dyno test

[Nitesh]

I know this would sound lame to many and the post may be up for a lot of bashing but we have suddenly been alloted dyno time at a local car manufacurer's facility. We have never used a dyno before and though we would be assisted by their operator, we have absolutely no idea of what to do there. Any help or reference to some reading material would be greatly appreciated.

[Nitesh]

I know this would sound lame to many and the post may be up for a lot of bashing but we have suddenly been alloted dyno time at a local car manufacurer's facility. We have never used a dyno before and though we would be assisted by their operator, we have absolutely no idea of what to do there. Any help or reference to some reading material would be greatly appreciated.

[Dallas Blake]

I'm assuming that the manufacturer is letting you use a chassis dyno and not an engine dyno. First question is do you guys have a base fuel and spark map yet? what ECU are you using?

If you already have a very rough map (enough to get it running) then the process comes in two parts, cell by cell tuning and transient testing. Start off by holding specific RPM and load (be it TPS if you use alpha-N or MAP if you use speed/density) called your break points, at each of these points monitor your AFR and adjust your fuel in your VE table until you get the AFR you want/maximum torque (there is an entire balance between fuel consumption and power production that I wont get into here). At each of these break points adjust your spark advance until you reach maximum torque, back off the advance until your torque starts to fall, this point is called minimum best timing, it is the minimum spark advance that gives maximum torque. Go through all your highest load points for each RPM and adjust fuel and spark, move downwards in load and tune those cells the same way. Once you have all these individual cells tuned for maximum torque go on and so some tranient tests. I've never done these on a chassis dyno as we use an engine dyno for our tuning and our control software has programmable transient tests. Transient tests are just means of measuring your AFR,torque, EGT Manifold pressures etc. during acceleration. from this you will be able to adjust your fuel enrichments for manifold pressure and tps rate of change as well as decelleration fuel cuts. Once you have these compensations accounted for and your AFR remains stable through transient tests then its time to start analyzing your curve and see how you may want to change your intake/exhaust design to better suited your original requirements. This is all just a very basic outline of what to do, dyno tuning takes time to learn and experience to understand the effect that certain changes will have on your engines operation

I hope this somewhat made sense, if it doesnt then let me know, I've been studying for 3 weeks solid and its starting to get to me

[Nitesh]

that definitely made a lot of sense, Thanks for all the info. The only problem is that if i hold the load with the TPS, and vary the fuel, the rpm would keep changing. to hold the rpm, i'll have to vary the throttle. how do i hold both the rpm and load and still vary the fuel/spark??
we're using PE and will be starting with the default map file they have provided.
The manufacturer is giving us an engine dyno. Due to the low dyno time available, we would be coupling it with the sprocket of the engine and make backward calculations
How do we work on the temperature compensations, as temp is a major variation when working in India and in UK.

[jdstuff]

Google SAE standards (for example SAE J1349 JUN90) for things such as "correction factors", and you should have decent results. You'll have to take some ambient condition measurements in order to calculate any type of horsepower correction factor, so be sure to measure more than just temperature. Here's one such horsepower correction factor that I use frequently:

cf = 1.18*((990/Pda)*((Ta+273)/298)^0.5)-0.18

Where cf = corrction factor (unitless)
Ta = ambient temperature (deg C)
Pda = pressure from dry air (mb)

I'll let you figure out what you need in order to get Pda. http://fsae.com/groupee_common/emoticons/icon_wink.gif Happy tuning!

[Dallas Blake]

That is true, if you vary fuel you will have changing RPM for a constant load, its just a matter of adjusting throttle and load control in order to get to the cell you want to tune. Once you get in there and start adjusting it will make much more sense. jdstuff touched on something I totally forgot about you will need to work with correction factors. depending on the control system the dyno will have this can be easy or hard. We use a superflow and the accompanying winddyn software and we need to input things such as fuel specific gravity for the computer to make corrections and then the dyno sensors for teperature, humidity, pressure etc take care of the rest. One thing that is extremely important is figuring out how to deal with inertial losses on an engine dyno. You are going to be loosing a significant amount of torque during acceleration on transient tests depending how large your dyno is and how your absorber valve is set. Check out my engine journal on our website to see how I went about correcting for this.

and jdstuff, eww figuring out dry air pressure. I just finished our applied thermodynamics II course including phychrometrics and Im so glad to be finished with that sort of analysis and the ridiculous phychrometrics chart