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horsepower vs. torque

Ok. So it's been debated and this is the real deal

What makes my car go fast? The difference between horsepowe and torque.
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Well start with some Physics 101:
An object remains at rest until acted on by an outside force.

In car terms, torque is the outside force. It is what actually moves the car. Horsepower is derived from torque, and is relative to time. In order to address these terms you need 3 things...force, work, and time.
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A Brief History:
The term "horsepower" was coined by Watt. He concluded that an average horse could lift a 550 pound weight 1 foot off the floor (now work is being done since the weight is moved). Also, Watt said it took this horse 1 second to move this 550 pound weight 1 foot off the floor. Therefore, this horse was doing work at a rate of 550 lb ft per second, or 33,000 lb-ft per minute, now determined to be one horsepower.
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A simple example:
Torque in an engine is a twisting force. Imagine a 1 cylinder engine with a rod and piston weight of 1 lb and a rod length of 1 foot. If we move this weight in a complete revolution, we do 2*Pi (6.28) ft. lbs of work (for simplicities case, this engine rotates in a circle). So what horsepower are we producing???

well, we use Watts numbers. 33,000/6.28 = 5254.

This means that if we spin our engine at 5254 RPM then we make one horsepower. At 2527 RPM we are making 1/2 a horsepower and so on.

On a dyno, you are measuring the torque produced by the engine and calculating the horsepower using the principles above.

torque * rpm = horsepower
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Welcome to carland

Torque is what makes your car accelerate. It is what you feel, you can't feel horsepower. While accelerating, your car will accellerate in any gear at a rate that maches your engines torque curve (less increases resistances at higher speeds). Your car accelerates hardest at the peak torque and accelerates less below or above that peak number. Making 200 ft-lbs of torque at 2000 rpm will accelerate at the same rate if you were making 200 ft-lbs of torque at 4000 rpm (in the same gear).

So at 2000 RPM your making: 200 ft-lbs * 2000 RPM / 5254 = 76 HP
At 4000 RPM your making 152 HP.

Now if you can pull at your peak torque for longer, you make more horsepower. Horsepower continutes to rise will after your peak torque is reached, and falls ones the torque curves decreases at a rate faster than the RPMs are increasing.
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The role of horsepower

Even though torque moves the car, horsepower plays a role in how fast it can accelerate. Horsepower is a measure of how long your engine is making torque

Now remember that gearing multiplies torque greatly. It is better to make more torque at high rpm than low rpm because you can take advantage of gearing.

Lets say your racing the F2T and the FE3, same torque numbers and same car weight and same gearing. The F2T would pull a head a little bit since it makes it's peak torque sooner, but the cars acceleratoin feels equal. However, because of the 6000 rpm redline, the F2T must shift into second gear, making less torque, while the FE3 rockets ahead because it has 1000 more RPMs left to make it's maximum torque in first gear (even if the peak torque fo the FE3 engine drops off at 6000 rpms, you still make more torque at 7000 RPMs in first gear than the F2T at max torque in second gear).
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So horsepower is how long your car can pull, and torque is how fast your car can get going.

At high speeds more horsepower is more essential because your car can pull for longer, taking advantage of gearing, and you can put down more torque at high RPMs.
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Closing thought:

How do you make the fastest car in GTA 3?

Use the F1 Car with the shortest gear ratio. Even though your top speed is about 100 miles an hour, you get there in the blink of an eye.
 

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The role of horsepower

Even though torque moves the car, horsepower plays a role in how fast it can accelerate. Horsepower is a measure of how long your engine is making torque

So horsepower is how long your car can pull, and torque is how fast your car can get going.
This is true however when cars and horsepower are mentioned beak horsepower is usually mentioned. Peak horsepower is often achieved at or near peak rpm and peak horsepower does not take into account the power-band curve before this point.

