The Difference Between Horsepower & Torque - How It Works

What’s the Difference Between Horsepower and Torque? The Answer Might Surprise You

Stephen Kim Jun 1, 2011 0 Comment(s)
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This example shows why you can have a big engine that makes much more torque than a smaller engine, but doesn’t produce any more horsepower. Torque is important, but it’s not nearly as important as the rpm at which that torque is produced. To illustrate the point, let’s compare a ’70 Buick 455 to a ’70 LS6 big-block Chevy. The Buick made 510 lb-ft of torque compared to the Chevy’s 500 lb-ft. If you thought that the Buick could outrun the Chevy because it made more torque, you were living in a dream world. Since the Chevy made peak torque at 3,600 rpm instead of 2,800 rpm, it made 450 hp compared to the Buick’s 350 hp. Torque is directly related to displacement, and in the last 40 years, torque output per cubic inch has only gone up 10 percent at most. On the other hand, horsepower per cubic inch has gone up dramatically, nearly 30 percent, in that time. That’s because today’s engines aren’t producing that much more torque, but they’re maintaining that torque at a much higher rpm before it drops off.

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Torque Rules

Jon Kaase: Horsepower is just a figure that’s calculated from math. When you put the gas pedal to the floorboard, torque is what you feel. In a street car, you want lots of torque. Let’s say you have a small-block V-8 that makes 250 hp at 5,500 rpm and a small Japanese V-6 that makes 250 hp at 7,000 rpm. If you drove both of them back to back, there would be no comparison on how much faster the V-8 would feel because the smaller motor makes far less torque. Having too much torque is like having too much money. You don’t want any less of it. You just have to learn how to manage your account better. If you’re making so much torque that your car is blowing off the tires, either get some bigger tires or manage the power more efficiently with better electronics.

Horsepower is King

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Judson Massingill: The 433ci LS small-block in our ’99 Camaro drag car makes 1,050 hp naturally aspirated, and has an 8,000- to 9,600-rpm powerband. We don’t even know what the peak torque output is because the motor never turns that low rpm. The reason I quit paying attention to peak torque in race motors is because the vast majority of them operate at rpm that are above peak torque the entire run, whether it’s in NHRA Pro Stock or circle track. If peak torque was more important than peak power, we’d be better off putting our turbo diesel in our race car instead of in our tow rig since it makes more torque than our race engine. If torque is all that matters, why not put some taller gears in our Camaro so the rpm drops down to 7,000 rpm between shifts instead of 8,000? Our 433 small-block might make more torque at 7,000 rpm than at 8,000, but it makes far less power at 7,000 so the car would fall on its face and slow way down. Gearing multiplies torque, and turning more rpm enables you to run shorter gears. In many road racing and circle track applications, a high-rpm motor with lots of gear will make more torque at the rear wheels than a low-rpm motor with less gear since they’ll be turning more rpm and getting more torque multiplication coming off of a corner.

From our racing experience, it’s our opinion that the minimum rpm at which you can go wide-open throttle without breaking the tires loose is the most important part of the power curve. With our Camaro, that point happens to be right around 8,000 rpm. In some respects, the horsepower it makes at 8,000 rpm is more important than peak horsepower. That’s because if the engine speed drops down to 8,000 between shifts, the motor better have some beans at that rpm to keep the car moving down the track. At the end of the day, I am a “bottom end” kind of guy. I just refer to it as horsepower instead of torque.

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