Going over Nissan’s specifications for the 2011 Quest minivan, I came across these for the engine, on both the media and the consumer site:
260 horsepower @ 5,200 rpm
240 foot-pounds @ 4,800 rpm
Some non-Nissan sites provide slightly different numbers:
253 horsepower @ 5,200 rpm
236 foot-pounds @ 4,800 rpm
So perhaps Nissan recently found a couple more horsepower then rounded both figures up to the nearest five.
Both sets of numbers instantly struck me as impossible.
Torque is the amount of force exerted on the crankshaft at a given moment. Horsepower is torque multipled by rpm and then divided by an arbitrary number, 5252 in the case of SAE BHP and foot-pounds. Given this, at 5,200 rpm an engine must be producing a bit more foot-pounds than it does horsepower, specifically 262 in the first case, while the Nissan specs require that it be producing less than 240.
Why less than 240, and not 240? Because the torque curve cannot be flat all the way from the torque peak to the horsepower peak. At a certain point, an engine produces less and less torque as rpm increase. This is the torque peak. For a while after this point, rpm continue to increase faster than the torque falls off, so horsepower continues to increase. When torque output falls more than rpm increase, you’ve got the horsepower peak.
Most likely: the power peak is actually around 6,000 rpm, as with the similar V6 in the Murano. But why hasn’t anyone at Nissan or any of the initial reviewers realized this?
Michael Karesh owns and operates TrueDelta, an online source of automotive pricing and reliability data
At some point, they will be sued, just like the lawnmower manufacturers were, and we will all be getting a check for $2.45. The lawyers of course, will make millions.
Way to go Nissan, I thought a new Honda Odyssey and a first gen Kia Sedona had a love child, upon my first glance at that van. (Shhhhhhh don’t tell their parents they’d never approve.)
I know I live in a glass house — I drive a Chevy Astro — but that van looks horrific.
I was going to say the same thing.
Makes my ’05 Saturn Relay weather beater look downright attractive.
I guess I’ll come across as strange when I say this, but I think it’s the best-looking minivan ever made. If I needed one, I would buy this one.
Perhaps they wanted to accentuate the numbers from a useful RPM range.
Would I be thrown out of the TTAC club for admitting that I have no idea exactly how the torque/horsepower numbers work? For instance I was looking at the t/h numbers for the current generation Accord 4-cyl (sedan – non-EX) v. previous generation Accord 4-cyl and it looks like the extra power comes in at much higher RPM which led me to believe that the engine had the same power, but they are choosing different RPM figures to express their power output. (I’m hoping I didn’t completely lose the people who know more about this than I do.)
It’s easier to understand with a graph. GM and Honda are good about posting those online; other manufacturers not so much.
Would I be thrown out of the TTAC club for admitting that I have no idea exactly how the torque/horsepower numbers work?
Nah… I only understand because of a steady diet of “Hot Rod Magazine” from when I could read till I moved out of my parents house after graduating college. And I was a Four Wheel and Offroad subscriber which is the only reason I understand the basics of diesels so well.
tankinbeans,
Extra power is extra power, so the new Accord does have more of it.
A rough way of looking at it is that torque is almost level across the rev range except at either end, and power is basically torque * rpm. So it’s possible to increase power by moving redline up higher but keeping torque output constant. Or you could increase torque throughout the rev range, which would increase power at every rpm level. The new Accord’s engine is physically different from the old one (K-series vs. F-series) and it’s just better everywhere [in the rev range].
@tankinbeans
Don’t feel bad, I still haven’t had time to figure out SAE J1349 Certified Power yet. And it’s been, what, going on 7 years now or something…?
http://www.sae.org/certifiedpower/brochure.pdf
@Carlisimo
I didn’t realize the two engines were different. I guess I assumed that since they’re both 2.4 liters they would end up being the same, but with a few minor tweaks.
Many automaker website specs are riddled with errors. Mazda USA’s website insists that Mazda6 has “MacPherson strut front suspension” even though the car is equipped with an upper A arm in front, just like its sister car Ford Fusion.
I’m painfully aware of this, since I must gather information from various sites to provide TrueDelta’s feature and price comparisons.
I still haven’t gotten up the motivation to tackle this year’s Chryslers–they’re always the worst.
This was a rare case where the error is obvious because the specs are mathematically impossible.
