how do i read my dyno chart?

[xt falcon]

as the subject says. i understand the hp but not the torque, it has the vertical scale that says lb but how would i translate that to nm or ft-lb.
thanks Aaron

 

[xctasy]

Man the crap that comes out of so-called expert chassis dynos is just unbelivable.

I've seen kph, km/h, lb, lb-ft, uncorrected results, and readings taken in third gear with the torque multiplation factors shoved in, KW where others have hp, some factor a third loss for the drive train, others do funny things with the temperature corrections. It's all designed to confuse a poor newbie into just nodding his head, and wondering WTF he's just had done to him.

Sorry to rant.

Apply the following steps, and it'll work out. Most dyno guys have the program set up to give the customer what he wants, so I may be complicating things. Just give your dyno guy a copy of this and get him to sort it out. You spend the gold, you get the info.


Any way, some basics. Engine dynos don't measure power, they measure twisting force, which is called torque. If you grabed a foot long sidcrome shifter, and hung 269 pounds off it, you'd produce as much torque as an XR6 Falcon! Thats what lb-ft, or ft-lb, or pound-foot is. Just a measure of how hard an engine can turn a calibrated brake drum. Power is a measure of how quickly the torque is produced. It's always calculated from the torque figure.

Any time you add a diff or a reduction gear like 1st, second or third in a four or five speed gearbox, you multiply torque. With a 3.45:1 diff, and a 1.3:1 third gear, an XR6 would give around:-

Step 1: 954 lb-ft at the rollers. That would be at around 3500 rpm, or at about 92 km/h or 57 mph. Then they take the 954 lb-ft figure,

Step 2: divide it by 3.45 and 1.3, and that gives 212 lb-ft.

Step 3: With a T5 and a stock XR6 tyre is around 26.4% drive train loss, so that gives us 212*1.264=269 lb-ft.

Step 4: Then the whole range of torque figures are taken from 1500 rpm to 5500 rpm, at 250 rpm intervals at a set rate. Five runs should be taken, then averaged, otherwise you get bulls*** readings. You do the math from step 1 to step 3, and you apply the formula torque*rpm all over 5252. This gives you the rear wheel hp power.

Step 5: Then a horspower correction is made for humidtiy, barometric pressure.

If you have metrics, then you need to know that 269 lb-ft is 364 Newton Meters (Nm). Step 1 may yield 1290 Nm, but just calculate thru to Step 3 is the same way, but you then use Nm*rpm all over 9552 to get kW's, then apply the power correction.

An early manual XR6 has around 175 hp at the wheels, from an engine rated at 164 Kilowatts or so at around 5000 rpm. Thats 220 hp at the flywheel. 269 lb-ft (364 Nm) @ 3500 rpm or so.

If it'd make it simpler, just read off the figures for power and torque at the following rpms, and plot them on a scrap of paper. We won't embaress you!

1500 rpm_xxx lb-ft,_= xxx bhp
1750 rpm_xxx lb-ft,_= xxx bhp
2000 rpm_xxx lb-ft,_= xxx bhp
2250 rpm_xxx lb-ft,_= xxx bhp
2500 rpm_xxx lb-ft,_= xxx bhp
2750 rpm_xxx lb-ft,_= xxx bhp
3000 rpm_xxx lb-ft,_= xxx bhp
3250 rpm_xxx lb-ft,_= xxx bhp
3500 rpm_xxx lb-ft,_= xxx bhp
3750 rpm_xxx lb-ft,_= xxx bhp
4000 rpm_xxx lb-ft,_= xxx bhp
4250 rpm_xxx lb-ft,_= xxx bhp
4500 rpm_xxx lb-ft,_= xxx bhp
4750 rpm_xxx lb-ft,_= xxx bhp
5000 rpm_xxx lb-ft,_= xxx bhp
5250 rpm_xxx lb-ft,_= xxx bhp
5500 rpm_xxx lb-ft,_= xxx bhp