How do relative HP/Torque ratios affect 0-60 and 1/4mile times? Does anyone have a good explanation in laymans terms?

Thanks,
BK

 

 

Torque is the physical amount of force applied by the engine->tires->street. Horsepower is in laymens terms the amount of times that torque can be applied per rotation of the wheel. So a car can put down 420 lbs of torque at 2000 rpm's but at 4000 rpm's the engine is moving twice as fast so it's able to turn relatively 2 times for every 1 wheel revolution. Horsepower is how well your car is applying this torque basically. All e/t's and 60' times are the result of your average horsepower not torque.

 

First: all else being equal.

The math will be kept to basic minimum

And we're talking curves here, not peak numbers. Peak tells you very little about an engines ability to produce torque through it RPM range.

Torque is a force, in this case a twisting force. Force creates acceleration, F=MA.

Horsepower (power) is force through a distance over time. Power dictates the rate of work and therefore the rate acceleration.

A Torque Curve tells you how much force an engine can produce at any RPM. And torque is directly measured using a dynometer (dyno).

HP is simply calculated from that torque curve using a simple equation.

torque (lb-ft) x RPM
5252

As you can see torque and horsepower are directly related.


If you have either a Power or Torque curve you can figure out what kind of acceleration you would expect to see and at what RPM ranges you would maximize that acceleration.

This is why 2 cars that seem equal either don't accelerate equally or require 2 different launch techniques to get the same results. Again, all else being equal.

All else being equal then the more area is under the curve then the faster the car, under most circumstances. This is why a car with a flat and fat torque curve tends to be fast.

Weight, tires and gearing all make a big difference.


Normally a car that has a low torque rating and high horsepower rating tends to have a shallow and peaky torque curve. Which means that it only kicks in the high RPM range. Ex. Honda S2000.

You can get a high HP number with just high revs, see equation above.

A car that has both peaks numbers low in the RPM range tends to jump off the line but then die at the higher RPM's. Diesels are a perfect example. And they tend to put down a lot of torque, but at a slow rate. Lot's of muscle and work but at a slow rate.

The best (in theory) is a car with a lot's of torque down low in the RPM's and a peak power high in the RPM. This tends to mean that the car make lots of force all through the RPM range and puts down that force at a high rate. I must say the LSx engines are pretty good examples.

 

sweet write up

 

Horsepower is probably the term most used when discussing muscle cars. However, few people can accurately define what exactly horsepower is. Horsepower is officially defined as "the amount of energy required to lift 550 pounds, one foot, in one second." But what does this mean? To answer that question, we need to know a little history.

The term horsepower was created by James Watt, an engineer famous for his work with steam engines and is most associated with his measure of electric power (i.e. 60 watt light bulb). Around 1775, Watt wanted to create a standard measure of work to compare the output of his steam engines with the horses that were used to move large loads in mines. Watt studied the amount of work that horses did and found that on average, a mine horse could perform 22,000 foot-pounds of work in a minute (for example, move 1,000 lbs 22 feet in one minute or 500 pounds 44 feet in one minute). He then increased the number by 50 percent and came up with a measurement of 33,000 foot-pounds of work in one minute. This measurement eventually became known as horsepower.

Using various physics equations, you can come up with different interpretations of horsepower:

1 horsepower is equivalent to 746 watts. So if you took a 1-horsepower horse and put it on a treadmill, it could operate a generator producing a continuous 746 watts.

1 horsepower (over the course of an hour) is equivalent to 2,545 BTU (British thermal units). If you took that 746 watts and ran it through an electric heater for an hour, it would produce 2,545 BTU (where a BTU is the amount of energy needed to raise the temperature of 1 pound of water 1 degree F).

One BTU is equal to 1,055 joules, or 252 gram-calories or 0.252 food Calories. Presumably, a horse producing 1 horsepower would burn 641 Calories in one hour if it were 100-percent efficient.

Types of Horsepower

There are three basic types of horsepower, SAE Gross Horsepower, SAE Net Horsepower, and Wheel Horsepower. Each is the result of measuring the same engine in different ways. These standards were established by the Society of Automotive Engineers (SAE). The SAE is a group responsible for setting various standards within the automobile manufacturing industry. Founded in 1905, the SAE publishes many new, revised, and reaffirmed standards each year in three categories: Ground Vehicle Standards, Aerospace Standards, and Aerospace Material Specifications. Standards allow entire countries to talk to each other in a common language.

