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Old 19th April 2007, 20:09   #46
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ok... since its
All I can say is.... you idle a car.. at 4300rpm!... all the bhp or torque is unsued.... then why doesn't the RPM shoot up to the redline?... all torque is excess torque!
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Old 19th April 2007, 20:36   #47
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Quote:
All I can say is.... you idle a car.. at 4300rpm!... all the bhp or torque is unsued.... then why doesn't the RPM shoot up to the redline?... all torque is excess torque!
I really didn't get what you're trying to say here. Why idle at 4300 rpm?

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Old 19th April 2007, 20:59   #48
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Originally Posted by Shan2nu View Post
I really didn't get what you're trying to say here. Why idle at 4300 rpm?
Oh.. I meant revv.. a idling (parked in neutral) car... to that rpm.

but.. nevermind... lets leave that topic.

EDIT: let me take back my last post.... Howstuffworks "How Horsepower Works" explains.

Last edited by SLK : 19th April 2007 at 21:15.
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Old 19th April 2007, 21:04   #49
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About skipping gears, I too do that often on both an Ikon and a Swift, most commonly from 2nd to 4th at about 60. I do it mainly because 2nd gear is just so much fun after 30 but makes me feel a little guilty.

Ideally one should shift up through all the gears. I dont think its wise to stick to any guidelines such as shifting at particular speeds or rpm. It's more a matter of your feel of the car, and what you need the car to do immediately after you shift. For example, if you're on an uphill gradient and accelerating it would probably be best to hold 3rd till about 60 otherwise you'll be left behind.
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Old 19th April 2007, 22:34   #50
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Quote:
Oh.. I meant revv.. a idling (parked in neutral) car... to that rpm.

but.. nevermind... lets leave that topic.

EDIT: let me take back my last post.... Howstuffworks "How Horsepower Works" explains.
Fine, but what has gearing got to do with power? It's torque that is affected by the transmission.

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Old 19th April 2007, 23:48   #51
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Quote:
Originally Posted by Shan2nu View Post
Fine, but what has gearing got to do with power? It's torque that is affected by the transmission.
Shan2nu.. not again!.... we have had a similar discussion earlier... where we couldn't agree.
Torque is useless without rpm.... and torque and rpm read together mean power.
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Old 20th April 2007, 00:30   #52
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Torque is useless without rpm
No it's not. Torque is the measure of turning force applied. Whether you do it in 1min, 1hour or 1 year, the force remains the same.

When you apply torque to rotate something at a given rate, you get power.

A transmission does not affect power reaching the wheels.

Lets take the Vtec for EG:

At 6800rpm in 1st, the engine is producing 106hp and 81.869412lbft (110.52371nm) at the crank.

The transmission uses gear ratios to multiply the torque. 81.869412 * 3.23 (1st gear) * 4.058 (final drive) = 1073.0902lbft (1448.6718nm) at the wheels.

Therotically, even thought the torque has gone from 81.869412lbft from the crank to 1073.0902lbft at the wheel, the power should remain unchanged.

For this we first cal the rpm at which the wheel is turning. 6800 / 3.23 (1st gear) / 4.058 (final drive) = 518.7933rpm.

So now we've got :
Torque at the wheel = 1073.0902lbft
RPM of the wheel = 518.7933

So, horsepower = (torque * rpm) / 5252 = (1073.0902) * (518.7933) / 5252 = 106hp.

So you see, the transmission (1st gear) multiplied the torque by 13.10734 times.....but the power remained constant.

PS : My calculations donot include transmission/frictional losses.....so the actual readings at the wheel will be a bit lower.

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Old 20th April 2007, 01:36   #53
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Torque IS useless without rpm. Torque (lb ft) = 5252 x hp/rpm

If you have 0 rpm, your torque figure is meaningless. So you need rpm.
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Old 20th April 2007, 02:13   #54
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Quote:
Torque IS useless without rpm. Torque (lb ft) = 5252 x hp/rpm

If you have 0 rpm, your torque figure is meaningless. So you need rpm.
You don't need RPM as such, torque is only about the "R". When you cal revolutions for a given time, thats power.

Thats why power * rpm doesn't give you torque, it's the other way around.

Torque is the amount of work done, power is the rate at which that work is being done.

PS : Torque can be present even without any rotational movement "0 RPM"

Shan2nu

Last edited by Shan2nu : 20th April 2007 at 02:24.
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Old 20th April 2007, 02:38   #55
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Quote:
Originally Posted by Shan2nu View Post
PS : Torque can be present even without any rotational movement "0 RPM"
How?


..............
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Old 20th April 2007, 02:49   #56
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How?
General knowledge dude!!! Imagine you're trying to unscrew a bolt using a spanner.....but the bolt isn't budging as it's caught rust. The force applied by you * the length of the spanner gives you the torque that is being produced to turn the bolt. The bolt maynot be rotating, but the torque is being produced.

Torque is independant of time.....or movement for that matter.

Shan2nu

Last edited by Shan2nu : 20th April 2007 at 02:53.
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Old 20th April 2007, 02:54   #57
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Quote:
Originally Posted by v1p3r View Post
Torque IS useless without rpm. Torque (lb ft) = 5252 x hp/rpm

If you have 0 rpm, your torque figure is meaningless. So you need rpm.

Hey, I was wondering what you are trying to say when u say that torque is useless without rpm?? Useless in doing what???Throw some light pls.

Sorry, I just dont get what you and SLK are trying to say...!
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Old 20th April 2007, 02:59   #58
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Quote:
Originally Posted by ash7678 View Post
Hi Guys,
Have heard this a couple of times and thought that i might check it with everyone and have some technically correct insight too. Apparently to squeeze the most out of a litre it is best to upshift to the highest possible gear and go easy on the accelerator, even when the speedo drops below the 40kmph mark.
let me try and make it simple as possible
think of it like this..
- more throttle u give the more fuel you will burn.
- for mileage select the gear for which the least throttle is required.
now your queestion is how do I know which gear ?
select the gear which is appropriate to current load on the car, you should not select a high gear on a car when you see its not able to take the load.
You can feel if the car is not taking the load and may knock or shudder..
Experience will teach you to downshift before the car reaches a stage where it will knock or shudder.

just try to stick to mantain lowest RPM by mantaining lowest throttle but not forgetting that you are not loading the engine and making it knock/shudder etc etc.

Quote:
Originally Posted by ash7678 View Post
Is this true or is it better to stick to the frequent gear change style to maintain the tacho at 2.5k rpm?
these parameters change for diff conditions, 2.5 K may not be possible in some conditions... just dont be in a high gear if your car cannot handle, but be in the tallest gear with lowest rpm possible.
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Old 20th April 2007, 03:00   #59
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Originally Posted by Shan2nu View Post
Torque is independant of time.....or movement for that matter.
I'm sorry, but according to you, torque is work done.

Now, W = F s cos theta. And F = m a.

a is acceleration. As we all know, acceleration is a factor of both time and movement. Time since a = (v-u)/t, and movement, since if you have a finite value for a, some sort of displacement has occured.
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Old 20th April 2007, 03:19   #60
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V1p3r: Dude torque is the measure of a force's tendency to produce torsion and rotation about an axis, irrespective of howmuch rotation it is causing!!!

Pls realise that the Force vector is not measured by the resultantant work done/acceleration.

As shan2nu mentioned, torque is not measured by the amount of work its doing, its just the amount of work being done.

Last edited by The Wolf : 20th April 2007 at 03:20.
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