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Old 10-23-2001, 05:33 PM   #1
jclick
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Default torque vs HP

Does anyone know a good resource to explain the difference between the two? Maybe something on the web.

Thanks
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Old 10-23-2001, 05:44 PM   #2
cRayZee
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2007 Legacy Spec B

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www.howstuffworks.com


hmm..difference of the two...

this is the part that confuses people and why they think they're different, but actually they're a function of the other.
lil shady about this: hp is the power needed to move something a certain distance or somethin like that, double check in that webpage i gave you

torque is the rotational force you applied. example: if you have a 1-ft lever and you apply 1 lb of force on one end, you've just applied 1 ft-lb of torque onto it. The longer the lever, the force you've applied gets multiplied. So, if you have a 5-ft lever, and apply 1 lb of force, you'd have 5 ft-lbs of torque, in exchange of that, you'd have to apply the force a longer distance. That's why people use breaker bars when they can't loosen a bolt or something.

Torque = R x F (R = radius of lever from pivot point to point force applied and F = force applied)

Their relationship:
HP = torque(rpm)/5252

So, horsepower is a function of the torque at a certain RPM divided by 5252.

5252 is this special number where the torque and hp curves intersect. Below 5252, the torque numbers are greater than the hp numbers.

Good way to look at it is by checking out hp and torque curves. According to that equation, the ideal situation would be if torque never decreased as you hit the higher revs (As the engine revs higher, each stroke can't produce as much power cuz it can't breathe as well). This is when you see a drop on the torque curve when it hits the higher revs. When this happens your hp curve flattens @ the same range. (You might be losing torque @ the higher revs, but you're revving so high, that the engine's constantly pushing the car faster than @ lower rpms ) i don't know if that made sense...

here's something similar:
if you were pushing someone on a swing. For low speeds, let's say you're pushing the swing every 3 or 4 swings only. If you want them to go faster, you push more often.

So...this is how V-tec does its magic. @ higher revs, it allows the engine to breathe, keeping most of its torque, and by allowing it to rev higher than most other engines, it can output a lot of horsepower, even with their little torque.

imagine how much horsepower the RS could push if we could maintain our 166 ft-lbs of torque up to 6k?

166(6000/5252) = 189HP! mmmm


wish that helped

Last edited by cRayZee; 10-23-2001 at 06:13 PM.
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Old 10-23-2001, 06:03 PM   #3
Stanley
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Simply put, torque is to pull as horsepower is to acceleration.
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Old 10-23-2001, 06:17 PM   #4
Jim Lewandowski
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Think of HP as the resonant/natural frequency of the ability of the engine to breathe. IOW, based on A/F ratio and air dynamics/flow, a given engine produces more HP at a specific range/rpm.

Torque is usually looked at from a curve standpoint whereas HP is looked at mostly from a single RPM instance. For example, higher-end cars are usually geared such that in the highest (or 2nd to highest) gear, they are running very, very close to the peak HP RPM.

Conversely, torque is thought of as a curve wherein how an engine operates with respect to speed/RPM in each gear.

Since someone pointed out that HP IS a direct derivative of torque, they are related.

For instance, single (SOHC) engines usually have good overall torque (curve is somewhat flat) but not a lot of higher RPM torque/HP because they don't breathe/operate as well as DOHC (in our WRX case).

JL
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Old 10-23-2001, 06:22 PM   #5
cRayZee
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we can help it breathe by pushing more air in there! turbo, baby!
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