can someone briefly explain the difference between hp and torque for me?
02-22-2002, 05:18 AM
#11
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As long as they're short races
Torque monsters tend to have an advantage in a short drag race, but typically the car with a better power to weight ratio will win a quarter mile contest, as long as it's geared correctly. Anything longer than that, forget any torque advantage. Horsepower wins.
I completely agree that the area under the curve is critically important, but I'll also point out that, in your example of average torque over an rpm span, the engine that makes more average torque will also make more average horsepower.
I completely agree that the area under the curve is critically important, but I'll also point out that, in your example of average torque over an rpm span, the engine that makes more average torque will also make more average horsepower.
02-22-2002, 05:44 AM
#12
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Yep, more torque under the curve is more hp there, too.
If I remember correctly, Ford won LeMans in '67 or so with 427 "torque monsters".
Horsepower is, after all just torque times rpm (with a convenient factor to relate it). Obviously more torque at a given rpm = more hp there.
The point is we don't measure horsepower, we calculate it; similarly the vehicle only knows torque AND rpm...but that is power (work in a given time). Easy to get confused, huh? Even better, throw in 240 hp @ 8000 rpm (S2000) and you get to use more gear to multiply the torque to the wheels. But that's for another time.
Horsepower is, after all just torque times rpm (with a convenient factor to relate it). Obviously more torque at a given rpm = more hp there.
The point is we don't measure horsepower, we calculate it; similarly the vehicle only knows torque AND rpm...but that is power (work in a given time). Easy to get confused, huh? Even better, throw in 240 hp @ 8000 rpm (S2000) and you get to use more gear to multiply the torque to the wheels. But that's for another time.
02-22-2002, 06:05 AM
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You don't go 220+ down the Mulsanne straight on "torque"
Those Fords made a ton of horsepower.
But, coming back to your "area under the curve" argument, the GT40s could come off some of the LeMans corners a little harder than the Ferarris, due to their mid-range torque advantage.
But, coming back to your "area under the curve" argument, the GT40s could come off some of the LeMans corners a little harder than the Ferarris, due to their mid-range torque advantage.
02-22-2002, 01:12 PM
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Ford spun those 427's about 5400-5500 max.
So if 220 mph needed 550 hp, they were putting out 525 to 535 lb-ft @ 54-5500 rpm hp peak. To me that's pretty close to a torque monster.
If the Ferrari also had 550 hp, but was spinning 8000, it was producing 360 lb-ft at hp peak.
If the Ferrari also had 550 hp, but was spinning 8000, it was producing 360 lb-ft at hp peak.
02-22-2002, 01:43 PM
#16
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Nope. They twisted them a fair bit tighter than that...
That's why they went to cross-bolting the mains. "Side oiler" was the term.
If memory serves, you're pretty close on what those engines actually put out at the time, but they spun them to at least 6500 rpm - except when they were laying back with early shift points to avoid a dnf.
Whether they were "torque monsters" is a matter of interpretation, but they needed all of those thundering herds of horses to get over 220 mph. All the torque in the world won't help you if you're not making it at speed. (See the waterwheel anecdote in my post just below.)
If memory serves, you're pretty close on what those engines actually put out at the time, but they spun them to at least 6500 rpm - except when they were laying back with early shift points to avoid a dnf.
Whether they were "torque monsters" is a matter of interpretation, but they needed all of those thundering herds of horses to get over 220 mph. All the torque in the world won't help you if you're not making it at speed. (See the waterwheel anecdote in my post just below.)
02-23-2002, 10:52 AM
#17
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LOL. We were both a bit off the mark. See the link.
Max hp was at 5000.
Read that as "durability".
As a few posters here have said, power is torque times rpm; making torque at speed, right?<ul><li><a href="http://tucars.topcities.com/1965_gt40_mk4.htm.">http://tucars.topcities.com/1965_gt40_mk4.htm.</a</li></ul>
Read that as "durability".
