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Old 10-22-2010, 05:43 PM   #21
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Quote:
Originally Posted by 18psi View Post
but that's the thing that I was saying (and y8s said it was impossible):

we're not talking UNDER THE CURVE. in this hypothetical instance the torque DOES NOT taper.
Then in that case, you are both right to an extent. The car with the most torque will win -> It will also have the highest horsepower.
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Old 10-22-2010, 06:15 PM   #22
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It's all torque and gearing.

Stop measuring in HP...it's derived (and proportional) to torque, as a function of angular velocity.

You can model this in MATLAB in 20min, or use the myriad online calculators.

For what it's worth the top speed on a Honda VFR increases with lower (numerically higher) gearing. Completely anecdotal, but a good example of how subtle changes in gearing can put the motor in a better part of the torque curves to overcome the aerodynamic forces on the vehicle.
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Old 10-22-2010, 06:22 PM   #23
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Originally Posted by gospeed81 View Post
For what it's worth the top speed on a Honda VFR increases with lower (numerically higher) gearing.
From a childhood spent reading Car & Driver, I seem to recall the occasional 6 speed that had top speed recorded in 5th gear as the 6th gear was very tall for the purpose of low-RPM interstate cruising/fuel mileage, and put the car too low in the power curve.
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Old 10-22-2010, 06:25 PM   #24
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Quote:
Originally Posted by mgeoffriau View Post
From a childhood spent reading Car & Driver, I seem to recall the occasional 6 speed that had top speed recorded in 5th gear as the 6th gear was very tall for the purpose of low-RPM interstate cruising/fuel mileage, and put the car too low in the power curve.
typical of a lsx + t56 setup, 6th is for the em pee gees
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Old 10-22-2010, 06:47 PM   #25
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HP

Air resistance increases by the square of the velocity. It takes more and more HP to increase your mph the faster you are going. Higher HP will win.

If you say we are ignoring wind resistance, then you are a ***, and I hate you
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Old 10-22-2010, 07:04 PM   #26
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I'm going to say HP. I've seen cars race that were same weight. One had the TQ and the other had the HP. TQ won in the beginning but HP always wins in the end. Just my .02
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Old 10-22-2010, 09:42 PM   #27
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horsepower wins

the engine determines the horsepower that reaches the wheels

the transmission determines the torque which reaches the wheels

and since transmissions dont actually produce power, torque is a completely useless number to base anything off of.

Lets assume that torque is a flat curve, as in a naturally aspirates or supercharged application.

Think of it this way, an engine that spins to 10k rpm and produces 50 horsepower will produce ten times more torque than an engine that spins to 100k rpm and produces 50 horsepower. Attach it to a transmission that slows the engine speed down by a factor of 10, and you have identical powertrains.

If you have an engine that spins to 10k rpm and produces 50 horsepower, and then you have another engine that spins to 20k rpm and produces 100 horsepower. Both produce exactly the same amount of torque if torque curves arew flat. If you attach a transmission to the 100hp engine that reduces engine speed by a factor of 2, the 100HP engine is still going to be producing 100HP, but now it will be doing it by producing twice as much torque as the 50hp engine instead of twice as many RPMs.

So, I will say it again, torque is a useless number in determining what an engine is capable of if the torque curve is anything near realistic, because torque is not determined by the engine, it is determined by the transmission, and transmissions do not produce power.
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Old 10-23-2010, 10:11 AM   #28
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Quote:
Originally Posted by fooger03 View Post
because torque is not determined by the engine, it is determined by the transmission, and transmissions do not produce power.
A transmission is only a speed reducer, or torque multiplier.

Please tell me where the torque is coming from if it's not coming from the engine...



The torque curve of a motor tells you EVERYTHING about the characteristics of the motor....where it produces the power you need, how to gear the car to use this power, etc.

Your post contradicts itself...but I'll try this one more time (or read y8s excellent post above).

Power is a function of torque and angular velocity. The ONLY thing that accelerates you down the road is the torque applied to the wheels. The speed of the motor at that road speed gives you a torque for the motor, multiplied by the speed reducers and then (usually) divided due to wheel radius. Once applied over a distance torque generates a FORCE...the force that must overcome all other forces on the car to continue accelerating it up to the top speed.


Now at speed you can call it power, because we now have rotational speed thrown in, but in force analysis you use torque to determine acceleration, and where acceleration stops (top speed).

Last edited by gospeed81; 10-23-2010 at 10:23 AM.
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Old 10-23-2010, 11:50 AM   #29
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I should also point out that if both cars are cruising at top speed--which is at redline (which we agree is equal because the cars are equal except for the torque curves), then they are both producing exactly the same torque and power at redline.

even if car A is maxed out at peak HP at redline
and car B is only at 10% throttle
there will never be a top speed disparity because the speed relationship is a fixed quantity.

Now... on some dynos one could show 10 times the power (and torque) at redline than the other because you can vary the load.

Which means your question should be "which car is faster towing a semi trailer?"
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Old 10-23-2010, 05:40 PM   #30
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I'm starting to see the light LOL
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Old 10-23-2010, 10:14 PM   #31
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Torque isn't a work function. Just sayin
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Old 10-23-2010, 10:54 PM   #32
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Pretend both cars are going 180MPH. Car one makes 2x the torque as car two. Since the gearing and the wheel diameter are the same, the RPM must be the same. Therefore car one also makes 2x the power and will easily go faster than car two.

