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Location:
Land of Oz
Registered:
June 2004
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Torque & Horsepower & Acceleration
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Thu, 15 July 2004 07:46
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Hi,
I've been watching an argument going on regarding torque and horsepower, in relation to acceleration.
One dude says its the torque that provides the acceleration and the turning power to the wheels and that's what does the work. The other dude says it's the horsepower that does the work and it's horsepower that gives the acceleration.
I've asked it before, and I'll ask it again... someone illuminate me on this?
seeyuzz
river
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Location:
Brisbane
Registered:
June 2003
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Location:
Brisbane
Registered:
May 2004
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Re: Torque & Horsepower & Acceleration
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Thu, 15 July 2004 08:13
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i thought that torque controlls the hp...like if u have hardly any torque and 1000hp, you wont get to use the 1000hp...but if u have 1000nm torque n hardly any hp then you would use all that really quickly...
so its combination of both, but if 2 cars weigh the same, have the same hp but different torque, the one with higher torque will win...
if the hp is the only difference, i think the one with more hp will have greater top-end power..
nb - I THINK!
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Location:
Land of Oz
Registered:
June 2004
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Re: Torque & Horsepower & Acceleration
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Thu, 15 July 2004 08:18
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Hi,
Okay. But a small tractor has massive torque and little horsepower, yet it couldn't out accelerate a normal car, even though it has more torque.
I'm trying to get my head around this one. Trying to figure the relationship.
seeyuzz
river
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Location:
Perth
Registered:
October 2003
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Re: Torque & Horsepower & Acceleration
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Thu, 15 July 2004 08:57
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Once again:
Torque = (Power x 60)/(2Pi x RPM)
Basically your car will accelerate faster the more power it has over a larger rev range.
What fro-daddy says is not really correct either. Youll probably find the car with the most area under it's power graph will win the acceleration race, even if it has slightly less torque.
A small tractor will not out accelerate a car cause it's only geared to do say 30-40km/h, not 180km/h, simple really.
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Location:
Lost in the K hole
Registered:
May 2002
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Re: Torque & Horsepower & Acceleration
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Thu, 15 July 2004 09:05
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in simple terms:
torque is required to accelerate a rotating object (ie wheel)
the more torque you have, the faster it will accelerate.
horsepower is a term used to describe the ability of torque to continue accelerating a rotating object at higher and higher rpms.
ie - a powerful engine wih massif horsepower is due to its engine continuing to produce large torque even at high rpms.
so, in answer, torque accelerates a car - whether that be from standstill, or whilst roling. the more torque, the faster it will accelerate. the ability for a car to continue accelerating when already going fast requires yet more torque, and this is generally referred to as horsepower.
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Location:
Brisbane, QLD
Registered:
February 2003
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Re: Torque & Horsepower & Acceleration
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Thu, 15 July 2004 09:12
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| ed_ma61 wrote on Thu, 15 July 2004 19:05 |
in simple terms:
torque is required to accelerate a rotating object (ie wheel)
the more torque you have, the faster it will accelerate.
horsepower is a term used to describe the ability of torque to continue accelerating a rotating object at higher and higher rpms.
ie - a powerful engine wih massif horsepower is due to its engine continuing to produce large torque even at high rpms.
so, in answer, torque accelerates a car - whether that be from standstill, or whilst roling. the more torque, the faster it will accelerate. the ability for a car to continue accelerating when already going fast requires yet more torque, and this is generally referred to as horsepower.
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i like that answer the best
and as i try interpret it
with the tractor, lots of torque...feck all hp
soooo it has the ability to accelerate fast...but not for long because of crap gearing?
or have i gotten myself confused?
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Location:
Lost in the K hole
Registered:
May 2002
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Re: Torque & Horsepower & Acceleration
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Thu, 15 July 2004 09:15
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forget gearing - think of only the engine
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Location:
Melbourne
Registered:
June 2004
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Re: Torque & Horsepower & Acceleration
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Thu, 15 July 2004 11:17
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Power = Torque x R.P.M.
The governing factor in acceleration is the torque available AT THE WHEELS. A torquey engine that won't rev needs tall gears, and as gearing gets taller (to give more speed) the torque at the wheels is reduced linearly. Conversley, a rev-happy motor that makes little torque can drive quite short gears, which don't reduce the torque available at the wheels as much.
So there ya go - a torque-monster that won't rev loses it's legs once the speed builds and it's gotta push a tall gear.
Also, a short-stroke screamer relies on short, close gearing to keep it revving, and multiply it's meagre torque.
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Location:
Potts Point, Sydney
Registered:
October 2003
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Re: Torque & Horsepower & Acceleration
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Thu, 15 July 2004 13:30
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| ed_ma61 wrote on Thu, 15 July 2004 19:05 |
in simple terms:
torque is required to accelerate a rotating object (ie wheel)
the more torque you have, the faster it will accelerate.
horsepower is a term used to describe the ability of torque to continue accelerating a rotating object at higher and higher rpms.
ie - a powerful engine wih massif horsepower is due to its engine continuing to produce large torque even at high rpms.
so, in answer, torque accelerates a car - whether that be from standstill, or whilst roling. the more torque, the faster it will accelerate. the ability for a car to continue accelerating when already going fast requires yet more torque, and this is generally referred to as horsepower.
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Thanx ed, thats a pretty sweet ass answer 
[Updated on: Thu, 15 July 2004 13:30]
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Location:
On your mum!
