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Old 10-22-2010, 04:02 PM   #1
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Ok, so an online buddy and myself have been arguing non-stop over this **** for a couple days and cannot seem to come to a conclusion.

I turn to you ***** to settle this ****, and it BETTER be proven otherwise you're of no help.

He states: peak horsepower determines car's top speed.
I firmly believe that net torque plays a major role.
He states: regardless of whether one car has 800ft/lbs of torque MORE than the other car ALL OTHER VARIABLES BEING EQUAL (same weight, gearing, cd, etc) that while the higher torque car will REACH its top speed quicker, the lower torque car will still hit the SAME top speed: it would just take a lot more time. I believe that due to the low torque car not having enough torque to overcome resistance at high speeds it will hit a wall faster. He doesn't think that is the case.

Again, everything else being equal. And assuming gearing not being the limiting factor.

WHAT SAY YOU?

(and more importantly, please provide proof or a good explanation)


Thanx gays
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Old 10-22-2010, 04:10 PM   #2
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So if they have the same peak HP but one car has (let's say) twice the peak torque, the car with x1 torque must rev much higher than the car with x2 torque, right?
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Old 10-22-2010, 04:23 PM   #3
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I'd say HP. Bikes and F1 cars are torquiless wonders (considering) and they have very high top speeds. But then again, look at the Audi and Peugeot ALMS cars....all TQ and they haul ***.
They situation described is kinda dumb...since HP is a direct calculation of TQ....more TQ means more HP.

A more reasonable way is to think of it this way. You have two identical 2002 Camaro SS' sitting next to each other. They both make the same HP/TQ and both have the same gears . Try driving one in just the torque curve and the other in the horsepower curve. What do you think will happen? There is a reason you rev an engine past it's peak TQ...unless it's some giant displacement engine that can't handle higher revvs and gear must be accommodated to make use of the available torque (diesel?).
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Old 10-22-2010, 04:31 PM   #4
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Quote:
Originally Posted by mgeoffriau View Post
So if they have the same peak HP but one car has (let's say) twice the peak torque, the car with x1 torque must rev much higher than the car with x2 torque, right?
Yes. but in this case we're saying that EVERYTHING else besides torque is equal. meaning they'd both rev to the same amount of rpm, whatever that may be
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Old 10-22-2010, 04:43 PM   #5
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I have some theories. Subscribed for entering the discussion later.
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Old 10-22-2010, 04:44 PM   #6
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i can see his point. hp number tells you where the torque peak is.

a higher torque peak is fine (f1,bikes) because you can always gear it down. yer 300ftlb torque @ 3k is same as 150ftlb @ 6k after a 1:2 gearing change. so without knowing anything else about the car, i would guess the higher hp # will have higher top speed.

wind resistance is no joke: goes up by velocity^2. you will definitely be able to see any difference in torque to the wheels between the 2 cars as well as the coefficient of drag difference.

the coefficient of drag numbers you see in the automotive press also vary with the square. its funny, because it doesn't appear that many of the journalists understand that.

EDIT: there was a big 'ol argument on the m3 maillist back in the day when the s2k first came out. s2k has no torque, will be slow blah blah. then somebody ran the numbers and it turns out both cars made the same torque to the wheels (in 4th gear iirc). albeit with a 1.2 liter deficit and different gearing on the s2k side...

