SAS Dyno setup, result and characteristics thread

[ginganinja]

Out of interest, do rolling road dynos read higher torque than the hub dynos? Just seems a lot of dyno sheets i've seen done on rolling road have quite high torque numbers.

Edited October 1, 2020 by ginganinja

[gotasuby]

15 hours ago, ginganinja said:

Out of interest, do rolling road dynos read higher torque than the hub dynos? Just seems a lot of dyno sheets i've seen done on rolling road have quite high torque numbers.

Some rolling roads do read a higher torque reading wgich I guess is measured axle torque. Our dyno does that too but then decides it by diff and gearbox ratio to give engine torque 

[boon]

To accurately determine the torque on a rolling road requires things like accurately knowing the diameter of the tyre, because you are effectively "gearing" the power transmission to the roller.

 

For tuning purposes, where you only care about increase/decrease based on changes to the tune, it's not an issue. But it highlights the pointlessness of comparing dyno sheets from different dynos.

[Andy_Mac]

4 hours ago, gotasuby said:

Some rolling roads do read a higher torque reading wgich I guess is measured axle torque. Our dyno does that too but then decides it by diff and gearbox ratio to give engine torque 

 

Do all dynapack dyno’s do it that way? So you’d be essentially getting wheel kw and flywheel torque on the readout?

[gotasuby]

23 hours ago, Andy_Mac said:

 

Do all dynapack dyno’s do it that way? So you’d be essentially getting wheel kw and flywheel torque on the readout?

Yes correct but remember engine torque measured at the axles after all drive train loss so same engine on a engine dyno will read higher 

[Andy_Mac]

23 minutes ago, gotasuby said:

Yes correct but remember engine torque measured at the axles after all drive train loss so same engine on a engine dyno will read higher 

 

Yeah I know wheel power will be considerably lower than flywheel/engine power. Just never considered they would apply connection factors to give engine torque as the standard torque figure

[gotasuby]

Not a correction factor. Just means if you do it in 5th and sync rpm to hub speed then do 4th and recalibrate ratio it will read the same. Otherwise you will get different torque readings in each gear

[Andy_Mac]

2 hours ago, gotasuby said:

Not a correction factor. Just means if you do it in 5th and sync rpm to hub speed then do 4th and recalibrate ratio it will read the same. Otherwise you will get different torque readings in each gear

 

Ahh I get ya now, so it's giving engine torque from the axles to bypass any multiplications from gear/diff ratios but doesn't attempt to give any guesstimated drivetrain loss factor to give a true figure at the engine

[gotasuby]

Correct people always ask hp at the engine. And it really doesn't matter. A 300hp car at the wheels could make 320 or 500hp at the engine all that matter is what comes out the axles