James Bailey

From How stuff Works...." **Have you ever looked at the specs of an engine in a magazine and seen something like "this engine makes 300 pound-feet of torque at 4,000 RPM," and wondered how much power that was? How much horsepower are we talking about here? You can calculate how many foot-pounds of horsepower this engine produces using a common equation:

The engine that makes 300 pound-feet of torque at 4,000 RPM produces [(300 x 4,000) / 5,252] 228 horsepower at 4,000 RPM. But where does the number 5,252 come from?

To get from pound-feet of torque to horsepower, you need to go through a few conversions. The number 5,252 is the result of lumping several different conversion factors together into one number.

First, 1 horsepo*wer is defined as 550 foot-pounds per second (read How Horsepower Works to find out how they got that number). The units of torque are pound-feet. So to get from torque to horsepower, you need the "per second" term. You get that by multiplying the torque by the engine speed.

But engine speed is normally referred to in revolutions per minute (RPM). Since we want a "per second," we need to convert RPMs to "something per second." The seconds are easy -- we just divide by 60 to get from minutes to seconds. Now what we need is a dimensionless unit for revolutions: a radian. A radian is actually a ratio of the length of an arc divided by the length of a radius, so the units of length cancel out and you're left with a dimensionless measure.

*You can think of a revolution as a measurement of an angle. One revolution is 360 degrees of a circle. Since the circumference of a circle is (2 x pi x radius), there are 2-pi radians in a revolution. To convert revolutions per minute to radians per second, you multiply RPM by (2-pi/60), which equals 0.10472 radians per second. This gives us the "per second" we need to calculate horsepower.

Let's put this all together. We need to get to horsepower, which is 550 foot-pounds per second, using torque (pound-feet) and engine speed (RPM). If we divide the 550 foot-pounds by the 0.10472 radians per second (engine speed), we get 550/0.10472, which equals 5,252.

So if you multiply torque (in pound-feet) by engine speed (in RPM) and divide the product by 5,252, RPM is converted to "radians per second" and you can get from torque to horsepower -- from "pound-feet" to "foot-pounds per second.".................

So if One horsepower is 550 ft lbs per second, what is there to discuss ??? the difference between "pound feet" and "foot-pounds per second"

mark kibort

as was stated the answer is simple . driver and gearing. at that particular speed, we dont know what gear Rick was in, but probably the wrong one, plus you had a jump on the start (driver). the proof is in the times. they reflect drivers were near the same , and cars as well. sure you have a weight deficit, but if you look at ricks car, its not set up as low as yours, which can almost neutralize a 100-200lb difference. (i.e. 1 second a lap, if all other thing are equal). so many factors, so little time!

take a look at the guys I run with week after week. they all have the same HP weight (520rwhp and 3000lbs) while I have 370rwhp and 3000lbs.

take a look.

IcemanG17

Rick did beat me for fast lap of the weekend....he ran .05 of a second faster..... he also won the 1st race......I won the 2nd race, but it was HOT HOT HOT and my lap times were about 2 seconds off both of our best times.....

It will be interesting to see how the Estate handles with its new wheels & slicks

mark kibort

The bottom line here, yet again, is HP incorporates torque. it just gives/has a little more information. (actually double the info!). nothing wrong with torque/force, but HP is easier to work with, primarily to compare performance of dissimilar torque engines with near the same hp.
in the end, its all about how much power you can put down to the ground over a distance and speed.
if you ever put down the same hp as someone else (all other things being the the same) you will accelerate exactly the same regardless of engine torque and RPM. Not my law, its newton's!

acceleration = Power/(mass x velocity) acceleration is DIRECTLY proportional to power.

Strosek Ultra

Here is a low torque, high horsepower, high reving Judd V8 race engine of the European school. 3,4 Ltr., 560 Hp, 10.000 rpm. Unfortunately the driver Georg Plasa had a fatal crash in this car. When will we see a high reving 928 race engine?

Ake

Carl Fausett

The HP vs Torque question is not a clear one, and will never lend itself to a simple B&W answer.

Crew chiefs spend time doing the math on each race course to compute the area under the HP curve in each section of a race track just to set the right gear ratios. The idea being that the drop in revs from one gear up to the next must capture the maximum available HP and torque for the next gear, or speed is lost. Reference Carroll Smith's "Tune to Win" for more information.

There are many, many variables to the HP vs Torque discussion that are usually (conveniently) left out. The gear ratios, the mass of the drivetrain (more significant than you think), the transmission type, the diameter of the tires, the coefficient of drag of the vehicle, track incline, number and tightness of the corners, and more.

All you can fairly say is this: that the standing start from zero favors torque, and that the top end is limited by HP. Everything in the middle is some combination of both, in varying degrees.

EspritS4s

Good points, and your last paragraph is a good way to some it up for someone looking for a simple answer. Part of the problem in these threads is that people try to over simplify the discussion and / or make blanket statements. This makes it easy to argue on and on and on and ...