SAE Gross Horsepower or Brake horsepower (bhp) was the standard horsepower measurement by the automotive industry up until 1971. Brake Horsepower Power is measured at the flywheel with no load from a chassis or any accessories and with fuel and ignition operations under ideal conditions. An accessory is anything attached to the engine, by any means, which is not required for basic engine operation. By this definition, this would include a power steering pump, smog pump, air conditioning compressor and an alternator. Ideal conditions, often called laboratory conditions, are standardized settings for use during horsepower measurement. During the 1960s they consisted of a barometric pressure of 29.92 Hg and a temperature of 60 degrees F.

SAE Net Horsepower became the standard measurement in 1972, and is still used today. SAE Net horsepower is the horsepower generated by the engine at the flywheel with all accessories attached. This change was made to reflect the numerous energy sapping accessories that cars began to have, such as an A/C Compressor and alternator, and thus was a better representation of the actual power generated by the engine. This number is always lower than the SAE Gross horsepower. Therefore, the same engine could have been rated in 1971 as 360 SAE Gross Horsepower and in 1972 as 300 SAE Net horsepower without any reduction in "power."

Wheel horsepower is horsepower measured at the actual drive wheels, taking into account the load from the chassis and all accessories. It is the most accurate measure of the amount of energy that the car actually generates to move it forward. Wheel horsepower is measured using a dynamometer. This is done by placing the vehicle's driven wheels on a large roller and accelerating the wheels up to redline in first or second gear. The vehicle's ability to turn this roller is measured and calculated (formula below) to come up with a figure that represents how much horsepower is actually available to move the vehicle around. Because a frictional loss between the engine and the driven wheels is unavoidable, wheel-driven horsepower will always be less than SAE Net Horsepower. How much less wheel-driven horsepower will depend on how many mechanical parts exist between a vehicle's engine and its driven wheels. This is usually measured as a percentage loss due to the "friction" of the intermediate components between the flywheel and the actual wheel. For a Rear Wheel Drive car, engine power has to travel through a transmission, driveshaft, rear-differential, and two axle shafts (one for each rear wheel). That's four separate mechanical components taking a bite out of the car's horsepower before the rear wheels even begin to turn. Front-wheel drive cars with transverse-mounted engines usually have a lower frictional loss because horsepower only has to travel from the engine, through the transmission and down two short driveshafts before reaching the wheels. Typical "powertrain" losses run between 15-22% but vary greatly between cars.

Definition of Torque

Torque is a force that tends to rotate or turn things. You generate torque any time you apply a force using a wrench. Tightening the lug nuts on your wheels is a good example. When you use a wrench, you apply a force to the handle. This force creates a torque on the lug nut, which tends to turn the lug nut. Torque is usually measured in English units such as pound-feet (lb-ft), although the international standard is the Newton-meter (1 lb-ft is equal to 1.356 Nm). Notice that the torque units contain a distance and a force. To calculate the torque, you just multiply the force by the distance from the center. In the case of the lug nuts, if the wrench is a foot long, and you put 200 pounds of force on it, you are generating 200 pound-feet of torque. If you use a 2-foot wrench, you only need to put 100 pounds of force on it to generate the same torque.

In a car, the engine converts the horsepower it generates into torque by turning the crank shaft. The combustion of gas in the cylinder creates pressure against the piston. That pressure creates a force on the piston, which pushes it down. The force is transmitted from the piston to the connecting rod, and from the connecting rod into the crankshaft. The point where the connecting rod attaches to the crank shaft is some distance from the center of the shaft. The horizontal distance changes as the crankshaft spins, so the torque also changes, since torque equals force multiplied by distance. Only the horizonal distance is used in determining the torque in an engine. When the piston is at the top of its stroke, the connecting rod points straight down at the center of the crankshaft. No torque is generated in this position, because only the force that acts on the lever in a direction perpendicular to the lever generates a torque.



Dan

 

I fly a airplane, run a company but feel like the dumbest kid in school when it comes to understanding this stuff.

 

I also fly an airplane (Citabria), run a company (Advantage Label) and feel like the dumbest kid in school when it comes to understanding this stuff.

I am just impressed with the fact that all these smart guys tolerate, without being a smart a**, some of our questions.

I will be picking up my 'vette from Lingenfelter with rear wheel dyno numbers of 424.2 HP and 359.1 torque...thought I better understand things a little better.

Thanks for the knowledge gentlemen.

 

Hey guys,

I just wanted to throw my hat in the ring here and point out something that a lot of guys on here may not know. I think it was covered pretty well above, and I am just reinforcing that point.

Peak horsepower and torque numbers are NOT what it's all about. It has a lot to do with your horsepower and torque CURVES. To illustrate, I want to show you some preliminary dyno pulls of my car when it was supercharged vs. the same car now, on a TTi Stage X twin turbo setup (which I installed myself and had my tuner do some adjustments and refabrication of some pipes, as well as work out some bugs).

