Road dyno calculations

[moose]

Hello,

I hope somebody here can point me in the right direction. I am trying to put together some software to read TARI (and possibly other dataloggers) output and create dyno charts based on that input. I have done some reading, but haven't been able to really put it all together as far as the math involved. Does anybody have any recommendation for where I could find the equations needed to calculate everything based on rpm, velocity, time, gear ratios, drag coefficient etc..?

Thanks!

[calvinc]

i had a guy contact me a while back to add this feature to ecuExplorer. i had to give him a log file with just the engine speed from 2000RPM to redline. additional information required is:
- tyre size
- ambient temperature
- atmospheric pressure
- car weight
- passenger weight
- fuel level
- gear used during run

i'll contact him again and see if i can add this to the app.

calvin.

[qoncept]

I don't have the time to look for it now, but play around with google a bit -- I found quite a bit of info and the formulas are readily available. I think about.com might have had it.

I'm not sure how much accuracy you're going for, but it seems to me most of it can be estimated and give accurate enough results. Also, wouldn't the gear be irrelevant? The way I see it, all you'd need in your log is RPM and time (atmospheric pressure for more accurate results) and you should be able to calculate from there.

[Freon]

You can do some searching on Google, and try Google Groups in particular.

Here is a worksheet I created while working on my last car with SMT-6 logs. The log quality and time domain isn't very good, but I think it generally works. Checkout "Sheet 1" in this file:

http://freon.shackspace.com/ecu%20and%2 ... sheet2.xls

There are probably a few ways to do it. Speed vs. time is probably your best bet for actually calculating power, then go back and plot it against RPM. Conversion from HP to Torque and vice versa is trivial.

I would not suggest trying to compensate for drag. Just try to calculate actual net work done. All you need is the mass of the object, and a log of speed vs. time.

You can also use RPM vs. time, and calculate speed using known gear ratios, and knowing which gear you are in. But you are still using speed vs. time.

From speed vs. time, you calculate speed delta (acceleration), and with a known acceleration rate and known object mass you calculate power.

Hope that helps.

[Tony555]

It is me the guy that Calvin mentionned.
Here's a result of a member of my Subaru Club



I have done this graph with calculations similar to what Freon say's.

Here's the difference between my calculation and the Deltadash one's.


Mine seems optimistic but smoother. One day I'll compare real dyno log with road dyno to compensate for errors.

You must be aware that this type of road dyno is just to compare two setups. You will then be able to ''see'' the difference in the power curve.

BTW Calvin, you've got mail!