Kg/m To Nm Torque

[Flux_nz]

Hey guys,

I recently had a dyno done, and the print off states a Kg/m reading instead of Nm.

It has 165.9 Kg/m

So after some research found this equation for a calulation for it:

Kilograms meters (Kg m) × 9.804 = Newton meters (Nm)

(reference)

So i chuck it in a calculator :

1617.66 Nm torque...

That seems WAY too high... (rb20det)

What am i doing wrong?

[Mandingo]

Sounds like you are converting the tractive effort, not the actual torque figure.

[Chrispy]

That conversion factor is correct for going between Kg.M and N.m.

But as Flipmo said it does sound like tractive effort, and that is another kettle of fish.

[Flux_nz]

So is there anything to take home from it?

Is it just a number that means nothing or does it explain something of my mods?

[Sarumatix]

This is my understanding,

Tractive effort is the amount of force the vehicle can exert (the amount it can pull).

Generally it is referred as either continuous or maximum i'm guessing you have maximum there which would simply be the highest reading seen while on the dyno.. which is typical at the lowest revs.

So it isn't really a measure of the engine so much as a measure of the ability of the entire car.

http://en.wikipedia.org/wiki/Tractive_force

[djr81]

  Flux_nz said:

Hey guys,

I recently had a dyno done, and the print off states a Kg/m reading instead of Nm.

It has 165.9 Kg/m

So after some research found this equation for a calulation for it:

Kilograms meters (Kg m) × 9.804 = Newton meters (Nm)

(reference)

So i chuck it in a calculator :

1617.66 Nm torque...

That seems WAY too high... (rb20det)

What am i doing wrong?

If you want the torque output of the motor it is easy.

Divide the powah output by the engine speed.

Powah measured in Watts (Watts equals kW times 1000)

Engine speed measured in radians per second (Which equals rpm times 2 times pi divided by 60).

That will give you the number in Newton metres.

9.81 Newtons is the force exerted by one kg of mass under the influence of gravity.

So there is your year 10 science lecture for the day.

Tractive effort can be best understood as the end result of the engine torque after it has found its way through the gearbox/diff/tyres. It will be at is highest at peak engine torque in the lowest available gear.

Edited December 10, 2009 by djr81

[pixel8r]

  djr81 said:

If you want the torque output of the motor it is easy.

Divide the powah output by the engine speed.

Powah measured in Watts (Watts equals kW times 1000)

Engine speed measured in radians per second (Which equals rpm times 2 times pi divided by 60).

That will give you the number in Newton metres.

9.81 Newtons is the force exerted by one kg of mass under the influence of gravity.

So there is your year 10 science lecture for the day.

Tractive effort can be best understood as the end result of the engine torque after it has found its way through the gearbox/diff/tyres. It will be at is highest at peak engine torque in the lowest available gear.

How does that work? there are cars with much less power than mine that get more torque at a lower engine speed...

also, it doesn't really work on turbo cars because torque output reaches its maximum long before the engine reaches max power output - after reaching max torque, the torque output actually decreases as both power and engine rpm increase...

maybe i'm reading it wrong? torque would need to factor in (overall/effective) engine displacement and also the energy contained per qty of fuel used etc.

[djr81]

  pixel8r said:

How does that work? there are cars with much less power than mine that get more torque at a lower engine speed...

Yes there doubtless are.

Eg

Motor 1 puts out 500Nm at 3000rpm.

Motor 2 puts out 250Nm at 6000rpm.

They both have the same power outputs - just that motor 2 is spinning twice as hard to produce that power.

  pixel8r said:

also, it doesn't really work on turbo cars because torque output reaches its maximum long before the engine reaches max power output - after reaching max torque, the torque output actually decreases as both power and engine rpm increase...

Yes it does work. Torque can be falling as power output is still rising. Motors never make their maximum power at the same revs as the maximum torque. That is why you see two figures quoted in car brochures, for example.

  pixel8r said:

maybe i'm reading it wrong? torque would need to factor in (overall/effective) engine displacement and also the energy contained per qty of fuel used etc.