The blue lines are horsepower and torque for my turbo, red lines are horsepower and torque for the supercharger. Notice how the supercharger applied horsepower almost linearly (faster the motor spun, the faster the blower spun, so horsepower was always increasing).

Notice how the turbo comes on much harder in the early RPMs though. If I could race my old setup against this new setup (and assuming the new setup could put that power down to the street), my new setup would be walking away from the old one pretty well all the way up until about 5500RPM. From there out is just about the only place the blower, which had more peak horsepower, could catch up.

By the time we are done tuning and tweaking the new setup, the blower setup will never have a chance, not ever, throughout the whole RPM band

For you gear-heads that are interested, the TT setup is also running only 8-9psi whereas the blower setup was running 10psi.

Lesson: it's not just about peak numbers, it's also about how your curve looks. And to always just focus on horsepower numbers won't ever tell you the full picture. My TT is making less horsepower than my blower but it will be faster, if it hooks up.

 

torque gets you going, horsepower keeps you going.

 

Very informative...!!!

 

Below was pasted form the site below.
This writeup finally made me understand HP vs. Torque.

Link to Post


There's been a certain amount of discussion, in this and other files, about the concepts of horsepower and torque, how they relate to each other, and how they apply in terms of automobile performance. I have observed that, although nearly everyone participating has a passion for automobiles, there is a huge variance in knowledge. It's clear that a bunch of folks have strong opinions (about this topic, and other things), but that has generally led to more heat than light, if you get my drift :-). I've posted a subset of this note in another string, but felt it deserved to be dealt with as a separate topic. This is meant to be a primer on the subject, which may lead to serious discussion that fleshes out this and other subtopics that will inevitably need to be addressed.
OK. Here's the deal, in moderately plain english.


Force, Work and Time
If you have a one pound weight bolted to the floor, and try to lift it with one pound of force (or 10, or 50 pounds), you will have applied force and exerted energy, but no work will have been done. If you unbolt the weight, and apply a force sufficient to lift the weight one foot, then one foot pound of work will have been done. If that event takes a minute to accomplish, then you will be doing work at the rate of one foot pound per minute. If it takes one second to accomplish the task, then work will be done at the rate of 60 foot pounds per minute, and so on.
In order to apply these measurements to automobiles and their performance (whether you're speaking of torque, horsepower, newton meters, watts, or any other terms), you need to address the three variables of force, work and time.

Awhile back, a gentleman by the name of Watt (the same gent who did all that neat stuff with steam engines) made some observations, and concluded that the average horse of the time could lift a 550 pound weight one foot in one second, thereby performing work at the rate of 550 foot pounds per second, or 33,000 foot pounds per minute, for an eight hour shift, more or less. He then published those observations, and stated that 33,000 foot pounds per minute of work was equivalent to the power of one horse, or, one horsepower.

Everybody else said OK. :-)

For purposes of this discussion, we need to measure units of force from rotating objects such as crankshafts, so we'll use terms which define a *twisting* force, such as foot pounds of torque. A foot pound of torque is the twisting force necessary to support a one pound weight on a weightless horizontal bar, one foot from the fulcrum.

Now, it's important to understand that nobody on the planet ever actually measures horsepower from a running engine. What we actually measure (on a dynomometer) is torque, expressed in foot pounds (in the U.S.), and then we *calculate* actual horsepower by converting the twisting force of torque into the work units of horsepower.

Visualize that one pound weight we mentioned, one foot from the fulcrum on its weightless bar. If we rotate that weight for one full revolution against a one pound resistance, we have moved it a total of 6.2832 feet (Pi * a two foot circle), and, incidently, we have done 6.2832 foot pounds of work.

OK. Remember Watt? He said that 33,000 foot pounds of work per minute was equivalent to one horsepower. If we divide the 6.2832 foot pounds of work we've done per revolution of that weight into 33,000 foot pounds, we come up with the fact that one foot pound of torque at 5252 rpm is equal to 33,000 foot pounds per minute of work, and is the equivalent of one horsepower. If we only move that weight at the rate of 2626 rpm, it's the equivalent of 1/2 horsepower (16,500 foot pounds per minute), and so on. Therefore, the following formula applies for calculating horsepower from a torque measurement:


Torque * RPM

Horsepower = ------------

5252


This is not a debatable item. It's the way it's done. Period.
The Case For Torque
Now, what does all this mean in carland?
First of all, from a driver's perspective, torque, to use the vernacular, RULES :-). Any given car, in any given gear, will accelerate at a rate that *exactly* matches its torque curve (allowing for increased air and rolling resistance as speeds climb). Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it. Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300 foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear, yet, per the formula, the horsepower would be *double* at 4000 rpm. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same.

