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Old 05-23-2012, 12:52 AM   #11 (permalink)
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Torque by itself is meaningless.

A vehicle that has 300 ft-lbs of torque will always be quick... ish... but a vehicle that has 300 ft-lbs of torque at 2000 rpm is never going to be as quick past the first 30 km/h as one that makes 300 ft-lbs at 4000 rpm. Why? Because the car making 300 at 2000 is only making 114 hp, while the car making 300 at 4000 is making 228 hp... at 4000 rpm... and is most likely making 300 horsepower at 6000, whereas the car making 300 at 2000 is usually making 150-ish horsepower at 3500 rpm.

Torque is useful... but again, taking into account only peak torque or peak horsepower is very misleading.

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Old 05-23-2012, 10:49 AM   #12 (permalink)
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Power is 'how often/fast" the torque is produced.
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Old 05-23-2012, 01:04 PM   #13 (permalink)
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Torque down low in the rpm's is more useful and economical. A semi trailer truck is the perfect analogy of max torque benefit over the max hp rating.
Good info in your post niky.
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Old 05-23-2012, 02:15 PM   #14 (permalink)
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Quote:
Originally Posted by niky View Post
. . . a car accelerates faster at torque peak than horsepower peak
A car accelerates fastest (at any given road speed) with greatest torque at the wheels, which will be provided by putting it in a gear that puts the engine at peak horsepower. Do the math (or listen to a drag race).

Horsepower and torque are numerically equal at 5252 RPM.

Last edited by tortoise; 05-23-2012 at 02:20 PM..
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Old 05-24-2012, 06:35 AM   #15 (permalink)
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I don't disagree with you, but I didn't mean what you thought I meant. I simply meant that peak transient acceleration occurs at peak torque in the lowest gear a vehicle has, and acceleration tapers off past peak torque.

Yes, you keep it there because that gives you the best torque multiplication... except in the case of some diesels where torque tapers off greatly as they approach redline.

I have done the math. I even built a wheel torque calculator from scratch for use with video game programming. I had to brush up on my math to update it to take into account wheel sizes, since I can't tell a radian from a median. I had to do that because wheel size actually makes a sizeable difference in the results I'm publishing for an upcoming article given the low power output of the engines I was graphing.

Still working on graphing wheel torque against drivetrain drag, aero drag and rolling resistance, but the fudge factors are so big that classical equations given by the textbooks are almost useless without adding in a whole lot of correction factors...

Last edited by niky; 05-24-2012 at 06:43 AM..
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Old 05-24-2012, 10:05 AM   #16 (permalink)
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I would say that I don't know about start/stop systems but I do know about stop/start ones. ie I think that is how most manufacturers describe them.
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Old 05-24-2012, 02:15 PM   #17 (permalink)
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I have also heard it said that if you want better fuel economy you build your car for torque. But anyways unless you are planning on making all cars hybrids I think autostop is just going to add more needless complications to our cars. They are already too complicated the way it is.
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Old 05-24-2012, 02:41 PM   #18 (permalink)
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Quote:
Originally Posted by niky View Post
I don't disagree with you, but I didn't mean what you thought I meant. I simply meant that peak transient acceleration occurs at peak torque in the lowest gear a vehicle has, and acceleration tapers off past peak torque.
We are in full agreement. You can't shift down from first gear. Excuse me for misunderestimating you. The error I thought you made is not uncommon.
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Old 05-24-2012, 02:43 PM   #19 (permalink)
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Autostop doesn't actually add complexity to cars. Its just a little additional programming in the ECU, a beefier starter, and a beefier battery, thats it.
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Old 05-24-2012, 02:51 PM   #20 (permalink)
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Quote:
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Autostop doesn't actually add complexity to cars. Its just a little additional programming in the ECU, a beefier starter, and a beefier battery, thats it.
Do some start/stop systems use a starter/alternator, actually mechanically simplifying things?

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