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Old 02-11-2009, 10:02 AM   #1
ZeeTwentyFour
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How do we factor torque?

Almost everyone uses pound per horsepower ratio's, or want to know how much horsepower a car makes, but that is only half of the story. What I want to know is how do we factor how much torque an engine makes into the performance of car? I always figured torque was more of a low-end off the line kind of thing, where as horsepower was a top-end kind of power. Am I right or wrong?

-James
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Old 02-11-2009, 11:44 AM   #2
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Since HP is a function of torque we essentually have a fairly precise representation right there. although, if you want to get a more accurate figure things get messy. first off you cant get accurate results without having the torque curve right infront of you. with that you need to write an equation that matches the trends of that curve. after you figure that equation you would have to apply calculus and integrate the curve over the rpm range you would be useing. aka if you were launching at 3000 rpms and taking it up to a 6000 rpm redline you would set your integration limits at 3000-6000. this would give you the net amount of force for a proper comparison. of course if you dont want to calculate that you could always just take torque figures every 250 rpms or so (more or less depending on how accurate you want to be) and add those all together, that would give you an ~net torque value that could be used to calculate. either way to properly factor you would need the entire torque curve
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Old 02-11-2009, 03:17 PM   #3
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Torque is kinda' like the amount of work that can be done while horsepower is more like how fast the work can be done. I'm sure you can find the actual equation for torque and horsepower but that doesn't look like what you're asking. Torque can be made at low RPMs (like locomotive engines - max' RPMs on some are like 1050 [http://www.getransportation.com/na/en/locofacts.html]) but you can change the torque curve by manipulating many other components on the engine, like camshafts, heads, etc. If you are wondering if torque will make a performance car better, I don't know if there's a good answer to that. I mean, diesels are known for making torque, but most of the time be low on power. However, people like Gale Banks are investing heavily in diesel power and are making tremendous torque and horsepower. If you're looking to see which you want more, torque or horsepower, you'll probably find it depends on the disipline you're working under. Torque will kick you off the line in drag racing, however, by mid-track, if you don't have horsepower, you'll stop accelerating. However, if you don't have torque, you're going to come off the line soft, get a low ET, but trap a relatively high MPH because by the time your at the end of the track, horsepower is accelerating you, not torque.

It's my understanding you want a good balance, either way. Without torque, accelerating from slower speeds is going to hurt you some, but you'll have a good top speed. Without power, you'll be able to squirt out of corners really well, but be limited on the straights.

I know there are many here who can elaborate on this a lot better and probably more accurately.
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Old 02-12-2009, 01:03 AM   #4
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Two words: Average Horsepower!

Sure, a Ferrari 430 makes 450+ HP, but that horsepower is in a narrow range of RPMS, from about 7000-8000RPM. Which makes the average HP low, but if you can keep the motor in that narrow range, it will MOVE!

The LS3 on the other hand makes a LOT more HP down low in the RPMs (because of the high amount of torque available down there, HP~torque x RPM), yet is able to carry that power all the way to redline, which gives it more average HP and that feeling of quick acceleration.
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Old 02-12-2009, 01:39 AM   #5
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Quote:
Originally Posted by ZeeTwentyFour View Post
Almost everyone uses pound per horsepower ratio's, or want to know how much horsepower a car makes, but that is only half of the story. What I want to know is how do we factor how much torque an engine makes into the performance of car? I always figured torque was more of a low-end off the line kind of thing, where as horsepower was a top-end kind of power. Am I right or wrong?

-James
Low end torque = low end power. Actually, anywhere where you have torque you have power since

hp = torque*rpm/5252

horse power is what ultimately determines your acceleration but torque is important in determining when you will get that acceleration. I've created 2 dyno sheets with numbers that I essentially made up. They both make over 450 hp. One is for a torquey engine the other for a 'peaky' engine that makes a few more hp around 6000+ rpm. These engines roughly approximate what a small european V8 would be like compared to say a old 454 big block (though neither chart is based on much more that what I think is a good torque number at a particular RPM)

Its established that both make nearly the same peak power. However, lets take a look at how they behave at lower RPM's. The torquey one is is producing 200 hp at about 2100 rpm, but the other needs to be up to 3600 to make the same power because its only making 100 hp or so at 2100 rpm. This is the advantage of low end torque: more 'area under the curve'
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