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T88H34GSUPRA · 08-19-2003, 07:40 PM

Just so you don't sound like a complete idiot in future discussions... You should learn the difference between horsepower and torque and what the signifigance of each one is in relationship to how a car goes down a drag strip.

Definition of Horsepower and Torque:

One HP is defined as being 33,000 foot pounds per minute of energy. This means ONE Horsepower is sufficient to move ONE POUND 33,000 feet in one minutes time. Or it can also mean that it can move 33,000 POUNDS one single foot, in one minute. It just depends on how you do the math.

This is true because regardless of gearing (or mechanical advantage), one horsepower is always one horsepower, gearing never changes that. This is because Horsepower is a combination of FORCE, WORK, and TIME.

FORCE, WORK, TIME: If you were to try and push a 2,000 pound car, with it's parking brake engaged, with all your strength, which lets say is 100 pounds of FORCE. You are applying force, but not doing any work (because the car won't move). If you were to release the brake, and now beable to push the car with your 100 pounds of force for 1 single foot, then you have now done WORK. If it took you 1 MINUTE to do that work, then you have done work at the rate of 100 foot-pounds per minute. If you were able to move the car 2 feet in one minute with your 100 pounds of force, the you have done the work at the rate of 200 foot-pounds per minute.

Now we need to apply this to automotive use. In the automotive world, force and work are delivered in a rotating form (such as the crankshaft, driveshaft, or wheels). This TWISTING force is defined at Torque. In torque, ONE FOOT-POUND is the force needed to suspend a one pound weight, horizontally from a point one foot from the fulcrum (center of the rotation). If this point was moved to 10 FEET from the fulcrum, then that one pound weight has gained mechanical advantage, it now requires TEN FOOT-POUNDS too support that weight. This would be the same twisting force as a TEN pound weight being suspended from the original 1 foot distance from the center of rotation.

To see the effects of mechanical advantage for yourself, hold your arm out horizontally, and suspend a 5 pound weight mid way from your arm, now move that weight to your hand, it feels twice as heavy, because it has gained mechanical advantage (leverage).

But understand, that 5 pound weight hanging from your arm is exerting no more power as before, it is gaining leverage, but in return giving up how quickly it can perform actual work. Lets say that 5 pound weight was applying enough force that the weight could move 1 foot in one second. If that one foot of movement occurred at the middle of your arm, it would cause your arm to have rotated more, than if the one foot distance was only at the tip of your arm. That's mechanical advantage, and how the "Gearing" works in your car, both the transmission and axle. To gain speed (work rate), you have to sacrifice force. But we will come back to this later.

We were talking about torque, and how it is "twisting" force. Now Horsepower would be a combination of Torque, and how quickly torque can be delivered, which is a combination of work and the time it took to perform that work, which in this case can be expressed at RPM. So now we have two things, Torque (our force), and RPM (the rate the force can be delivered, Revolutions Per Minute). Horsepower is simply the culmination of these two things. Here is how Horsepower is calculated from Torque and RPM:

Torque times RPM divided by 5252 = Horsepower

(One interesting note, on any dyno chart for an engine, the torque and horsepower numbers always cross at 5252 rpms, this is because both 5252s simply cross each other out as they are divided into one another.)

Now we know what Torque and Horsepower are, which is all fine and dandy, but how does this make my car go. Believe it or not, the only thing that causes the car to accelerate is TORQUE, it is that force that pushes your car. Without that force, your car would just sit there, it doesn't matter if the engine is spinning at 15,000 RPMs, if it has no force behind those rotations, it would instantly stall once the clutch was engaged, and the car would go nowhere. Your simply delivering NO FORCE very quickly. But with torque, you have force to push the car, and give some real power to those 15,000rpms.

But also, if you had 1,000 foot-pounds of torque available to you, but no way to deliver it (RPM) then the car would still just sit there. You have to have both to get any work done, and that's what horsepower is.

Since torque is what actually causes acceleration, in any given gear, the car will always accelerate hardest at the torque peak, not the horsepower peak. And this also means that because of mechanical advantage, you car will always accelerate hardest (if traction allows) in the lowest gear. Because the gear reduction is giving the wheels more torque. But if you want to go faster than the engine will allow, then you upshift to a higher gear, and therefore give up some of your mechanical advantage in exchange for a higher work rate. This happens every time you up shift.

