Q&A Forum
Hi, bought this system over christmas and have been running it quite succesfully since on an inertia dyno.
Noticed with some vehicles (RWD BMW in particular) I get a spike at the very end of the graph, it doesn't seem consistent, and it doesn't look to be caused by wheelslip as it's always at the very end of the run - just wondering if anyone has any idea to the cause, or seen similar on their own dyno?
image can be found here:
thoughts on a postcard if anyones seen anything similar before - the two runs above were taken back to back with a slightly later start speed
Hi,
It looks like you have turned on the "Enable correction for frictional losses from retardation data", but you do not do a proper retardation run (clutch in, no brake). Could that be right?
You should also reduce your noise reduction setting.
Hi - thanks for the reply - I'll try the reduce noise setting (at 2 current IIRC)
yes I do have frictional loss calculation enabled, but I am conducting the test correctly - get to end of the run, clutch down, allow coast down to a stand, stop recording on computer then save.
Mostly the dyno test tests fine, but with certain vehicles its a persistent problem. I might be wrong on that but the last two BMW's I've had have been particularly bad.
The dyno only sees ambient atmospheric conditions and a frequency signal, so its an odd one to me as there's not much opportunity for disturbance without actually altering the roller speed
Noise reduction of 2 is ok.
Then it is probably that you stop the run before the brake is off. Try the "Coast" button (space) at the same time you let go the throttle or wait a bit longer before letting go the throttle.
Had same problem before:
with the latest versión, it's supposed it help a bit but i think it's all about press clutch before brakes get off, anyway not sure if this could be improve it a big more yet ,let say a small box telling you press clutch in 3...2..1 ,etc. what's time of ramp you have configured? that may help a bit too.
Hi thanks for suggestiom, I don't have the latest software yet but my soft isn't that old (i.e its from 2 months ago)
thanks for your link, your screenshots don't show but i think we describe similar problem
my dyno is inerta (for now) so i can't hold, but I have tried sitting on the limiter for a few seconds at the end of the pull to allow for more sampling to take place, this has had no effect.
Unfortunately it'l be a few days before i get another suitable RWD in for testing, I tested my own Peugeot 308 earlier and the problem did not appear
So if you do not have a brake, then the issue has to be that the retardation run was not done with a completely free wheeling coasting in the beginning. Can you post the .csv file of the run? If you Right click and choose "Set scale to default" then you will see also the negative part of the curve. Alternatively check out RPM vs time in the time tab to see what's going on.
What sort of RPM is the drum turning.
Are the both the pick up and trigger wheel perfectly secure. Im thinking its not the car thats doing it but vibrations.
Hi admin ill try and trawl up the dyno run and see what the losses are. forgot to do that!
@bmgjet - we did have frame vibration problems late last year and I rebuilt part of the dyno to absorb these better. the sensor is fixed rigidly, and whilst technically a vibration could cause it to move I can't see it plausibly affecting the air gap by much - but what do I know! Because the noise at the end of the run is positive, it would insinuate the sensor is seeing more samples or something.
The strange thing is, this genuinely doesn't effect most cars - so it isnt a major issue, most I put on are light low powered fwd vehicles and its flawless and a lovely system to use.
Thanks everyone for all your pointers