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Dynapack 2000 incorrect torque figure

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Hi all,

We have a dynapack 2000 which is giving incorrect torque figures, although the power figures are what we would expect.

I have calculated that the torque is out by a factor of ~13. I have attached a spreadsheet of the data from the dyno along with a calculated torque figure based off the power. The engine on the dyno for this was a KTM500 with a turbo. Due to the low inertia of the drivetrain we are finding that we have to run it in 2nd, we are setting the correct ratio to ensure dyno rpm reading is the same as the engine.

All and any help would be appreciated. Dynapack do not want to get back to me. :(

Spreadsheet not showing.

It calculates power from torque applied to the roller and the roller speed - not sure how it can be wrong?

Why are you 'calculating' rather than using a spark plug pickup - and exactly what are your calculation formulae?

Not sure why you are using a low gear - the inertial error is reduced in higher gears?

Gord -- A dynapack is a hub-mounted dyno. There are no rollers. Since there is no slip, it is perfectly acceptable to determine engine speed from the hub speed -- the Dynapack 2000 doesn't even have a separate RPM input.

Ryan - The dynapack can display several different torque values, my guess is that you are looking at hub torque and your total gear ratio is close to 13:1. Use the channel selection menus to choose the torque that represents the engine torque.

Thanks David final gear ratio is 13.1, that sounds correct, I will have another look. Hopefully the speadsheet is now attached.

Gord - Due to the low inertia of the driveline, the driveline comes to a stop if you try to change gears and it is quite difficult to take off in 4th.

We are calculating torque from the hp figures as the current torque appears to be wrong.

Power (kW)*9.5488/Speed(RPMM) = Torque (N.m)

Attached Files

You can display torque at the hubs which will look ridiculous because it's multiplied by your current gear ratio and final drive ratio, or you can display flywheel torque which removes the gear multiplication out of the equation and then multiplies out by the TCF value to give a theoretical flywheel value.

Doh, shows what happens with lack of sleep - sure hope it isn't early Alzheimers. I was thinking a bike, on a roller - this a Formula Student type car?

As has been said, hub type chassis gives the torque at the hubs, and has to be divided by the overall gear ratio for engine torque estimate.

IIRC, the correct correction factor for N.m and kW is 9880 - it is an easy calculation, if you want to check it. NOTE, dynos and conversions use kg.m and this can catch folks out. heck they're all on-line so should be albe to just enter values into one of those conversion formulae.

Haha at least it was an easy one to solve! Thanks guys!

Gord - Yeah FSAE car, I have attached a picture of our engine bay.

Attached Files

Cool, been following them for years on RCE - they have had some very good articles over the years, from back when it was Formula First.

Is this a university/college engineering class thing or a dedicated motorsport 'academy'?