Yes you are reading it wrong.

[mad082]

while talking torque and engines making less power but more torque, just look at tractors, etc. they will make thousands of nm's of torque at only a few hundred rpm, but they will only make the same sort of power of a small car.

as for the dyno, when i have had my cars on the dyno the torque reading has usually been in newtons, not newton metres.

[pixel8r]

  djr81 said:

Yes there doubtless are.

Eg

Motor 1 puts out 500Nm at 3000rpm.

Motor 2 puts out 250Nm at 6000rpm.

They both have the same power outputs - just that motor 2 is spinning twice as hard to produce that power.

sorry - I was incorrectly interpreting the formula...

torque = power / revs

So basically this is why on a dyno graph, the power curve will be steeper up until max torque, at which point it starts to flatten out.

I was getting confused thinking that the torque curve of a turbo car is very different to a non-turbo car...(but was forgetting the power curve is also different and corresponds to the torque curve) and also that the power/torque characteristics of petrol cars is very different to diesel cars...then when I used your formula I must've typed something wrong...

But I got it now.

Disappointingly, my stagea reaches 407N-m at just 3200rpm but by the time it hits 6400rpm (peak power) the torque will have dropped back to just 307N-m or thereabouts. Of course this is assuming the 206kw is correct at 6400rpm...(which it most likely isn't).

  Quote

Yes it does work. Torque can be falling as power output is still rising. Motors never make their maximum power at the same revs as the maximum torque. That is why you see two figures quoted in car brochures, for example.

I realise this. Just got confused trying to translate that into the formulas. I got stuck thinking how can torque go down if both power and revs are going up? Then I realised that obviously power is increasing by a lesser rate than revs...meaning torque will decrease.

as an aside, the torque readout on a dyno (especially on an auto) is usually fairly meaningless....because its measuring your entire drivetrain, not just the engine. You'll never get the figures quoted from the factory, and with an auto the torque converter often multiplies torque...making it even less useful in any comparison...

[djr81]

  pixel8r said:

...and with an auto the torque converter often multiplies torque...

Really? Wow.

Edited December 10, 2009 by djr81

[mad082]

that isn't entirely true. in fact i would say that the opposite happens. the torque converter basically has the same affect as a slipping clutch. the revs of the engine are faster than the gearbox is spinning. this is why most auto cars these days have lock up torque converters which basically put it on par with a manual.

[djr81]

  mad082 said:

that isn't entirely true. in fact i would say that the opposite happens. the torque converter basically has the same affect as a slipping clutch. the revs of the engine are faster than the gearbox is spinning. this is why most auto cars these days have lock up torque converters which basically put it on par with a manual.

No it doesn't.

A slipping clutch does so because it is failing to transmit the torque of the engine.

A torque converter works to increase the torque available at the back wheels by letting the motor develop more revs, power & torque and then transmitting it.

Lock up autos are used because once the motor revs beyond about a couple thousand rpm you are better off having it all locked up.

[mad082]

but a torque converter doesn't transmit the torque to the back wheels. if they did then automatics would be dramatically quicker than manuals but they aren't, even once you take into account the different gear ratios that autos have.

[Sarumatix]

You don't think the reason why the majority of really fast drag cars are auto might be somehow related to this . I just got my auto GTS-t dynod and my first question was why does the power shoot up so fast then level out then start looking like a manual. Torque Converter. Auto's are much faster off the line.

[pixel8r]

  djr81 said:

Really? Wow.

Oh lets get all technical about it.....

Autos do generally have a quite inflated torque readout on a dyno and this value is usually completely meaningless unless the dyno is set up with all the parameters specific to that car's gearing etc (which is never going to be the case).

As far as "multiplying torque" what I meant was - when taking off from a standing start, ie where engine speed is much higher than the transmission speed, the torque converter actually multiplies the torque of the engine by 2 or 3 times.

http://auto.howstuffworks.com/auto-parts/t...-converter4.htm