A
Anonymous
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The torque versus horsepower argument has been around for as long as there've been engines and continues to motivate and entertain gearheads to this day. Here's the question in another form: "Is torque or horsepower more important to acceleration and top speed?"
Answer: Yes! :roll:
As SM wrote in another thread, torque is a force, which can be directly measured. In fact, it is worth noting that nearly all dynos measure torque and then calculate horsepower using the following equation: Power=[torquexRPM]/5252. There may be a few dynos around that directly measure horsepower, but you and I will never strap our engines into them.
That's it then. Torque is the King. Long live the King. Now let's all go have a cold one.
But wait, you say! If torque is the end all and be all, then why do I keep hearing about the importance of horsepower? Simple, horsepower is what enables us to take advantage of gearing to multiply the effect of torque.
Let me illustrate with an example. My friend Dave has an '85 MR2 with the Toyota 4age engine making 112 hp at 6600 rpm and 97 lbs/ft at 4800 rpm, and has a redline of 7500 rpm. I have a Golf TDI making 90 hp at 3750 rpm and 155 lbs/ft at 1900 rpm with a redline of 4500 rpm. Each car has about 12:1 multiplication in 1st gear, but the TDI has only 2.5:1 in 5th while the Toyota has about 3.7:1.
From a dead stop it looks like the Golf is a sure winner, since it has 155x12=1860 lbs/ft of tire smoking torque. Meanwhile, Dave's MR2 is flailing like crazy trying to keep up with its mere 97x12=1164 lbs/ft at an ear-splitting 6600 rpm. Even with its 400 lbs lower weight (2450 vs 2850), Mr Two is well behind, since each foot pound of torque is trying to accelerate 2.1 lbs of car, while the Golf's torque is only moving 1.5 lbs.
So, I've jumped off to a quick lead in my race to top speed with Dave and am already starting to taste the beer he's going to buy as we row up through the gears. But then we get into 5th gear and something strange happens. My Golf is still making a peak torque of 155 lbs/ft, but that's only being multiplied by a miserable 2.5:1. Gulp...155x2.5=386 lbs/ft, versus Dave's 97x3.7=358 peak torque. Now the shoe is on the other foot, since Dave's lighter weight translates to a torque loading of 6.84 pounds, while the Golf is trying to accelerate 7.38 pounds per lb/ft available. "DANG!" I say as Dave goes zipping past with a big grin on his face. 8)
What went wrong? Simple, by revving to a higher rpm, Dave is able to multiply the torque he has available through steeper gears to achieve greater net acceleration and top speed. Even though Dave's torque available is lots lower than mine, he is ultimately able to out-run me.
Now let's examine another case -- my SCCA Formula Atlantic race car. When we started racing the car, the engine made 235 hp at 9100 rpm and 136 lbs/ft at 7600 rpm, redlining at 9800. [In the past I have incorrectly listed our torque as ~116, but I dug out the dyno sheets tonight.] We have continued to develop the engine over the years, and it now boasts 252 hp at 9600 rpm and ~140 lbs/ft at the same 7600 rpm, and can reliably rev to 10,500. From the equation above, we can see that it is delivering just 123 lbs/ft at redline (assuming 245 hp at 10,500).
So what does that mean? Well, at 7600 rpm the engine has about 1450 lbs/ft of torque-multiplied thrust available to accelerate a 1300 pound package through a pair of 15" wide rear meats. That's less than a pound of car per pound of available torque!
Furthermore, at 150 mph in 5th we only need to pull 14 mph per 1000 revs. That's only a little more than your road car pulls in 2nd gear. Even at redline in 5th gear with its 1.2:1 ratio and a 3.89 diff, we are multiplying the engine's 123 lbs/ft to 575 lbs/ft of torque. That's still less than 3 pounds of car for each pound of available torque.
Now you know why I like high revving engines.
PS - For those still reading, here are some numbers from a modern F1 car: 800 hp at 18,000 rpm. To solve for torque, use T=(HP*5252)/RPM. Assume 7th gear is about 6-7:1 total. Solve for available torque. Tire spin occurs at anything above about 1000 drive-wheel lbs/ft...
Answer: Yes! :roll:
As SM wrote in another thread, torque is a force, which can be directly measured. In fact, it is worth noting that nearly all dynos measure torque and then calculate horsepower using the following equation: Power=[torquexRPM]/5252. There may be a few dynos around that directly measure horsepower, but you and I will never strap our engines into them.
That's it then. Torque is the King. Long live the King. Now let's all go have a cold one.