These days, variable valve events, variable intake manifolds, and electronic boost controllers on turbos can do some weird things to the shape of the torque curve. That doesn’t alter the basic mathematical premises, but multiple torque maxima can produce the sort of results you cite.
Actually, multiple torque maxima CANNOT produce the Quest’s specs, because as you also say technology cannot alter the formulas.
I’m guessing it’s a typo and most auto reviews are just too lazy to notice.
Probably should read 260hp@6200 or something. The 2011 Quest’s tach puts a redline at 6500.
I’d just call up Nissan and ask.
Maybe they were tweaking engine specs to make certain emissions or fuel economy ratings. Are the media and consumer press release dates vastly different from each other?
So how come Americans get this… thing and the Japanese get this bad looking MoFo.
http://www2.nissan.co.jp/ELGRAND/e521008g01.html?model=ELGRAND&gradeID=G0
The get a cooler name too. Elgrand Highway Star. Pardon me while I go crank Deep Purple up to eleven…
now THAT’S hideous
Quick physics lesson- torque is the twisting force on the crankshaft. A 200 pound weight hanging from a 1 foot lever would be 200 ft lbs of torque. A 100 pound weight hanging from a 2 foot lever would be the same.
Many people say torque is what you really “feel”, and that’s true to a certain extent. What you feel is force at the tire’s contact patch, which is your crankshaft torque multiplied by all your gearing. If you have 200 ft lbs of torque, and a 5:1 overall gear ratio (right down the the radius of the tires), you’ll have 1000 pounds of force accelerating your car. Double your tire size, or halve the mechanical advantage of your gearing by shfiting, and you have 500 pounds of force. However, what kind of gearing is practical to spec is determined by horsepower. That essentially tells you how high you can keep revving while still making decent torque. Being able to rev higher means you can hold a lower gear for much longer.
Here’s an example: Take an engine that makes 400 ft lbs of torque at a 4500 rpm redline, and another that makes 200 ft lbs at 9000 rpm. They both make the same peak power. If all else is equal (weight, shape of torque curve), we just put twice as low of gears in the little engine and we get the same acceleration.
Or, take the BMW 3-series. The 335d makes 420 ft lbs of torque, and the 335i makes 300 ft lbs. However, the -d has a higher rear-end ratio. They just happen to have exactly the same gear ratios in the transmission. In first gear, they generate about the same force at the rear wheels (the -d makes about 7.5% more). However, the 335i can hold onto first gear for 40% longer than the -d. When the d is almost half way through 2nd gear, the i is still in first, and is able to generate far more torque at the rear wheels than the -d. Therefore, horsepower is a pretty good way to compare the performance of the two cars, and acceleration numbers bear this out.
However, high-revving cars often tend to not make much low-end torque, and therefore not much low-end power. This means a downshift is often necessary to get decent acceleration. With a high torque-car, you just open the throttle and you’re instantly making more torque, and thus power, without having to shift. This makes torquey engines nice to drive day-to-day.
Some people oversell this though and say “torque is what really matters” or even “…all that matters”. Lets take an extreme example to demonstrate why this isn’t the case. I can generate a peak of about 100 ft pounds of torque on my bike. That’s competitive to some econo-cars, or a harley davidson. However, I can only generate that much up to about 80 rpm or so, and the car or motorcycle can generate that up to about 6000 rpm. Could you imagine pedaling a Versa or Harley? Lets take an extreme example- a five foot breaker bar in place of the engine. I could easily generate four or five hundred pound feet of torque with this, but only at maybe 8 or 9 rpm. That’s no replacment for a Vette or Viper engine, although I’m sure I’d have good acceleration from 0 to 1/64th mph :)
By the way- 260 hp at 5200 rpm means the engine must be making 263 pound feet of torque at that rpm. Quite a feat when the peak torque is only 240 ft lbs.
@carve
Thats a great explanation! I always wondered why my early 60’s VW beetle with 40 HP was so (relatively) fast out of the hole… til about 10 MPH when I had to shift to second, and it bogged. I tried one of the BMW diesels, and it was great, but the idea of looking for cow pi$$ when it runs out of urea just doesn’t appeal to me. That, and I think diesel prices are going to spike.Thanks again for taking the time to type all of that out.