Last edited by jasonb; 10-22-2010 at 04:55 PM.
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Old 10-22-2010, 04:48 PM   #7
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I always thought horsepower made the MPH, Torque made the ET?

http://www.epi-eng.com/piston_engine...and_torque.htm
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Old 10-22-2010, 04:54 PM   #8
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so compare that to a car that has a peak 5hp higher but only at redline.
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Old 10-22-2010, 05:00 PM   #9
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if you're talking top speed, then only the power at that speed matters. and power and torque are proportional.

so you need to have the highest wheel RPM (road mph basically) and enough torque to push the car forward. all HP is is torque over time. or how fast you can deliver torque.

if both cars have exactly the same hp at the same maximum RPM, they will be the same speed. by definition, HP is torque x RPM / constants.

suggesting that the car with more torque at that RPM will be faster because it can "push harder" is meaningless because they have the same hp -- and therefore they must have the same torque.
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Old 10-22-2010, 05:00 PM   #10
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keep in mind guys that EVERYTHING besides torque output is the same. and we're assuming flat, linear torque curve. not one that falls off up top like on a turbodiesel or small turbo car.
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Old 10-22-2010, 05:03 PM   #11
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Quote:
Originally Posted by y8s View Post
if you're talking top speed, then only the power at that speed matters. and power and torque are proportional.

so you need to have the highest wheel RPM (road mph basically) and enough torque to push the car forward. all HP is is torque over time. or how fast you can deliver torque.

if both cars have exactly the same hp at the same maximum RPM, they will be the same speed. by definition, HP is torque x RPM / constants.

suggesting that the car with more torque at that RPM will be faster because it can "push harder" is meaningless because they have the same hp -- and therefore they must have the same torque.
so then the argument is absolutely useless?

neither one of us is completely right cause power and torque are linear?
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Old 10-22-2010, 05:08 PM   #12
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Quote:
Originally Posted by 18psi View Post
so then the argument is absolutely useless?

neither one of us is completely right cause power and torque are linear?
they're not linear, they're proportional. at any given RPM, there is a fixed relationship between torque and horsepower.
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Old 10-22-2010, 05:09 PM   #13
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Peak power. As long has you have enough power under the curve to reach your peak power band. It doesn't matter if you make 300ft lbs of torque at 3000 rpms, because what's more important is how much power you make at 5-7k rpms, the range you'll be in when attempting a top speed run. Yes, more power down low will get you to a top speed faster, but it won't be the same top speed.

We might as well just call it power in this scenario.


I remember seeing an acceleration simulator that allowed you to enter specific power curves. It would demonstrate this concept very well.
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Old 10-22-2010, 05:10 PM   #14
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horsepower area under the curve, for the powerband

edit: they have acceleration/shift point calculators... like someone else said it illustrates this perfectly. horsepower is power. PEAK horsepower doesnt really mean ****.

horsepower is top speed etc etc is just video game ****

Last edited by aaronc7; 10-22-2010 at 05:22 PM.
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Old 10-22-2010, 05:13 PM   #15
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the answer is 42.

it's always 42
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Old 10-22-2010, 05:24 PM   #16
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Quote:
Originally Posted by Bryce View Post


I remember seeing an acceleration simulator that allowed you to enter specific power curves. It would demonstrate this concept very well.
If you could post a link to it that would be fantastic
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Old 10-22-2010, 05:27 PM   #17
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forget area under the curve! the only thing that matters is how fast the wheels are turning.
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Old 10-22-2010, 05:28 PM   #18
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Found it. I just used the default graph and tailored the torque graph to my liking. www.vimulator.com is pretty cool.


Power under the curve:
Name:  Vimundercurvegraph.jpg
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Name:  Vimundercurve.jpg
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Peak power:
Name:  Vimpeakgraph.jpg
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Name:  VimPeak.jpg
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Peak power wins, but the power under the curve did get there about 20 seconds faster ( I waited to take the screen shot).

Peak power determines a car's top speed

You could give the power under the curve graph 400 ft lbs of torque under the curve, tapering to 200 by redline, and it would still never ever go as fast as 400 ftlbs at redline.

Last edited by Bryce; 10-22-2010 at 05:39 PM.
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Old 10-22-2010, 05:40 PM   #19
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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.
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Old 10-22-2010, 05:43 PM   #20
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I'm demonstrating that what your friend said is correct.

You should go edit the torque graphs on vimulator, take some screenshots, and show us what you're talking about then.
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