The question you really asked is, "If two cars have the same drag, would one that puts more torque on the ground go faster than one that puts less torque on the ground?"

A: Yes.

Edit: Just realized post #9 says the same thing i just said.
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Old 10-23-2010, 11:00 PM   #33
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so then the argument is absolutely useless?
Utterly so.
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Old 10-24-2010, 08:35 PM   #34
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Originally Posted by GTRicky View Post
the answer is 42.

it's always 42
Yes...yes it is.



I have nothing to say that hasn't been said already...so thank you guys who said it already.
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Old 10-25-2010, 02:00 AM   #35
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This is basic physics. To go fast, the car must do work against air resistance, rolling resistance, internal friction..., so the more work the car can do per unit time the faster it can go. Power is definitionally work per unit time. The car that can do more work per unit time (more power) can go faster, provided it has proper gearing to allow it to use that power effectively.
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Old 10-25-2010, 02:07 AM   #36
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HP determines how fast your car will go. Torque determines how fast you will get there.

But then, there are million different variables that will affect both statements.
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Old 10-25-2010, 10:34 AM   #37
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Quote:
Originally Posted by gospeed81 View Post
A transmission is only a speed reducer, or torque multiplier.

Please tell me where the torque is coming from if it's not coming from the engine...
First off: I never once said that transmissions produce torque.

A transmission cannot change the amount of power that makes it to the wheels (with the exception of reducing power via. driveline loss) A transmission simply converts speed to torque.

Compare these two hypothetical engines:
Engine 1:
Flat torque curve - 100 ft-lb torque - 10k rpm redline = 190horsepower

Engine 2:
Flat torque curve - 100 ft-lb torque - 20k rpm redline = 380 horsepower

Now, lets put both of these engines into the same vehicle with a close-ratio transmission. (Not at the same time, 'cause that would be just silly)

Now, if we were in a perfect world, there would be no limit to how fast engines could spin, and yes: torque would rule all. Indeed, the only limiting factor on how fast our little cars could go would be how much torque they could put to the wheels to overcome the drag produced by wind resistance.

But our cars do indeed have rev limits. Speeds at which the engine will destroy itself if it travels any faster.

So, at top speed in 5th gear, our little cars have met their match vs. wind resistance at 8000 rpm. They are both putting out 100 ft-lb of torque and about 152 horsepower. There is some constant number "B" of torque applied to the wheels in both cars after the speed/torque conversion has been applied through the driveline. The same speed in 4th gear for this car requires the engine to spin at 11,500 rpm. The car with the lower revving engine cannot downshift. The car with the higher horsepower, higher revving engine can downshift, and does. It is now applying 1.43*B of torque to the drive wheels, and can accelerate to a speed faster than the lower power car.

So you see, the only thing that matters with regard to overcoming wind resistance to reach a higher speed is indeed the amount of torque you can apply to the drive wheels, unfortunately, torque provided to the drive wheels is not directly a function of torque produced by the engine, but instead is a function of torque output after the complete drivetrain. The two cars above produce the same amount of torque, but the higher horsepower car can make that torque at higher speeds.

The end result is: Given two similar cars, one with higher crank horsepower - the other with higher crank torque, and both with properly matched gearboxes: The higher horsepower car will outspeed the higher torque car every time.
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Old 10-25-2010, 01:44 PM   #38
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Quote:
Originally Posted by Jesus of Torque and Horsepower View Post
I should also point out that if both cars are cruising at top speed--which is at redline (which we agree is equal because the cars are equal except for the torque curves), then they are both producing exactly the same torque and power at redline.

even if car A is maxed out at peak HP at redline
and car B is only at 10% throttle
there will never be a top speed disparity because the speed relationship is a fixed quantity.

Now... on some dynos one could show 10 times the power (and torque) at redline than the other because you can vary the load.

Which means your question should be "which car is faster towing a semi trailer?"
omg this guy has it dead on!
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Old 10-25-2010, 01:51 PM   #39
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Get off your own nuts JOTAH.
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Old 10-25-2010, 03:06 PM   #40
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Quote:
Originally Posted by djp0623 View Post
Torque isn't a work function. Just sayin
Quote:
Originally Posted by fooger03 View Post
The higher horsepower car will outspeed the higher torque car every time.


I think we can agree that there are several ways to analyze this problem.

I was trying to demonstrate what I believe is the easiest method since steady state can be assumed at top speed.

Where I was wrong is in taking the tone that it is the only method, which it clearly is not.

There are lots of examples in this thread, and I can't go through all of them because actually getting a degree is more important to me today. A lot of them rely on assumptions or variables like equivalent gearing...therefore motor speed. I tried to account for this if you actually read my post...and am convinced that gearing is key, and variable, to take advantage of the power the two different motors will produce.

I'm only adamant about this because I had to write some code last week that optimizes gear ratios for max_speed given a torque curve and other forces on the vehicle (drag, incline, rolling resistance etc.).

Solve it however you wish, but don't discount the fact that my answer is still plausible (and received a 99 from the prof).
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