General FAQ: Horsepower vs torque

[mrfunji]

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.