In contrast to a torque curve (and the matching pushback into your seat), horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, until well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver *feels*.

You don't believe all this?

Fine. Take your non turbo car (turbo lag muddles the results) to its torque peak in first gear, and punch it. Notice the belt in the back? Now take it to the power peak, and punch it. Notice that the belt in the back is a bit weaker? Fine. Can we go on, now? :-)


The Case For Horsepower
OK. If torque is so all-fired important, why do we care about horsepower?
Because (to quote a friend), "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*.

For an extreme example of this, I'll leave carland for a moment, and describe a waterwheel I got to watch awhile ago. This was a pretty massive wheel (built a couple of hundred years ago), rotating lazily on a shaft which was connected to the works inside a flour mill. Working some things out from what the people in the mill said, I was able to determine that the wheel typically generated about 2600(!) foot pounds of torque. I had clocked its speed, and determined that it was rotating at about 12 rpm. If we hooked that wheel to, say, the drivewheels of a car, that car would go from zero to twelve rpm in a flash, and the waterwheel would hardly notice :-).

On the other hand, twelve rpm of the drivewheels is around one mph for the average car, and, in order to go faster, we'd need to gear it up. To get to 60 mph would require gearing the wheel up enough so that it would be effectively making a little over 43 foot pounds of torque at the output, which is not only a relatively small amount, it's less than what the average car would need in order to actually get to 60. Applying the conversion formula gives us the facts on this. Twelve times twenty six hundred, over five thousand two hundred fifty two gives us:

6 HP.

Oops. Now we see the rest of the story. While it's clearly true that the water wheel can exert a *bunch* of force, its *power* (ability to do work over time) is severely limited.


At The Dragstrip
OK. Back to carland, and some examples of how horsepower makes a major difference in how fast a car can accelerate, in spite of what torque on your backside tells you :-).
A very good example would be to compare the current LT1 Corvette with the last of the L98 Vettes, built in 1991. Figures as follows:


Engine Peak HP @ RPM Peak Torque @ RPM

------ ------------- -----------------

L98 250 @ 4000 340 @ 3200

LT1 300 @ 5000 340 @ 3600


The cars are geared identically, and car weights are within a few pounds, so it's a good comparison.
First, each car will push you back in the seat (the fun factor) with the same authority - at least at or near peak torque in each gear. One will tend to *feel* about as fast as the other to the driver, but the LT1 will actually be significantly faster than the L98, even though it won't pull any harder. If we mess about with the formula, we can begin to discover exactly *why* the LT1 is faster. Here's another slice at that formula:


Horsepower * 5252

Torque = -----------------

RPM


If we plug some numbers in, we can see that the L98 is making 328 foot pounds of torque at its power peak (250 hp @ 4000), and we can infer that it cannot be making any more than 263 pound feet of torque at 5000 rpm, or it would be making more than 250 hp at that engine speed, and would be so rated. In actuality, the L98 is probably making no more than around 210 pound feet or so at 5000 rpm, and anybody who owns one would shift it at around 46-4700 rpm, because more torque is available at the drive wheels in the next gear at that point.
On the other hand, the LT1 is fairly happy making 315 pound feet at 5000 rpm, and is happy right up to its mid 5s redline.

So, in a drag race, the cars would launch more or less together. The L98 might have a slight advantage due to its peak torque occuring a little earlier in the rev range, but that is debatable, since the LT1 has a wider, flatter curve (again pretty much by definition, looking at the figures). From somewhere in the mid range and up, however, the LT1 would begin to pull away. Where the L98 has to shift to second (and throw away torque multiplication for speed), the LT1 still has around another 1000 rpm to go in first, and thus begins to widen its lead, more and more as the speeds climb. As long as the revs are high, the LT1, by definition, has an advantage.

Another example would be the LT1 against the ZR-1. Same deal, only in reverse. The ZR-1 actually pulls a little harder than the LT1, although its torque advantage is softened somewhat by its extra weight. The real advantage, however, is that the ZR-1 has another 1500 rpm in hand at the point where the LT1 has to shift.

There are numerous examples of this phenomenon. The Integra GS-R, for instance, is faster than the garden variety Integra, not because it pulls particularly harder (it doesn't), but because it pulls *longer*. It doesn't feel particularly faster, but it is.

