Q&A Forum
Hi Guys, Have finally got my chassis dyno running with your dyno.
I have a question. Todays car read very low compared to what i thought it should have been.
I keeped going and made another 50 rwkw, however, wasnt until after i i looked at the PID control and relised it was flat lined compared to past cars.
Nothings really changed. Same thing i have done for each car.
Make new folder, set gear ratio, hold brake at set rpm loads to get fuel in spec, then do a wot pull to get base line.
This one was probably 50 rwkw lower then i thought it should be.
Why would the PID control be flat lined?
Cant seem to find how to add pictures
TIA ! Trev
Here is how to see what happened:
- Create the Brake setup analysis tab if you don't have it already
- Go to that tab and check the Engine RPM vs Target RPM. In the same graph you will see the Brake %. If Engine RPM is below the Target RPM then the brake will be off.
Adjust the sweep time if you want the brake to be engaged (slower sweep), however you shall get the same power whether the sweep is fast or slow, so if the power is too low when the brake is off, then your Moment of Inertia setting is likely too low. There are some tips on how to measure the MOI in the software manual.
Thank you for your swift reply, I have just looked at that tab and you are right, the brake is off. The target RPM seems to be 1500rpm, the log starts at 2000rpm, brake is set to 0 the entire time. But i do recall each run the brake holding RPM at 2000 for 2 seconds before ramp run starts.
I have logs of the run in HPTuners and the your dyno run. Is it possible its holding RPM then letting the brake go?
I Havent done anything different from what im normally doing, but i am new to the software to. Unless im missing a crucial procedure each time i load a new car?
If you use Power Sweep and have a hold time of 2 seconds, then it will hold that RPM for 2 seconds using the brake, then after 2 seconds, the sweep starts. Recording also starts after 2 seconds.
You can send me the csv file and I can take a look if you want. Send to jostein@yourdyno.com
Thanks Jostein, I think my MOI maybe out a little, I will further calibrate. However, i did get to the bottom of this. All a steep learning curve!
It turns out that whilst nothing had really changed, I had been running some higher horsepower cars before this issue popped up, my ramp rate was set at 500rpm/s. I have quite heavy rollers (MOI between 23-25, though this may still not quite be correct if it doesn’t equal the braked kw value and the non brakes kw value)
but what I found was by dropping the ramp rate to 400rpm/s the brake was applying again after the 2 second hold on the slower cars as they must not have been powerful enough to overcome the inertia of the rollers when set higher! So thanks for leading me towards the brake setup analysis table!
Yes, this makes sense. If the Engine RPM is below the Target RPM, then the brake will be off. In this case it will run as an Inertia dyno which, if the MOI is correct, still gives correct power/torque readings.