A good example is my 9 year old CR-V. It has an advertised 146 HP and I feel confident that it has it all but the driver has to run the engine right up the red line to get it. Max Torque is close to the highway engine speeds but the torque feels low compared to alot of other cars I’ve driven. That said we’ve been quite satisfied with it for 162K miles now though a sixth gear for it’s five speed manual tranny would have been welcome. Use that sixth gear to drop the rpms another 350-450 rpm. Leave the other gears where they are now.

I numbers I am interested in are:

rpm of max hp
rpm of max torque
hp per lb
vehicle weight (to which I’d add the weight of our family, a full tank of gasoline, and a full load of luggage).

# Dynamic88 : The Model A perspective -

Recently a friend gave me a ride around town in his Ford Model A – 1931 Vintage. He said the engine made 37 horsepower. Most published figures I’ve seen rate it at 40. I’m not going to quibble. What impressed me is that for the most part, the A is quite capable of keeping up with city traffic. Sure, starting off from a stop is a bit slow – you can’t shift real fast, you need to hesitate a bit or it’ll grind. But as far as HP goes, 40 is all that is needed for city driving.

Yeah I like Model-As. I want to own one someday.

My ideal target HP to weight is around 100HP with a 2300 lb vehicle and five or six manually selected gears. If I could do it with a 1.4L then I’d be satisfied. Instead of making each generation of vehicle heavier, make each generation the same power and with the same weight and let the fuel mileage increase through tech advancement.

Following your example then, if the V6 were tuned to deliver peak torque of 220 ft-lbs at 4,295 RPM with similar curve characteristics (using multi-ports and variable valve lift) as the Turbo Four, they would perform about the same on the drag strip correct?

You are exactly right (and it’s funny that I just used the Ford 4.0L engine as a point of comparison). The Ranger/Explorer 4.0L V6 was tuned for strong low-end torque — its torque peak was only 2,400 rpm — but it was all done above about 4,500 rpm. There (probably) wasn’t anything wrong with it, it was just designed that way.

Why? To a large extent, all of the things that benefit power at low speeds will restrict it at higher speeds, and vice versa. Blame it on Bernoulli’s Principle. An engine set up for high-rpm power (with short intake runners, big valves, high valve lift and long duration) will tend to hurt low-rpm grunt because all of those elements reduce intake velocity at lower speeds. An engine set up to produce high intake velocities at low speeds (long, narrow intake runners, small valves, low lift, short duration) is too restrictive at higher speeds — at high rpm, the engine can’t get enough air.

Modern engines can cheat to some extent with variable valve timing, variable intake runners, and other tricks, but any engine design is still basically a compromise — it works best in one particular speed range, not as well at others.

Horsepower is a function of torque and rpm. It’s roughly torque * rpm / 5,252 (which means that power and torque are equal at around 5,250 rpm).

Let’s compare two hypothetical engines: a high-revving, DOHC 1.8 L turbocharged four (something like the engine in many VW and Audi products) and a slow-revving, OHV, 4.0 L V6 (something like the engine in older Ford Rangers). Let’s say the four has 180 hp @ 6,000 rpm and 170 lb-ft of torque @ 4,500 rpm, and the V6 has 160 hp @ 4,000 rpm and 220 lb-ft of torque @ 2,400 rpm. Let’s also assume that the turbo four, like many modern turbos, has been tuned to provide most of its torque through a broad rpm range (say, 1,800 to 5,500).

Trundling along around town, turning 2,400 rpm in fourth gear, what do we find? Let’s say the turbo four is producing 95% of its peak torque at this speed, 166 lb-ft. The V6 is at its torque peak at this speed, 220 lb-ft. At this speed, then, the V6 is making about 100 horsepower. The four is producing only about 76 horsepower.

The V6 makes more horsepower up through 4,000 rpm (its power peak). At that speed, its torque has started to drop off a little, but it’s still about 210 lb-ft, and it’s making 160 hp. The turbo four is still making about 166 lb-ft of torque at this speed (thanks to that flat torque curve), and around 126 horsepower.