IcemanG17

Well said.....makes sense since so many drag racers like big displacement engines (torque) and-or boost (again more torque)....

it all comes down to how the engine is built & what its goals are! Since the basic rules of getting more HP & torque never change:

1: More displacement
2: More RPM
3: Boost

another HUGE factor is how long the engine is designed to last and under what type of conditions! The 928 engine has proven extremely reliable under street conditions and so-so on track, which is about the harshest conditions imaginable, except for maybe ORR

I plan on conducting a clinic on TORQUE this weekend at Sears Point with my fellow "lemons" racers........

bcdavis

Well, I guess my Kibort challenge didn't work...

Anyhow, in previous debates, I still contend that there can be a distinction between the
two words, because they don't have to be based on the scientific definition of "torque"
or "horsepower". People get caught up in semantics. People still know there is a
difference between an engine that "pushes them back in the seat", versus one
that accelerates slowly, but when it hits high RPM, builds up a tremendous amount
of power and acceleration. And that can be as simple as gearing. Could even
be the exact same engine. But if it has a specific rear end, specific transmission,
tires, etc, then it can accelerate very forcefully off the line, which people equate
to the word "torque". And they aren't talking about the scientific definition.
They are talking about specific cars being capable of putting a large amount
of power to the ground at low RPM. That's what people consider "torque".
And most people know that torque gets you off the line quickly, and it helps
you accelerate out of corners. If your car has massive horsepower on paper,
but low torque off the line, we know that horsepower is probably at the high
end of the curve, where it's not as effective at getting the car off the line,
or out of a corner. Mainly because the car needs higher RPMs to get it
into the powerband. My main point is that we know that there is a scientific
formula for hp/tq. But most people aren't concerned with the science.
They are concerned with real-world experiences. How a car works
on the race track... And yes, perhaps a specific BMW engine can
rev to 10,000 RPM and make 500 hp. But we also know that if we
are on a racetrack, we might prefer a Dodge Viper with 600 tq.
Because we know that power will be available for a wider range
of the powerband, and at lower RPM, making the car easier to
drive. Now that number might come because of gearing, displacement,
cams, or any number of things. But it's the results people care about.
How easy is the car to drive, and which car is faster around the track?

The better question really would be:

"Do you think a car with power in the high RPM range is faster around a racetrack than a car with power in the low RPM range?"

Glenn Evans

Do you mean torque in the low RPM range?

IcemanG17

The easy answer is its the same....assuming the low torque car has proper gearing.....and an engine that can spin some RPM's (typical for low torque motors)......then the higher speed engine makes up for its low torque by more time in lower gears which mulitply its torque for the same acceleration....

An example...my old M3 with 4L of displacement, but the ability to spin 8400rpm made 270ftlbs on the dyno....BUT it made it from 3000 to 8000 rpm....however having 7 gears made it never-ever drop below 6000rpm on track...so it was between 300-400whp all the time

EspritS4s

I left Rennlist and switched over to TractorByNet (I'm shopping for a mower/snow blower/tractor) and what do I find?

http://www.tractorbynet.com/forums/r...vs-torque.html

I suppose this debate must exist on any forum dedicated to anything driven by a motor.

inactiveuser1

Thats why i gave the 2 cars as an example on how they run.
Look at a GT3 RS 4.0 being 2998lbs in weight 500hp
500 hp 8,250
Max. torque at rpm
339 lb.-ft. 5,750
Curb weight
2,998 lbs


997TT 500 hp
500hp@ rpm 6,000 - 6,500 rpm
Torque
480 lb.-ft. (with overboost 516 lb.-ft.)
@ rpm
1,950 - 5,000 rpm (with overboost 2,100 - 4,000 rpm)

997TT is 500lbs heavier and torque & hp comes in way earlier the car accelerates quicker
Getting both the HP and torque in the earlier RPM range is the most important if you have the traction like all AWD TT car.
They both have same HP but maximum torque is different!
Depends on the application they are used for where you need the torque and maximum hp.

RKD in OKC

Half empty, half full...what really matters is the size of the glass.

mark kibort

not really carl. the size of tires, speed aroud corners, mass of drivetrain especially, drag, etc, all favor power , which is a rate of doing work. TORQUE is just half the factor of HP. HP contains more. sure its torque that does the work, but its the torque at the rear wheels that you are concerned with, and thats determined by HP . this is precicely why folks as well as Carrol that you mention, take the mystery of it all out, by looking at HP curves and just making sure that your post shift HP is equal to your pre shift hp.

standing starts excluded as this is a pure torque , but certainly hp thing too, given that at ANY vehicle speed, acceleration is directly proportional to power, OR rear wheel torque. acceleration= power/(mass x velocity)

top end is limited and determined by HP , torque at the rear wheels as well. coming off a turn is limited and determined by HP and torque at the wheels to the same degree. power IS torque and speed. HP , inextricably ties torque TO RPM , and power to force and vehicle speed. its that simple.

HP gives the information you need to compare two cars with disparate engine torque characteristics. its just much easier to work with. both torque and HP are correct for determining rear wheel forces, just HP makes it easier to compare.

once you get this clear in your mind, the things like drive train weight, (which only effects HP when acceleration rates ar VERY very fast, like engine reving in neutral, or only really in 1st gear) you realize what really matters .

to race a car in a straight line, out of turns, down a straight, you want to acceleratate as fast as possible, and this requires HP! (whch gives rear wheel torque, not related or dictated by engine torque high values)