And that is why it's good to have lots of horsepower. Because the horsepower peak is when you have the highest culmination of Torque (force) and RPM (rate of work). The higher horsepower means that you can supply the rear wheels with lots of torque, and you can deliver it at a high rate. And not have to upshift as early and loose some of that torque. So while an engine with say 500ft-lbs of peak torque at 2000rpms, but only 250hp by 4000rpm, will pull harder in first gear (All things equal except engine) than an engine with only a peak of 400ft-lbs of torque @ 4000rpm. But if that lower torque engine has a higher horsepower output, then it will start to pull away more and more as speed increases. Lets say that smaller engine puts out a peak of 400hp at 7000rpm. So now lets see what we have...

Smaller Engine 400hp @ 7000rpm 400ft-lbs @ 4000rpm
Big Engine 250hp @ 4000rpm 500ft-lbs @ 2000rpm

Ok, now lets chart out the power bands: RPM 1k 2k 3k 4k 5k 6k 7k
Smaller Engine 200ft-lbs (38hp) 270ft-lbs (103hp) 350ft-lbs (200hp) 400ft-lbs (305hp) 370ft-lbs (352hp) 350ft-lbs (399hp) 300ft-lbs (400hp)

Big Engine 380ft-lbs (72hp) 500ft-lbs (190hp) 400ft-lbs (228hp) 328ft-lbs (250hp) redline

Now as you can see the Big Engine has a distinct advantage up to 3000rpms, after that, the smaller one surpasses it. The Big Engine also wont even rev past 4000rpm. So what does this mean? We'll, if both these engines were in the same type of car, with the same gearing. Then if they both raced side by side, the big engined car would easily pull away off the line, and would continue to pull till he reached a little over 3000rpm. At this point, the smaller, but higher output engine would just begin to make its real power. By 4000, the big engine car has to up shift to 2nd gear, and the resulting change in gearing means that even though it is back at it's torque peak, it is actually putting less torque to the ground than the smaller engine car, which since it can rev higher, is still in 1st gear, and enjoying more gear reduction. And as they keep up shifting and going faster, the difference will only get more pronounced.

An interesting note however. Is that because the smaller engine is higher revving, it can run more gear reduction. Meaning that if the smaller engine was allowed to take advantage of more gear reduction, it would have stayed right beside the big engine car right from the launch, and once the smaller engine has hit it's torque peak, it is putting out more peak torque to the ground than the big engine that puts out more torque at it's engine, but does not have as much gear reduction.

Lets what what gear reduction does to both the cars, shall we. I will display the total gear reduction, which would be the gear ratio of whatever gear you are in in the transmission, multiplied by the gear ratio of the final drive in the differential. I will also include the "gearing-up" caused by the diameter of the drive tires/wheels. Which in this case is 24 inches in total diameter, which means the radius is only 1-foot, so our force at the contact patch, is the same as the wheels torque. So below I will be displaying the actual force being applied at the tires contact patch. Ground Speed 6mph 12mph 17mph 23mph 29mph 35mph 41mph
Smaller Engine 200ft-lbs @ 1000rpm 270ft-lbs @ 2000rpm 350ft-lbs @ 3000rpm 400ft-lbs @ 4000rpm 370ft-lbs @ 5000rpm 350ft-lbs @ 6000rpm 300ft-lbs @ 7000rpm

Force at ground, With 12.3:1 total gear reduction 2460lbs of force 3321lbs of force 4305lbs of force 4920lbs of force 4551lbs of force 4305lbs of force 3690lbs of force

Big Engine 200ft-lbs @ 570rpm 390 ft-lbs @ 1100rpm 480ft-lbs @ 1700rpm 470ft-lbs @ 2300rpm 410ft-lbs @ 2900rpm 360ft-lbs @ 3400rpm 328ft-lbs @ 4000rpm

Force at ground, With 7.0:1 total gear reduction 1400 lbs of force 2730lbs of force 3360lbs of force 3290 lbs of force 2870lbs of force 2520lbs of force 2296lbs of force

You can see how the gearing really helped out the smaller engine. Now the force you see shown in the chart, is what is actually causing the car to accelerate, that's the actual force coming in contact with the ground and pushing the car.

Now if we average the lbs of force listed in the chart, the Big engine comes out at an average of 2638lbs (in first gear). But the well geared, higher HP, Small motor, shows a whopping average of 3936lbs. And the average output has a more direct effect on acceleration than just peaks numbers, which may only remain at that peak for a very short period. So now you can see how that smaller engine, with more HP, but less torque, can really lay down the smack on the bigger torquier engine.

So in summary, Torque is twisting force (cause of acceleration), RPM is work rate (Allows Speed), and Horsepower is the culmination of both (Torque times the rate it is delivered).

Have a nice day.