But wait, you say! If torque is the end all and be all, then why do I keep hearing about the importance of horsepower? Simple, horsepower is what enables us to take advantage of gearing to multiply the effect of torque.
Let me illustrate with an example. My friend Dave has an '85 MR2 with the Toyota 4age engine making 112 hp at 6600 rpm and 97 lbs/ft at 4800 rpm, and has a redline of 7500 rpm. I have a Golf TDI making 90 hp at 3750 rpm and 155 lbs/ft at 1900 rpm with a redline of 4500 rpm. Each car has about 12:1 multiplication in 1st gear, but the TDI has only 2.5:1 in 5th while the Toyota has about 3.7:1.
From a dead stop it looks like the Golf is a sure winner, since it has 155x12=1860 lbs/ft of tire smoking torque. Meanwhile, Dave's MR2 is flailing like crazy trying to keep up with its mere 97x12=1164 lbs/ft at an ear-splitting 6600 rpm. Even with its 400 lbs lower weight (2450 vs 2850), Mr Two is well behind, since each foot pound of torque is trying to accelerate 2.1 lbs of car, while the Golf's torque is only moving 1.5 lbs.
So, I've jumped off to a quick lead in my race to top speed with Dave and am already starting to taste the beer he's going to buy as we row up through the gears. But then we get into 5th gear and something strange happens. My Golf is still making a peak torque of 155 lbs/ft, but that's only being multiplied by a miserable 2.5:1. Gulp...155x2.5=386 lbs/ft, versus Dave's 97x3.7=358 peak torque. Now the shoe is on the other foot, since Dave's lighter weight translates to a torque loading of 6.84 pounds, while the Golf is trying to accelerate 7.38 pounds per lb/ft available. "DANG!" I say as Dave goes zipping past with a big grin on his face. 8)
What went wrong? Simple, by revving to a higher rpm, Dave is able to multiply the torque he has available through steeper gears to achieve greater net acceleration and top speed. Even though Dave's torque available is lots lower than mine, he is ultimately able to out-run me.
Now let's examine another case -- my SCCA Formula Atlantic race car. When we started racing the car, the engine made 235 hp at 9100 rpm and 136 lbs/ft at 7600 rpm, redlining at 9800. [In the past I have incorrectly listed our torque as ~116, but I dug out the dyno sheets tonight.] We have continued to develop the engine over the years, and it now boasts 252 hp at 9600 rpm and ~140 lbs/ft at the same 7600 rpm, and can reliably rev to 10,500. From the equation above, we can see that it is delivering just 123 lbs/ft at redline (assuming 245 hp at 10,500).
So what does that mean? Well, at 7600 rpm the engine has about 1450 lbs/ft of torque-multiplied thrust available to accelerate a 1300 pound package through a pair of 15" wide rear meats. That's less than a pound of car per pound of available torque!

Furthermore, at 150 mph in 5th we only need to pull 14 mph per 1000 revs. That's only a little more than your road car pulls in 2nd gear. Even at redline in 5th gear with its 1.2:1 ratio and a 3.89 diff, we are multiplying the engine's 123 lbs/ft to 575 lbs/ft of torque. That's still less than 3 pounds of car for each pound of available torque.
Now you know why I like high revving engines.

PS - For those still reading, here are some numbers from a modern F1 car: 800 hp at 18,000 rpm. To solve for torque, use T=(HP*5252)/RPM. Assume 7th gear is about 6-7:1 total. Solve for available torque. Tire spin occurs at anything above about 1000 drive-wheel lbs/ft...