As a few posters here have said, power is torque times rpm; making torque at speed, right?<ul><li><a href="http://tucars.topcities.com/1965_gt40_mk4.htm.">http://tucars.topcities.com/1965_gt40_mk4.htm.</a</li></ul>
02-23-2002, 11:18 AM
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HP and torque in Formula 1 and Winston Cup...some thoughts.
Here's an interesting comparison.
Let's say an 3.0 litre F1 engine makes 780 horsepower @ 17,500 rpm (probably a safe estimate), and a NASCAR Winston Cup 5.87 litre engine makes 780 horsepower @ 8750 rpm (probably also safe). Let's also say their rear tires are the same diameter, and turn 800 revolutions per mile (that's pretty close) and that both cars reach 187.5 mph @ power peak. That's probably close given the aerodynamics they run. Further, assume that the 187.5 mph is a drag limited speed; the horsepower required to push the car that fast exactly equals the horsepower available.
The rear tires are turning 2500 rpm @ 187.5 mph.
(The math: 60 mph = 1 mile/minute or 800 revs/minute for our tires. 187.5/60 x 800 = 2500)
Now let's assume 94.9% driveline efficiency for both cars (we could assume any efficiency). So .949 x 780hp = 740 hp to the rear wheels, OK?
Now, because HP =torque x rpm divided by 5252, we can rearrange the equation to solve for torque.
Torque = HP x 5252 divided by rpm. Agree?
Let's solve for torque at the rear wheels:
T = 740 x 5252/2500 or about 1555 lb-ft! How can this be? Remember that the engine is turning faster than the wheels, by the overall gear ratio.
For the F1 car that ratio is 17,500/2500 or 7.00:1, and for the Cup car 8750/2500 or 3.50:1.
Remember that gears multiply torque when they reduce speed, and vice-versa.
If we take the 1555 lb-ft divided by 7.00 we get 222 lb-ft at the F1 engine. Using HP= Torque x rpm/5252, we get about 740 hp. With the 94.9% efficiency backed out because we are at the flywheel, we get 740/.949 or 780 hp.
If we take the 1555 lb-ft divided by 3.50 we get 444 lb-ft at the Cup engine or about 740 hp which is 740/.949 or 780 at the flywheel.
The bottom line it the drive wheels don't care how the torque is produced, and by what. They only care that 1555 lb-ft is available at 2500 wheel rpm.
BTW, which of these engines produces more torque per litre at power peak? 222/3 = 74 lb-ft/L, and 444/5.87L = 75+. Torque per litre is a fairly good measure of efficiency. That suggests to me that the Winston Cup engine is just as efficient as the F1 engine at power peak.
Of course, the F1 engine makes 260 HP per litre, while the Cup engine makes only(!) 133 HP/litre; that's where the rpm factors in.
Now which of these cars would accelerate faster?
The 3500 lb Cup car or the 1400(?)lb. F1 car? Remember that acceleration = Force/mass and with only 40% of the Cup car's mass and the same force at the wheels, it's no contest: The F1 car by a factor of about 2+ times!
Comments?
Let's say an 3.0 litre F1 engine makes 780 horsepower @ 17,500 rpm (probably a safe estimate), and a NASCAR Winston Cup 5.87 litre engine makes 780 horsepower @ 8750 rpm (probably also safe). Let's also say their rear tires are the same diameter, and turn 800 revolutions per mile (that's pretty close) and that both cars reach 187.5 mph @ power peak. That's probably close given the aerodynamics they run. Further, assume that the 187.5 mph is a drag limited speed; the horsepower required to push the car that fast exactly equals the horsepower available.
The rear tires are turning 2500 rpm @ 187.5 mph.
(The math: 60 mph = 1 mile/minute or 800 revs/minute for our tires. 187.5/60 x 800 = 2500)
Now let's assume 94.9% driveline efficiency for both cars (we could assume any efficiency). So .949 x 780hp = 740 hp to the rear wheels, OK?
Now, because HP =torque x rpm divided by 5252, we can rearrange the equation to solve for torque.
