Easy way to work out a more sensible torque fig from the crazy 'derived' dyno results

[kahlnz]

I know loads of people dislike the crazy 'derived' rear wheel torque figures that we get on dyno results so here's a way to make sense of it...

1. find the rear wheel hp figure at 5,250rpm (i.e. 245rwkw/329rwhp)
2. given hp=ft lb (torque) at this rev, 5,250rpm, you know you have 329 ft lb
3. find the 'derived' rear wheel torque figure at 5,250rpm (i.e. 735nm/545 ft lb)
4. divide the figure in step 3, 545 ft lb by figure from step 2, 329 ft lb and you will get the derived factor, in this case 545/329=1.66 (this is the fixed multiplication factor the derived figures use when considering final drive gear, converter slip, dyno roller diameter, etc)
5. simply divide all of your torque results by 1.66 (use the figure you got in step 4) and it'll give you a way more sensible torque figure.

After I performance tuned my VE SSV and added an OTR my dyno results were 244rwkw/800nm (derived, at the wheels). Although these are true, the torque figure never made sense and I couldn't think about it practically but when you apply the method above you get 244rwkw/478nm which looks spot on. test it one step further and factor in a drivetrain loss of 23% (auto) and flywheel figures of 317kw/620nm sound just right when the stock one was 270kw/530nm.

I hope this helps some people to better appreciate their dyno results.

 

[acarmody]

So using this method my car (VX V6 Ecotec) actually makes 207nm of torque, which I will apply the drivetrain loss (your 23%) makes 255nm of torque.

Wish someone would have told me my car will only make an extra 25nm of torque after installing a cam, higher compression, intake, exhaust and various other smaller stuff.

I MUST HAVE GOT RIPPED. Or this method doesn't work. One or the other.

 

[kahlnz]

What is your rwkw and derived rwnm at 5,250rpm? Also what is your peak derived rwnm? Cheers

 

[monkeys437]

Torque = (9880xPower)/(RPM) with torque in Nm and Power in kW.

If you want a real engine torque figure I think the beast estimate is using estimated driveline losses to work out your engine power in kW, then using the above formula.

However what you've come up with seems like a pretty decent estimate too, maybe just over thinking it a bit

 

[acarmody]

What is your rwkw and derived rwnm at 5,250rpm? Also what is your peak derived rwnm? Cheers

Peak torque 350nm.

At 5250rpm, 140rwkw and 320nm

 

[kahlnz]

Sounds like you might be working with dud dyno stats, with the mods you've done I'd expect a fair bit more than 140rwkw anyway. With my calcs, 140rwkw/255nm and peak of 278nm seems to sound right from a ratio perspective so maybe the dyno was well under, is it auto or manual? diff or wheel mods?

 

[Not_An_Abba_Fan]

You are working it backwards. A dyno measures torque, real torque, not derived, not estimated, not formulized (is that even a word?) then it applies a formula to obtain a power figure. Power is the estimate. Torque is measured. All engines will make their peak torque at different RPM, and that will even change in different gears. To have a true benchmark, torque should be measured at direct 1:1 drive, so whichever gears gives 1:1 drive then that is the gear to measure torque in. Then it will give a calculated power figure. The power figure is the one that is "derived" or "calculated", not the torque.

 

[Bomber R8]

You are working it backwards. A dyno measures torque, real torque, not derived, not estimated, not formulized (is that even a word?) then it applies a formula to obtain a power figure. Power is the estimate. Torque is measured. All engines will make their peak torque at different RPM, and that will even change in different gears. To have a true benchmark, torque should be measured at direct 1:1 drive, so whichever gears gives 1:1 drive then that is the gear to measure torque in. Then it will give a calculated power figure. The power figure is the one that is "derived" or "calculated", not the torque.

Exactly. Very well said!

 

[kahlnz]

thanks for that Not_An_Abba_Fan,

so basically, just worry about what's happening at the rear wheel? so my dyno results of 328kw and 910nm at the wheels is all I need to worry about? and the 1/4 mile results. I guess I was overanalysing it so I could get an idea of a nm rating at the flywheel but who cares?! What's your thoughts on dyno results for later model autos where you can't get a 1:1 drive? my results were measured in 4th gear (1.15:1).

Cheers

 

[Not_An_Abba_Fan]

You got 910nm of torque? What was your RPM? I worked it out to about 3500rpm, you must have a big engine to produce that much torque that low in the revs and only get 328kW.

Or did the dyno give you "motive effort"?