Now, here’s the trick. Above 4,000 rpm, all of the design elements that give the V6 its strong torque at lower speeds start to work against it (this is mostly a matter of air flow). Its torque starts to drop off rapidly (if it didn’t, its peak horsepower would be higher). The turbo four’s torque is starting to drop off, too, but not as much, and raising its rpm still adds more power than the diminishing torque subtracts. At 6,000 rpm, the four is still making 158 lb-ft of torque, and its peak horsepower, 180 hp. Assuming the V6 can even rev to 6,000 rpm (and it might not be able to), it’s now making less torque and less power than the four. (Even if it’s still producing its peak 160 hp at this speed — unlikely — its torque would have dropped to about 140 lb-ft!)

What does this mean in the real world? If you installed these two engines in otherwise identical vehicles with the same gearing, tires, and overall weight and put them on a drag strip, the V6 would take the four off the line, and stay out in front until a moderate speed — maybe 35-40 mph, depending on the gearing — because at low speeds it has more power. Above that speed, the turbo four would start to pull ahead, and it would win the race with a noticeably higher trap speed.

The peak value for torque, as you may have gathered, is not that useful unless you also have a sense of the engine’s torque curve — how much torque it puts out at different engine speeds. Ideally, you want an engine that produces most of its maximum torque at all engine speeds (a very flat torque curve), but with internal combustion engines, you can only approximate that.

Apparently, the torque curve for that engine peaked out at a low RPM and then dropped off abruptly (unless I had a maintenance problem with that vehicle). It was rated at 155 BHP (CA version) and I forgot the max rated torque and associated RPM.

One of our work vehicles is a Chevy Suburban that we carry medical equipment around in to get to the airport and hospital, etc. That vehicle, as opposed to the Explorer, seems to have a broad torque curve (power band) as it pulls strongly all the way up from idle to redline.

Perhaps we never even “feel” HP at all. We’re just feeling the torque curve/power band all along and use “Horsepower” as a term because we can relate to it as something tangible in our mind (horses) rather than something arbritrary like “foot-pounds”.

Anyone else know?

I understand the mathematical relation of the two but can someone explain the difference of HP and Torque when it comes to the driving experience?

All I know is a low-end torque motor gives great accleration, pull loads, climbs hills. What does HP do exactly?

If the automakers are selling a small car, then they’ll generally advertise the maximum HP from that curve. If they’re pushing a musclecar, it may not necessarily be in their best interests to publish max HP; rather they may list an accurate HP rating taken from their derived curve at a lower than maximum number at a lower RPM. It’s still accurate from the curve, just not maximum. But then no regulating authority has ever stated that HP ratings have to be advertised as maximum, just accurate. This was sometimes done with late 60s – early 70s musclecars to keep insurance rates lower and therefore avoid scaring away potential customers.

And yes, as an earlier post described, prior to 1972, Gross BHP was the standard. This was when an automaker tested their engines with no accessories, open exhaust, open air intake, and tuned to optimum performance. From 1972 to the present, Net BHP is the standard, as engines are tested with full operating accessories, stock exhaust w/ cats and mufflers and stock air cleaner with filter and cold air hoses. Before and after 1972, engine brake measurements are taken at the flywheel.

All measurements are corrected to standard atmospheric conditions to a barometric pressure setting of 29.92 inches of mercury and 15 degrees Celsius. In the real world, especially on a hot day and a higher elevation, the density altitude will be higher than actual (pilot terminology) and a normally aspirated engine will generate less power than “normal”. On a cold day at sea level (colder than 15 degrees C) and a high barometric pressure (say 30.52″), the same engine will produce more HP than “normal” (at WOT and a high RPM).

I agree that drive wheel HP ratings are the most accurate and reflect real world conditions. As long as every automaker followed the same standards in measuring power, then it would certainly make things easier on the consumer. But because European and Asian companies are allowed to do things their own way…

Try as everyone might to slam GM. This speaks of integrity.

Here is a case where GM told Nissan to ,”Grab the Pebble from my Hand, Grasshopper.”

And they showed up with a doctored pebble.

The U.S. has strict guidlelines that the Big 2.8 have to go by. The Imports don’t.

In fact, the car was just as fast when I thought it had 181 hp as it was when it was determined that US/Canadian de-tuned for emissions cars had 170 hp.

The 2002 Sonata was so much better overall than Detroit junque, I decided to go for a 2007 Sonata and it’s been a far better car than virtually any others we’ve ever owned. As have our Prius’s.