A final example of this requires your imagination. Figure that we can tweak an LT1 engine so that it still makes peak torque of 340 foot pounds at 3600 rpm, but, instead of the curve dropping off to 315 pound feet at 5000, we extend the torque curve so much that it doesn't fall off to 315 pound feet until 15000 rpm. OK, so we'd need to have virtually all the moving parts made out of unobtanium :-), and some sort of turbocharging on demand that would make enough high-rpm boost to keep the curve from falling, but hey, bear with me.

If you raced a stock LT1 with this car, they would launch together, but, somewhere around the 60 foot point, the stocker would begin to fade, and would have to grab second gear shortly thereafter. Not long after that, you'd see in your mirror that the stocker has grabbed third, and not too long after that, it would get fourth, but you'd wouldn't be able to see that due to the distance between you as you crossed the line, *still in first gear*, and pulling like crazy.

I've got a computer simulation that models an LT1 Vette in a quarter mile pass, and it predicts a 13.38 second ET, at 104.5 mph. That's pretty close (actually a tiny bit conservative) to what a stock LT1 can do at 100% air density at a high traction drag strip, being powershifted. However, our modified car, while belting the driver in the back no harder than the stocker (at peak torque) does an 11.96, at 135.1 mph, all in first gear, of course. It doesn't pull any harder, but it sure as hell pulls longer :-). It's also making *900* hp, at 15,000 rpm.

Of course, folks who are knowledgeable about drag racing are now openly snickering, because they've read the preceeding paragraph, and it occurs to them that any self respecting car that can get to 135 mph in a quarter mile will just naturally be doing this in less than ten seconds. Of course that's true, but I remind these same folks that any self-respecting engine that propels a Vette into the nines is also making a whole bunch more than 340 foot pounds of torque.

That does bring up another point, though. Essentially, a more "real" Corvette running 135 mph in a quarter mile (maybe a mega big block) might be making 700-800 foot pounds of torque, and thus it would pull a whole bunch harder than my paper tiger would. It would need slicks and other modifications in order to turn that torque into forward motion, but it would also get from here to way over there a bunch quicker.

On the other hand, as long as we're making quarter mile passes with fantasy engines, if we put a 10.35:1 final-drive gear (3.45 is stock) in our fantasy LT1, with slicks and other chassis mods, we'd be in the nines just as easily as the big block would, and thus save face :-). The mechanical advantage of such a nonsensical rear gear would allow our combination to pull just as hard as the big block, plus we'd get to do all that gear banging and such that real racers do, and finish in fourth gear, as God intends. :-)

The only modification to the preceeding paragraph would be the polar moments of inertia (flywheel effect) argument brought about by such a stiff rear gear, and that argument is outside of the scope of this already massive document. Another time, maybe, if you can stand it :-).


At The Bonneville Salt Flats
Looking at top speed, horsepower wins again, in the sense that making more torque at high rpm means you can use a stiffer gear for any given car speed, and thus have more effective torque *at the drive wheels*.
Finally, operating at the power peak means you are doing the absolute best you can at any given car speed, measuring torque at the drive wheels. I know I said that acceleration follows the torque curve in any given gear, but if you factor in gearing vs car speed, the power peak is *it*. An example, yet again, of the LT1 Vette will illustrate this. If you take it up to its torque peak (3600 rpm) in a gear, it will generate some level of torque (340 foot pounds times whatever overall gearing) at the drive wheels, which is the best it will do in that gear (meaning, that's where it is pulling hardest in that gear).

However, if you re-gear the car so it is operating at the power peak (5000 rpm) *at the same car speed*, it will deliver more torque to the drive wheels, because you'll need to gear it up by nearly 39% (5000/3600), while engine torque has only dropped by a little over 7% (315/340). You'll net a 29% gain in drive wheel torque at the power peak vs the torque peak, at a given car speed.

Any other rpm (other than the power peak) at a given car speed will net you a lower torque value at the drive wheels. This would be true of any car on the planet, so, theoretical "best" top speed will always occur when a given vehicle is operating at its power peak.

"Modernizing" The 18th Century
OK. For the final-final point (Really. I Promise.), what if we ditched that water wheel, and bolted an LT1 in its place? Now, no LT1 is going to be making over 2600 foot pounds of torque (except possibly for a single, glorious instant, running on nitromethane), but, assuming we needed 12 rpm for an input to the mill, we could run the LT1 at 5000 rpm (where it's making 315 foot pounds of torque), and gear it down to a 12 rpm output. Result? We'd have over *131,000* foot pounds of torque to play with. We could probably twist the whole flour mill around the input shaft, if we needed to :-).

The Only Thing You Really Need to Know
Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." :-)