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

[kahlnz]

yeah 900+nm, it's from 4,500-5,500rpm, sounds high hence why I was initially determined to work this backwards to a more 'realistic' figure which I thought (using my formula I posted originally) was about 545rwnm. The dyno was a DynoTorque and the tuner said this is the true torque measured through the wheels, no other way to measure it. Still confusing but they are the experts so won't argue with them, now I know why all these turbo's etc can pull 1500+nm of torque through a very wide rev range.

 

[Not_An_Abba_Fan]

If you got 910 nm of torque at 4500rpm, you will have 780kW. At 5500 rpm it is 950kW. Something is wrong. Or you were in 2nd gear.

Even 545 nm is 466 kW.

 

[kahlnz]

I agree these are misleading results which is why I originally started this thread. with the calculations I stated at the beginning you can get a better idea of real torque versus the torque exerted against the dyno rollers (910nm). The formula I proposed in this thread estimates my peak not to be 910nm but rather 545rwnm and this is fairly closely confirmed with the standard metric formula where power (kw) = torque (nm) x RPM / 9549. This gives an answer of 525rwnm. Work this back through a 28% DT loss and you get a flywheel result of 455kw/730nm (610hp/540ft lb).

This is all within logic given it started out with flywheel figures of 270kw/530nm. OTR and Tune gave it 340kw/630nm then Cam, PnP Heads, Headers and Exhaust gave it 455kw/730nm.

 

[Not_An_Abba_Fan]

The torque exerted against the dyno IS real torque. Thats how a dyno works, it measures rear wheel torque exerted on the rollers. The in built software takes into account the roller diameter, as long as the inputs are accurate, eg tyre size, which gear it runs in, tyre pressure etc, then the result is the torque you have at your rear wheels. Then the software converts that figure to power.

Generally, what ever the kW figure calculated for the rear wheels, is about your HP figure at the flywheel.

There should be nothing misleading about a dyno's torque readout. There are other ways dyno's measure though, "tractive effort" or "motive effort" are one, but the main thing to remember is that a dyno is a tuning tool, software has been built in to calculate power, but all that is is wank factor. But if it's a number you need to brag about, then all those that you are comparing it to, should all get measured on the same dyno, on the same day, by the same operator, as each dyno will give different results as consistency is the key for "shoot outs".

 

[Tsunamix]

Yeah - few glaring holes in stuff above -

Abba is that the right way round ? 280HP at rear wheels for me, thats 209kW at the wheels. I reckon I got a damn site more than 209HP at the flywheel. Thats only 177kW

The other way round is still misleading - 280hp at wheels may be closer to 280kW at the engine.

i think everyone is making assumptions on losses scaling. They don't.

Percentages can not work in calculating losses. Percentiles are proportional, lossess are fixed plus a small amount of variation due to things like oil hysteresis etc, Friction losses remain roughly fixed. Your alternator may take 2HP to drive on a 200kW engine. If you use the same alternator on a 300HP engine it still takes 2HP to drive it - not 1% which is 3HP.

Follow me ?

ANyway the only way you can use % is as a cross check for relative losses.

Stock Ecotec
147kW Flywheel
Approx 119 at wheels
Losses = 28Kw (19%)

Flywheel Torque = 304Nm at 3600
Rear wheel derived torque = 559 at 3600, which gives a calculated flywheel equivalent of 242Nm or losses of 62Nm or 20.4%.

Losses are relatively close so the numbers are relatively accurate.

Looking at my Dyno results - attached, you can see that the RWKW = 209 (or 280HP) my driveline looses will be similair to stock, maybe a little less as gearbox is modified, so expecting losses of 25kW, my engine kW islikeley to be 234kw.

Apply same losses calc to torque, remembering 3,7 gear ratio, means flywheel equivalent torque, before losses is about 487Nm. (1351 /3, * 4 , / 3.7). Add about 55nM torque for losses and actual engine torque is likeley to be 542Nm.

I Estimate my engine results as 234kW and peak torque of 540Nm. Seems pretty fair really.

 

[Not_An_Abba_Fan]

I'd say your readout is pumped up due to the fact that it was 3rd gear with 3.7's. 3rd gear in a VT is not 1:1. What you have is an accurate measure of torque in 3rd gear, do it again in 4th and see what it reads. It will be different in every gear, but for a true comparison, if you were to quote your figures showing your car's output, then it really needs to be done at 1:1.

I can chuck my 3.5L Rangie on a dyno, put it in low range and 2nd gear, I bet it will pull huge torque figures.

But that aside, using the dyno as a tuning tool, it doesn't really matter what gear you are in, you just need to load the engine up and see how it performs.

And yes, sorry, other way around, whatever the HP at the wheels is roughly what the kW are at the flywheel.

 

[Decicrate]

I'd say your readout is pumped up due to the fact that it was 3rd gear with 3.7's. 3rd gear in a VT is not 1:1. What you have is an accurate measure of torque in 3rd gear, do it again in 4th and see what it reads. It will be different in every gear, but for a true comparison, if you were to quote your figures showing your car's output, then it really needs to be done at 1:1.

I can chuck my 3.5L Rangie on a dyno, put it in low range and 2nd gear, I bet it will pull huge torque figures.

But that aside, using the dyno as a tuning tool, it doesn't really matter what gear you are in, you just need to load the engine up and see how it performs.

And yes, sorry, other way around, whatever the HP at the wheels is roughly what the kW are at the flywheel.

Everything I have read on a 4l60e shows that 3rd gear is 1:1 ratio and forth is 0.696:1. Straight out of the Holden workshop manual it states the 3rd gear ratio is 1:1.

 

[Not_An_Abba_Fan]

Am assuming his is manual, but if it's auto, then all good.

 

[Decicrate]

It is an auto.

 

[Tsunamix]

I have seen a heap of dyno results in the dyno thread that aren't run in a 1:1 ratio.

Luckily i gone my work done by someone with a brain - its an auto 4L60E.

My numbers are probably low on the power side, but if they are low on the power side they are also low on the torque side. I only claim the same losses as a stock engine

Maybe - just maybe I have a bit more.