I agree with what BMW said. Thank you for the explanation. Now please excuse me while I douse my head in water to alleviate that smoking coming from my brain. ;)
I think I understand what you said, but the melting of neurons has commenced.
You know you’re on a real car-guy site when the first user comment trying to explain torque vs horsepower gets it exactly right.
Good stuff. The very last sentence was of course my point.
Thanks. I had some edits, but was too late. Here’s an addendum.
Force and torque are pretty self explanitory.
Work is force times distance. It’s actually using that force to do something, like lift a weight or accelerate a car.
Power is work / time. It’s how quick your engine can do a given amount of work.
So, torque is pretty much the force your engine generates, but horsepower is how quickly the engine can actually get something done.
If you go back to my example of a 200 pound weight hanging from a one foot bar, you have 200 ft lbs at 0 rpm. You can’t do any work with that- it makes 0 horsepower.
So, horsepower ultimately describes what an engine is capable of, and that’s why it’s in all the adds. Torque gives you an idea of how it gets done. For a race car engine that spends all it’s time on-boost, near redline, horsepower is really all you need to worry about. For a road-car, you want a balance between low-end torque and the ability to rev.
Since road cars spend their lives across the rpm range, what really matters is the total area under the torque curve. It’d be nice if such a number were published.
“Since road cars spend their lives across the rpm range, what really matters is the total area under the torque curve. It’d be nice if such a number were published”
A long time ago I sat down with a bunch of friends and wasted an enormous amount of time trying to figure out how to usefully quantify the area under the curve. But rather amusingly, one friend is a motorcycle racer, another one was from the Uncle Ben’s Too Fast Too Furious club, and I’m in the shove-me-around-Sebring-with-displacement club. So right off the bat we couldn’t agree where the numbers mattered most, or how to weight the numbers, or really how to do anything more than drink through my beer supply.
Short of simply looking at the curve and drawing conclusions, I’m not sure it would be possible to usefully convey area under the curve.
Plus, looking at a curve — if you are also fortunate enough to have the smoothing disclosed — can show you a lot of really useful stuff like weird dips or the severity of fall-off after peak and other factors that aren’t easily converted to a nice bite-sized number.
But Peak HP and Peak TQ numbers are almost always far more useless than the supposedly oversized pickup trucks TTAC has decided to start hand-wringing about.
The area under the curve can be objectively measured, if you’re willing to concede that every engine speed should be equally weighted. Which, perhaps, many people are not.
Yes- it could be objectively measured and displayed as “foot pound revolutions per minute”. Kind of a mouthful, but I think such a rating would be more kind to your typical car engine than to racier engines, like the WRX. That thing is a slug below 4500 rpm. Most people, for an every day car, don’t want something they have to rev the piss out of to get any performance from. However, most people also expect more power when they rev it up, and a diesel or a glorified tractor engine will also disappoint.
Foot pound revolutions per minute is really just another way of saying “power”, but in this case it would illustrate something more like average power rather than peak.
When I wrote a rebuttal to the NYT editorial here, several posted I should get a column. I’m going to return the favor. Carve should get a column – GREAT post and additionally discussion.
A while back I built an Excel file to compare thrust:weight at the pavement. It doesn’t take the shape of the torque curve into effect, or converter slip for automatics, or electronic neuters and so would not be generally accurate with differingly peaky entries or GM cars.
The example given shows two cars (3.7 Mustang, 5.7 Challenger) with very different paper powertrain specifications yet similar timed performance within a few tenths. But as the calculation shows, where the rubber meets the road they aren’t very different at all.
http://preview.tinyurl.com/2uramc8
Carve – thank you. I now have this to copy and paste (no worries, I’ll credit you for the work) when I get into a power or torque argument with someone when talking about sports cars.
Excellent explanation, Carve! All angles laid out clearly and concisely.
I’m really not surprised that Michael Karesh was the only person who noticed that Nissan was disseminating impossible specs. I was at an S2000 club tech day recently, and the tuner presenting his product had an A HA! moment when I explained to him the formula for deriving horesepower from torque and he realized that they were always equal at 5,252 RPM on his dyno graphs.
I don’t suppose a torque limiter could be the culprit? If the torque curve was flat to 5500 RPM, you could easily see the horsepower number they’ve given. In this case, they’d just be quoting the beginning of the range.