Torque = HP x 5252 divided by rpm. Agree?
Let's solve for torque at the rear wheels:
T = 740 x 5252/2500 or about 1555 lb-ft! How can this be? Remember that the engine is turning faster than the wheels, by the overall gear ratio.
For the F1 car that ratio is 17,500/2500 or 7.00:1, and for the Cup car 8750/2500 or 3.50:1.
Remember that gears multiply torque when they reduce speed, and vice-versa.
If we take the 1555 lb-ft divided by 7.00 we get 222 lb-ft at the F1 engine. Using HP= Torque x rpm/5252, we get about 740 hp. With the 94.9% efficiency backed out because we are at the flywheel, we get 740/.949 or 780 hp.
If we take the 1555 lb-ft divided by 3.50 we get 444 lb-ft at the Cup engine or about 740 hp which is 740/.949 or 780 at the flywheel.
The bottom line it the drive wheels don't care how the torque is produced, and by what. They only care that 1555 lb-ft is available at 2500 wheel rpm.
BTW, which of these engines produces more torque per litre at power peak? 222/3 = 74 lb-ft/L, and 444/5.87L = 75+. Torque per litre is a fairly good measure of efficiency. That suggests to me that the Winston Cup engine is just as efficient as the F1 engine at power peak.
Of course, the F1 engine makes 260 HP per litre, while the Cup engine makes only(!) 133 HP/litre; that's where the rpm factors in.
Now which of these cars would accelerate faster?
The 3500 lb Cup car or the 1400(?)lb. F1 car? Remember that acceleration = Force/mass and with only 40% of the Cup car's mass and the same force at the wheels, it's no contest: The F1 car by a factor of about 2+ times!
Comments?
02-26-2002, 05:45 AM
#20
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Pretty much agree on everything
A couple of points:
First, in regard to your comment:
"The bottom line it the drive wheels don't care how the torque is produced, and by what. They only care that 1555 lb-ft is available at 2500 wheel rpm."
I definitely agree, and that leads to the point that horsepower is kind of an arithmetical shorthand. Once you "do the proofs", as you've done, it's clear that, no matter the torque, no matter the gearing, etc., it's horsepower that counts at any given car speed. I often make this point to debunk the persistent idea that changing to more aggressive final-drive gearing will give you an advantage at any speed compared to the stock gearing. It's true that more aggressive final-drive gearing may well offer an off-the-line advantage, but once past, say, 25 or 30 miles per hour, it's a tossup. After the aggressively-geared car shifts to second, the stock vehicle will have an advantage, until it has to shift to second, after which the modified car will have an advantage, and so on. Whichever vehicle is making the most horsepower at any given point will be accelerating harder, regardless of gearing.
The other point is that the Winston Cup cars are making maybe 60% of what your example shows in order to get to 187.5 mph. Without restrictors, they'd likely get to over 240 mph. Of course, this in no way affects your basic logic.
First, in regard to your comment:
"The bottom line it the drive wheels don't care how the torque is produced, and by what. They only care that 1555 lb-ft is available at 2500 wheel rpm."
I definitely agree, and that leads to the point that horsepower is kind of an arithmetical shorthand. Once you "do the proofs", as you've done, it's clear that, no matter the torque, no matter the gearing, etc., it's horsepower that counts at any given car speed. I often make this point to debunk the persistent idea that changing to more aggressive final-drive gearing will give you an advantage at any speed compared to the stock gearing. It's true that more aggressive final-drive gearing may well offer an off-the-line advantage, but once past, say, 25 or 30 miles per hour, it's a tossup. After the aggressively-geared car shifts to second, the stock vehicle will have an advantage, until it has to shift to second, after which the modified car will have an advantage, and so on. Whichever vehicle is making the most horsepower at any given point will be accelerating harder, regardless of gearing.
The other point is that the Winston Cup cars are making maybe 60% of what your example shows in order to get to 187.5 mph. Without restrictors, they'd likely get to over 240 mph. Of course, this in no way affects your basic logic.