Registered:
May 2002
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Re: Torque & Horsepower & Acceleration
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Thu, 15 July 2004 14:06
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Ed's answer is good.
Skip's answer is technically correct.
YelloRolla's answer is something like this. Torque is the force required to turn something (crank, gears wheels etc) - horespower is derived from the torque at a specific RPM.
So following the formula Torque x RPM/5251 = HP.
A motor that makes lot's of torque at low RPM (IE Cummins diesel with 420HP at 2600rpm) is also making a shitload of power at the same RPM. Transposing that formula we can work out that it is making about 850ft/lbs of torque (at 2600RPM and it would have made more at a lower RPM).
A 1600cc 4A GTE making the same 420HP @ 8500rpm will need 260ft/lbs (at 8500RPM).
HP refers to rate of work and trying to separate it from torque in the context of engine output is just not possible (Like trying to talk about the speed of a vehicle and then trying to separate the kilometers from the hours - it is futile).
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Location:
Melbourne
Registered:
November 2003
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Re: Torque & Horsepower & Acceleration
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Thu, 15 July 2004 14:42
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As has been stated, torque * RPM = Power.
Torque at the wheels can be changed by different gear ratios. Power at the wheels cannot be changed by different gear ratios.
So technically, you want as much power as you can get, and just fit the right gears and diff to it to make up for torque.
Generally, when talking about drag races, V8s big strokers do a pretty good job 'cuz they hit torque very low in the rev range so it's easy to launch them. Though once it hits it's Torque peak, the torque curve drops off. This means that even though the power is going up through the rev range, it's not gaining as well as it could. So once a V8 (and I'm talking the big strokers here, not 4.0 or less ltr V8s) has launched it just gets all kinds of wrong and you are wasting a lot of displacement to make not so great power.
On the flip side a Honda VTEC engine hits max torque way up in the heady regions of RPM. This means it can't get off the line as quickly without a really clever launch. It does however mean that as the RPMS get higher, so does the torque so the power gains get quicker and quicker the higher you go. By keeping the torque up higher in the rev range, short stroker engines can get much better power / displacement ratios. Short strokers also make for better track race engines IMHO as their power up high is better (even if there is less of it than a big stroker V8).
Or so I have been told. Correct me if I'm wrong those of you who are more knowledgeable than I.
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Location:
Perth
Registered:
October 2003
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Re: Torque & Horsepower & Acceleration
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Thu, 15 July 2004 23:30
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| Quote: |
IE Cummins diesel with 420HP at 2600rpm
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That wouldnt be a 6CTA8.3 by any chance would it?
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Location:
Adelaide
Registered:
June 2002
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Location:
Adelaide, SA
Registered:
May 2002
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Location:
Perth
Registered:
October 2003
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Re: Torque & Horsepower & Acceleration
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Fri, 16 July 2004 04:49
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Proper engineers shouldnt have enough time to be surfing the web during work hours 
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Location:
Seattle area, USA
Registered:
June 2002
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Re: Torque & Horsepower & Acceleration
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Fri, 16 July 2004 08:10
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heres one for ya...
drive along in 2nd gear at the peak HP@rpm for your engine and floor it..
take note of what happens..
then drive along in 2nd gear at or just below your peak torque @rpm..
i'm sure you'll figure it out..
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Location:
Perth
Registered:
October 2003
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Re: Torque & Horsepower & Acceleration
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Fri, 16 July 2004 08:41
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| Quote: |
drive along in 2nd gear at the peak HP@rpm for your engine and floor it..
take note of what happens..
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The neighbours start throwing rocks at your car?
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Location:
toowoomba qld
Registered:
March 2004
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Re: Torque & Horsepower & Acceleration
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Fri, 16 July 2004 08:53
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| Skip wrote on Fri, 16 July 2004 18:41 |
| Quote: |
drive along in 2nd gear at the peak HP@rpm for your engine and floor it..
take note of what happens..
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The neighbours start throwing rocks at your car?
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Location:
toowoomba qld
Registered:
March 2004
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Re: Torque & Horsepower & Acceleration
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Fri, 16 July 2004 08:57
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| wil8115 wrote on Fri, 16 July 2004 18:10 |
heres one for ya...
drive along in 2nd gear at the peak HP@rpm for your engine and floor it..
take note of what happens..
then drive along in 2nd gear at or just below your peak torque @rpm..
i'm sure you'll figure it out..
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very true.
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Location:
Seattle area, USA
Registered:
June 2002
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Re: Torque & Horsepower & Acceleration
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Fri, 16 July 2004 09:15
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LOL.. well maybe, tough 'hood?
but you understand the point i was trying to make.
| Skip wrote on Fri, 16 July 2004 01:41 |
The neighbours start throwing rocks at your car?
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Location:
Melbourne
Registered:
June 2004
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Re: Torque & Horsepower & Acceleration
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Sat, 17 July 2004 05:24
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At their peak h.p, an F1 engine puts out around 870hp, at 18700rpm
right? Right.
power / rpm = torque
that gives 465Nm of torque at peak rpm. which is 155Nm/Litre
This compares to a M3's 114Nm/Litre.
Then again the M3's super-six should go for about 450,000km without a rebuild, whereas the F1 engine struggles to get past 450km. hmmmm..
no point. That's just the torque/h.p. thing in action. There's plenty-more torquey engines around (Porsche GT2 makes 172Nm/L) but none that Rev like that.
The Porsche makes 460hp from it's 3.6L Turbo at 6800rpm, btw.
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