08-19-2003, 07:40 PM	#48
T88H34GSUPRA Registered Member Join Date: Aug 2003 Location: noplace Posts: 19	Just so you don't sound like a complete idiot in future discussions... You should learn the difference between horsepower and torque and what the signifigance of each one is in relationship to how a car goes down a drag strip. Definition of Horsepower and Torque: One HP is defined as being 33,000 foot pounds per minute of energy. This means ONE Horsepower is sufficient to move ONE POUND 33,000 feet in one minutes time. Or it can also mean that it can move 33,000 POUNDS one single foot, in one minute. It just depends on how you do the math. This is true because regardless of gearing (or mechanical advantage), one horsepower is always one horsepower, gearing never changes that. This is because Horsepower is a combination of FORCE, WORK, and TIME. FORCE, WORK, TIME: If you were to try and push a 2,000 pound car, with it's parking brake engaged, with all your strength, which lets say is 100 pounds of FORCE. You are applying force, but not doing any work (because the car won't move). If you were to release the brake, and now beable to push the car with your 100 pounds of force for 1 single foot, then you have now done WORK. If it took you 1 MINUTE to do that work, then you have done work at the rate of 100 foot-pounds per minute. If you were able to move the car 2 feet in one minute with your 100 pounds of force, the you have done the work at the rate of 200 foot-pounds per minute. Now we need to apply this to automotive use. In the automotive world, force and work are delivered in a rotating form (such as the crankshaft, driveshaft, or wheels). This TWISTING force is defined at Torque. In torque, ONE FOOT-POUND is the force needed to suspend a one pound weight, horizontally from a point one foot from the fulcrum (center of the rotation). If this point was moved to 10 FEET from the fulcrum, then that one pound weight has gained mechanical advantage, it now requires TEN FOOT-POUNDS too support that weight. This would be the same twisting force as a TEN pound weight being suspended from the original 1 foot distance from the center of rotation. To see the effects of mechanical advantage for yourself, hold your arm out horizontally, and suspend a 5 pound weight mid way from your arm, now move that weight to your hand, it feels twice as heavy, because it has gained mechanical advantage (leverage). But understand, that 5 pound weight hanging from your arm is exerting no more power as before, it is gaining leverage, but in return giving up how quickly it can perform actual work. Lets say that 5 pound weight was applying enough force that the weight could move 1 foot in one second. If that one foot of movement occurred at the middle of your arm, it would cause your arm to have rotated more, than if the one foot distance was only at the tip of your arm. That's mechanical advantage, and how the "Gearing" works in your car, both the transmission and axle. To gain speed (work rate), you have to sacrifice force. But we will come back to this later. We were talking about torque, and how it is "twisting" force. Now Horsepower would be a combination of Torque, and how quickly torque can be delivered, which is a combination of work and the time it took to perform that work, which in this case can be expressed at RPM. So now we have two things, Torque (our force), and RPM (the rate the force can be delivered, Revolutions Per Minute). Horsepower is simply the culmination of these two things. Here is how Horsepower is calculated from Torque and RPM: Torque times RPM divided by 5252 = Horsepower (One interesting note, on any dyno chart for an engine, the torque and horsepower numbers always cross at 5252 rpms, this is because both 5252s simply cross each other out as they are divided into one another.) Now we know what Torque and Horsepower are, which is all fine and dandy, but how does this make my car go. Believe it or not, the only thing that causes the car to accelerate is TORQUE, it is that force that pushes your car. Without that force, your car would just sit there, it doesn't matter if the engine is spinning at 15,000 RPMs, if it has no force behind those rotations, it would instantly stall once the clutch was engaged, and the car would go nowhere. Your simply delivering NO FORCE very quickly. But with torque, you have force to push the car, and give some real power to those 15,000rpms. But also, if you had 1,000 foot-pounds of torque available to you, but no way to deliver it (RPM) then the car would still just sit there. You have to have both to get any work done, and that's what horsepower is. Since torque is what actually causes acceleration, in any given gear, the car will always accelerate hardest at the torque peak, not the horsepower peak. And this also means that because of mechanical advantage, you car will always accelerate hardest (if traction allows) in the lowest gear. Because the gear reduction is giving the wheels more torque. But if you want to go faster than the