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I know Mazda have trouble reading dyno charts but so am I.

How do you convert the torque from a dyno chart to something more meaniful?

For example, my car (NB8B) made 3830nm @ 120kmh in 4th gear. It made 127kw at the same engine revs.

Can anyone translate that into something more meaningful?, somewhere around 280nm?

Garry wrote:my car (NB8B) made 3830nm @ 120kmh in 4th gear.

3830rpm?

kW = (Nm x rpm) / 9550

so 127kW @ 3830rpm = 316.7Nm

3830nm Locutus, not rpm. I'm not sure how many rpm as the X axis on the chart is in km/h. I guess what I'm after is the torque at the engine, not at the wheels. Mazda claimed 280nm for the SP. Basically I want to know if my car has more or less than that. (and it needs to make more than 320nm to beat rjastras PoLo )

Though your number sounds about right. Assuming it went to redline (7000rpm) the peak torque occurs a bit over half way along the x-axis.

General calculation used

Torque [Nm] = 9549 x Power [kW] / Revs [rpm]

However,

Trying to compare manufacturer measured crankshaft or engine torque with a rear wheel reading, can be somewhat ambigious. Dyno a car in second gear, its got 500Nm, third gear 400Nm, fourth gear 300Nm. Change diff gears and the torque changes again...so whats it got?

Dyno dynamics has a derived torque function, independant of gearing Nm figures in 2nd, 3rd or 4th should be indentical. It's upto the operator to use derived torque when the car is put onto the rollers.

Garry wrote:3830nm Locutus, not rpm. I'm not sure how many rpm as the X axis on the chart is in km/h. I guess what I'm after is the torque at the engine, not at the wheels. Mazda claimed 280nm for the SP. Basically I want to know if my car has more or less than that. (and it needs to make more than 320nm to beat rjastras PoLo )

Though your number sounds about right. Assuming it went to redline (7000rpm) the peak torque occurs a bit over half way along the x-axis.

ahh i see.

i believe 4th gear has a 1:1 ratio for all standard mx5 gearboxes so i guess the the formula would then be:
(torque @ engine) = (torque @ wheels) * [(tyre radius) / 1000] / diff ratio

4th gear ratio in a NB8B 6 speed is 1.257 and the diff ratio is 3.636 according to the Mazda Aus website.

But thanks for that guys. If there really is a 30% driveline loss then my car has more torque than rjastra's PoLo and I win! Thats all that mattered.

Garry wrote:3830nm Locutus, not rpm. I'm not sure how many rpm as the X axis on the chart is in km/h. I guess what I'm after is the torque at the engine, not at the wheels. Mazda claimed 280nm for the SP. Basically I want to know if my car has more or less than that. (and it needs to make more than 320nm to beat rjastras PoLo )

Though your number sounds about right. Assuming it went to redline (7000rpm) the peak torque occurs a bit over half way along the x-axis.

Looking at the specifications of 2wd and 4wd dynodynamics rollers, max torque occurs at 3500rpm. Road tractive effort is in newtons (N) which is what the 3830 is and newton meters (Nm) is used to measure engine torque.

So how do you convert newtons to newton meters?

Garry wrote:So how do you convert newtons to newton meters?

I dont believe its just a matter of converting (N) to (Nm) when you converting road tractive effort to engine torque. There must be another conversion factor as well, I guess if that calculation was freely available engine dyno sales wouldnt be so great.

According to Mainline, you can work out road tractive effort from (N) to (Nm) however you still need to consider gearing and slight roller loss across the tyre.

Muliplying the Tractive effort by 0.1085, which is the conversion from Newtons (tractive effort, or Motive Force) to Newton Metres on a Roller of a Diameter of 217mm, however this does consider gearing and slight roller loss over the tyre, this is where derived torque function plays a roll

it's all to hard I'll just be happy to look at the pretty picture