Bauer, who even contradicts himself:
http://www.edmunds.com/editorial/techcenter/horsepowernetvswheeldriven/43845/

http://www.edmunds.com/ownership/techcenter/articles/43845/article.html

Can someone clarify -

What the OP adressed was horsepower (194 to be exact).
Is this BHP or the same as BHP or considered to be BHP?
Or is this Net, Gross, Actual, Road or Wheel HP? Now I`m really confused.

So far

Stan - HP in the OP is net (with accessories, minus drivetrain)

RACEKARL, Hail Ants - HP in the OP is gross (engine only, not sure about accessories, no drivetrain)

Fuckwhistle - HP in the OP is (road or wheel, includes everything)

Who wins? My money is on Stan, but I would only bet a nickle.

The horsepower and torque information in the OP is copied directly from the company website, and they offer no info about what method is used to determine hp that I could find.

Advertised horsepower and torque is always measured at the engine, never at the wheels.

“BHP” (brake horsepower) is an old way of saying “horsepower”, not really used that much anymore. The terms are interchangeable.

As per a previous poster power used to be measured according to the SAE gross standard which allowed the engine to be measured with any exhaust system, no accessories (not even a waterpump), etc. This was at the engine. In 1971 the new SAE NET standard was introduced, with most 1971 vehicles rated according to both standards. SAE net was engine power, like Gross, but specified that the production exhaust system be used, as well as all accessories. It also specified a more realistic intake air temperature. For instance I happen to own a 1971 vehicle which was rated at 365 hp SAE Gross, and 285 SAE Net, so you can see there was a big difference. By 1972 everyone was only rating according to SAE Net.

To make things slightly MORE complicated, the SAE standard is a US standard. In Europe cars are measured to the DIN standard (Deutsche Industrie Norm). Basically the same as SAE Net, but specifies a slightly higher intake air temperature and humidity which makes the power a little bit lower (approx 1-3%).

The Japanese have yet another standard. I forget the acronym, starts with a “J”. This one gives slightly HIGHER results than DIN and SAE.

And finally, if anyone is wondering how much power a typical car actually puts to the ground, I took my Camaro to the dyno a few years back. It was rated at 285 hp SAE Net, and put 243 hp to the ground. Older cars usually have higher losses, and automatics have higher losses than manuals. Some older automatic cars can have losses in the 25% range. Some newer manuals only 15%, or even less. Front wheel drive typically has lower losses than RWD, and AWD have the highest losses.

/Markus

AFAIK Stan Doubt is right. Its listed as NET HP. All accessories (fan,alternator,power steering,etc) and no drivetrain (for the reasons Stan Doubt mentioned).

Not to nit pick (always said right before a nit pick) but, av8rmike you are right about all the things you mentioned limiting top speed EXCEPT weight. It will take you longer to get to your to speed because of extra weight, but its not going to slow you down any. It may actually make you have a higher top speed because the car is lower to the ground. This was all discussed here a year or so ago.