For example you have two motors. Motor A and Motor B
Motor A dyno's 399 hpr at 7000rpm putting down 299.4 ft-lbs torque at 7000rpm.
Motor B dyno's 400 hpr at 7000rpm putting down 300.1 ft-lbs torque at 7000rpm.
But motor A has better breathing head (s), better cam (s), variable valve timing or forced induction or ....
Motor a starts making a peak torque of 400ft-lbs at 3000 rpm and genates 398ft-lbs torque at 5252rpm and the torque slowly stats declining. So Motor A makes 398 hpr at 5252 rpm.
Motor B does not breath well at low RPM and starts making it's peak torque of 330ft-lbs at 5000rpm and caries it to 5252 then torque declines at a slower rate than Motor A to 7000rpm.
So Motor B makes 330 hpr at 5252 rpm.
Motor A's torque curve is declining faster from 5252rpm to 7000rpm than motor B's torque curve but Motor A is still putting down more torque for most of the 1748rpm above 5252rpm and put down lots more torque for a much longer time than motor B below 5252 rpm.

Obviously Motor A is faster throughout the entire rpm range.
But motor B makes 400hpr @ 7000rpm and Motor A only makes 399hpr @ 7000rpm.
Motor A made more torque for longer and at any given RPM point on the dyno is making more power, except at peak RPM.

Motor A and Motor B's owners both dyno'd on the same day, at the same shop, a few hours apart and where both given a dyno readout sheet.

Both owners looked at their sheets and memorized what they though to be most important, peak HPR at XXXX rpm.

The following week they are both at the same bar and meet for the first time, start talking about cars and while sitting on bar stools start the most pointless bar stool discussion about HPR and compare numbers, of course neither of them carry around their dyno sheets.
Motor B's owner says 400hpr @ 7000rpm and Motor A's owner replies damn you beat me by 1hpr. Motor B's owner wins the bar stool race and clearly he should because "Horsepower is a measure of how long your engine is making torque" wait no that can't be right, let me double check "Horsepower is how long your car can pull, and torque is how fast your car can get going" I keep reading it but it still doesn't make sense because dyno hpr numbers are only calculated one point in the rpm band at a time.

So how could the hpr # hold the significance of "Horsepower is a measure of how long your engine is making torque"
If we calculated the RPM from gear shit to gear shift or redline.
Lets say 3800 rpm to 7050rpm, the motor accelerates for 3250 rpm after 1st.
We take torque readings every 10 rpm, we add all 325 torque readings and divide it by 325 we have the average torque over the usable powerband.
To get an average HPR # over the usable powerband we could calculate the horsepower at each of the 325 rpm points add them up and divide by 325. Or simply multiply the average torque X by the average rpm, in this case 5425rpm.

Knowing average torque and average horsepower throughout the usable rpm range for every gear, vehicle top speed and vehicle weight would easily clarify which car accelerates faster and would win a race of X distance or to Xspeed.
Because torque curves and Hpr bands aren't linear simply having a vehicle peak toque and peak horsepower numbers at whatever rpm they make them at give very little information as to how the car performs before and between those points.


" Making 200 ft-lbs of torque at 2000 rpm will accelerate at the same rate if you were making 200 ft-lbs of torque at 4000 rpm (in the same gear)"
If this statement is true:
If two cars race the quarter mile, they have even weight and traction, they both have evenly matched gears for their rpm ranges (redline in the same gear happens at the same speed despite rpm) they both accelerate for 4000 rpm in every gear and put down exactly 200 ft-lbs torque at the wheels during the entire 4000rpm in every gear. Vehicle 1 launches at/accelerates from 2000 to 6000 rpm and vehicle 2 launches at/accelerates from 4000 to 8000 rpm.
Than both cars would run the same 1/4mile time and trap the same speed but vehicle 2 would make 25% more horsepower than vehicle 1 during it's entire 4000 rpm power band.

Looking at both these cars dyno sheets would also be deceptive, vehicle 2 horsepower curve would be the exact same shape and length as vehicle 1 but 25% higher and 25% farther right in the rpm band making vehicle B look much faster on paper until you simply overlap the two dyno sheets and line up the start of both torque curves and realize they are identical.

Horsepower can be a deceptive Iyar
 
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