engine will allow, then you upshift to a higher gear, and therefore give up some of your mechanical advantage in exchange for a higher work rate. This happens every time you up shift. And that is why it's good to have lots of horsepower. Because the horsepower peak is when you have the highest culmination of Torque (force) and RPM (rate of work). The higher horsepower means that you can supply the rear wheels with lots of torque, and you can deliver it at a high rate. And not have to upshift as early and loose some of that torque. So while an engine with say 500ft-lbs of peak torque at 2000rpms, but only 250hp by 4000rpm, will pull harder in first gear (All things equal except engine) than an engine with only a peak of 400ft-lbs of torque @ 4000rpm. But if that lower torque engine has a higher horsepower output, then it will start to pull away more and more as speed increases. Lets say that smaller engine puts out a peak of 400hp at 7000rpm. So now lets see what we have... Smaller Engine 400hp @ 7000rpm 400ft-lbs @ 4000rpm Big Engine 250hp @ 4000rpm 500ft-lbs @ 2000rpm Ok, now lets chart out the power bands: RPM 1k 2k 3k 4k 5k 6k 7k Smaller Engine 200ft-lbs (38hp) 270ft-lbs (103hp) 350ft-lbs (200hp) 400ft-lbs (305hp) 370ft-lbs (352hp) 350ft-lbs (399hp) 300ft-lbs (400hp) Big Engine 380ft-lbs (72hp) 500ft-lbs (190hp) 400ft-lbs (228hp) 328ft-lbs (250hp) redline Now as you can see the Big Engine has a distinct advantage up to 3000rpms, after that, the smaller one surpasses it. The Big Engine also wont even rev past 4000rpm. So what does this mean? We'll, if both these engines were in the same type of car, with the same gearing. Then if they both raced side by side, the big engined car would easily pull away off the line, and would continue to pull till he reached a little over 3000rpm. At this point, the smaller, but higher output engine would just begin to make its real power. By 4000, the big engine car has to up shift to 2nd gear, and the resulting change in gearing means that even though it is back at it's torque peak, it is actually putting less torque to the ground than the smaller engine car, which since it can rev higher, is still in 1st gear, and enjoying more gear reduction. And as they keep up shifting and going faster, the difference will only get more pronounced. An interesting note however. Is that because the smaller engine is higher revving, it can run more gear reduction. Meaning that if the smaller engine was allowed to take advantage of more gear reduction, it would have stayed right beside the big engine car right from the launch, and once the smaller engine has hit it's torque peak, it is putting out more peak torque to the ground than the big engine that puts out more torque at it's engine, but does not have as much gear reduction. Lets what what gear reduction does to both the cars, shall we. I will display the total gear reduction, which would be the gear ratio of whatever gear you are in in the transmission, multiplied by the gear ratio of the final drive in the differential. I will also include the "gearing-up" caused by the diameter of the drive tires/wheels. Which in this case is 24 inches in total diameter, which means the radius is only 1-foot, so our force at the contact patch, is the same as the wheels torque. So below I will be displaying the actual force being applied at the tires contact patch. Ground Speed 6mph 12mph 17mph 23mph 29mph 35mph 41mph Smaller Engine 200ft-lbs @ 1000rpm 270ft-lbs @ 2000rpm 350ft-lbs @ 3000rpm 400ft-lbs @ 4000rpm 370ft-lbs @ 5000rpm 350ft-lbs @ 6000rpm 300ft-lbs @ 7000rpm Force at ground, With 12.3:1 total gear reduction 2460lbs of force 3321lbs of force 4305lbs of force 4920lbs of force 4551lbs of force 4305lbs of force 3690lbs of force Big Engine 200ft-lbs @ 570rpm 390 ft-lbs @ 1100rpm 480ft-lbs @ 1700rpm 470ft-lbs @ 2300rpm 410ft-lbs @ 2900rpm 360ft-lbs @ 3400rpm 328ft-lbs @ 4000rpm Force at ground, With 7.0:1 total gear reduction 1400 lbs of force 2730lbs of force 3360lbs of force 3290 lbs of force 2870lbs of force 2520lbs of force 2296lbs of force You can see how the gearing really helped out the smaller engine. Now the force you see shown in the chart, is what is actually causing the car to accelerate, that's the actual force coming in contact with the ground and pushing the car. Now if we average the lbs of force listed in the chart, the Big engine comes out at an average of 2638lbs (in first gear). But the well geared, higher HP, Small motor, shows a whopping average of 3936lbs. And the average output has a more direct effect on acceleration than just peaks numbers, which may only remain at that peak for a very short period. So now you can see how that smaller engine, with more HP, but less torque, can really lay down the smack on the bigger torquier engine. So in summary, Torque is twisting force (cause of acceleration), RPM is work rate (Allows Speed), and Horsepower is the culmination of both (Torque times the rate it is delivered). Have a nice day. Last edited by T88H34GSUPRA; 08-19-2003 at 08:00 PM..