If the underrating wasn’t already known on every car forum, then you’d basically have the equivalent of a “sleeper” where you’re really pushing 50H more than everyone thinks.

If I spent the money on a Mustang Cobra a few years ago, and discovered that it was down by 30 HP because of casting flash inside the intake manifold, I’d be pissed. On the flip side, if I discovered later that it was actually UNDER-rated by 50HP, then I’d be happy as heck because now my car has that “sleeper” advantage.

Thats all well and good for performance enthusiasts like yourself and myself. However, 90% of the market doesn’t give a rats ass about WHP, BHP, drivetrain loss, etc. All they know is what the marketing gurus put in the adds. Put this way, my girlfriend doesn’t know crap about cars. All she knows is she likes Ferraris more than Lambos, BMWs more than MB, GM more than Ford, and Nissan more than Toyota. She likes fast cars, but has no clue on God’s green earth how they do what they do or why they are fast. One time, I tried to explain (in very simple terms) the difference between whp and crank hp. after about tne minutes, she looked at me and said:

“You mean there is more than one type of horsepower?”

I don’t pay too much attention to 25 hp here and there, because as others have stated, there are too many other variables in vehicle weight, gearing, aerodynamics and frontal area. Not to mention that there are variables from engine to engine (as Quentin pointed out earlier from his findings), vehicle maintenance issues (clean air filter, condition of plugs, etc.), ambient temperature and so forth.

So it’s not something I obsess over…to a point, I tend to recall my many previous vehicles in 25 hp increments: my ‘84 944 had “around 150 hp” and my ‘96 Maxima had “about 200 hp,” but the Corolla I drove in college had “less than 100 hp.” Ah, yes…the Corolla. Drove that thing more aggressively than the highest hp cars I’ve owned, and it kept coming back for more. Of course I was invincible back then…

I would also like to see strict adherence to torque standard measurements and probably find that measurement more meaningful, in absolute terms, than horsepower stats since torque is what gets you moving from a standstill and provides low end pull.

Recently a freind gave me a ride around town in his Ford Model A – 1931 Vintage. He said the engine made 37 horsepower. Most published figures I’ve seen rate it at 40. I’m not going to quibble. What impressed me is that for the most part, the A is quite capable of keeping up with city traffic. Sure, starting off from a stop is a bit slow – you can’t shift real fast, you need to hesitate a bit or it’ll grind. But as far as HP goes, 40 is all that is needed for city driving.

40 of course wouldn’t do it on the highway. I wouldn’t want to merge onto the interstate in a Model A. But adding another 100 HP, as in my Ranger, is more than enough. I therefore can’t get real exicited about the difference between 137 and 152, for example. Both are more than adequate for a compact car or compact PU. That’s assuming that one has outgrown the hotrodder/boy racer phase of life.

I’ve no objection to people buying more HP, if that’s what they want, but the reality is that most American iron is overpowered, considering the actual use it’s put to.

That said, if something is worth doing, it’s worth doing accurately. HP measures should be accurate.

Mechanical horsepower ≡ 33,000 ft·lbf/min
= 550 ft·lbf/s
= 745.6999 W

Metric horsepower ≡ 75 kgf·m/s
= 735.49875 W (exactly)

Electrical horsepower ≡746 W
Boiler horsepower ≡ 33,475 Btu/h
=9809.5 W

Hydraulic horsepower =Flow Rate(US gal/min) * Pressure(psi) / 1714

So what’s the problem? Nobody knows what, if anything, was wrong with the 2 slow cars because C&D didn’t conduct the same tests on them that they did on the “ringers”. Perhaps they had a wonky turbo. If C&D had tested everything and found that the cars all had the claimed 480 hp, would people still be saying that these cars were “ringers” and that customer cars will ship with less? And further, who’s to say that C&D didn’t cock up their testing? That’s just as valid a possibility.

People should wait utnil they see actual dyno #’s from a customer car (I’m sure there’ll be plenty of videos on youtube soon enough), before they take Nissan to task over this one.

The HP and Torque curves should be accurate, and readily available for customers to see.

Do I care that my new GTI’s motor makes 200 hp? Not really, however, I do care that peak torque comes around 1800 RPM and stays until about 5000 RPM. That matters more.

-ted