No. If the engine made 240 ft/lbs at 5,200 rpm, then the hp at 5,200 rpm would be 237.6. Extending a torque plateau above 5,200 rpm wouldn’t elevate the hp at 5,200 rpm, but it would elevate the engine speed at which the hp peak is achieved.
Incidentally the 5252 number is not arbitrary, it is 5252.113… . and it is exactly 33000 divided by 2 pi. The 33000 comes from the definition of a horsepower, 33000 ft lb per minute.
So hp=torque in ft lb*rpm*2*pi(to convert from revs to radians)/33000
Fancy not knowing that properly. That was high school science, thirty years ago.
And the 33,000 is arbitrary. Somebody at some point decided that that number roughly approximated the output of a horse. But it could have just as easily been 32,000 or 34,000.
Something in the recesses of my memory is saying the 33000 came from dividing what 3 (standard bred?) horses could pull by 3. Arbitrary mind be a bit of a harse word to use … although oddly enough fitting in light of the deceptive publishing tactics used on blurry-eyed readers.
Yes Michael, at some point somebody (Mr Watt) decided that he wanted to use a particular and arbitrary number for the definition of a horsepower. My point is that 5252 is regarded as some sort of magic number on the interwebs, whereas it has a good solid explanation, based on a 200 year old definition. Your article continues the magic number meme.
So, the question is: Is there anybody responsible for making manufacturer’s numbers accurate, do they have any teeth at all at enforcing any violations? Or can the manufacturers said anything they want?
The first post mentioned manufacturers getting sued for inaccurate numbers. By whom? Class-action lawyers on behalf (ha!) of consumers? Attorney generals? Seems like the chance of this is pretty low, given how apparently prevalent these inaccuracies were.
Thanks to Carve for the explanation, BTW. Better than any I’ve read on the subject. The quality of the commenters here on this site is amazing, not discounting the writers, of course!
The Society of Automotive Engineers (SAE) has published standards for horsepower ratings. I think SAE J1349 is the “net” power rating, but there’s another standard for “certified” power ratings that involve ISO-compliant testing facilities and observation of testing by third-party observers. I think the only real teeth to these standards, like most US standards, are car owners’ ability to sue manufacturers for false advertisement should they opt to not comply with the standards and get caught.
Thanks also Greg Locock; I was scrolling down to see if someone pointed out that 5252 is not a random number. Unit conversion constants are never random.
Random and arbitrary are not the same thing. Random numbers shift about, arbitrary numbers stay the same once they are specified. See my response above.
I’m wondering why a vehicle as heavy as the pictured minivan (which must weigh over 5,000 lbs) isn’t equipped to deliver torque at low RPMs. Seriously, I’m shuffling kids to school and soccer and grocery getting in my minivan. Most of the time I’m accelerating to and driving at less than 45 mph. I want the torque down low and I don’t really need it up high. What gives?
When multi-speed automatic transmissions are calibrated to downshift 1-2 gears when your foot casts a shadow on the accelerator your engine will be running up high where it produces torque. If the engine had low-end torque you would never utilize it because autos don’t let you lug your engine effectively. I recently upgraded from a 2000 Odyssey with the 4spd to a 2006 Odyssey with the 5spd and found I have to drive faster than 45 to get decent mileage or it won’t stay in 5th. Right at 45 it won’t drop into 5th or if you speed up to get it in it’ll kick out at the drop of a hat if you slow back down, so sticking at 48+ is more efficient than driving at 40-45.
@findude
I suppose a minivan is a multi-purpose vehicle so it is always going to be a compromise between all performance factors.
I guess a question to you might be “Just exactly how much acceleration do you need when hauling a van full of kids? 0-45 in 1.5 secs, burning rubber at every green light?”
Seriously, if that is what you want you DON’T want a minivan. Oh, and you probably shouldn’t be ferrying kids around.
(Just joshing with ya. I’m sure you are very responsible guy.)
What’s wrong with doing burnouts while transporting kids? It’ll make them happy! :)
Real men refer to “foot-pounds” while politically correct modern-day cubical dwelling metrosexuals use the term “pound-feet.”
That’s all I got to say about that.
No cubical here. I work from my dining room table!
I always remember the “correct” order because the metric is “newton meters” and someone at some time wrote an article stating that, given the definition of torque, the force should come first, the distance second.