Physics Lesson – Calculating Torque and Power From Datalogs


I did some self-tuning on the Evo but I never did re-dyno it.  However, I do have datalogs!  You can see the big torque and power gain from ~4500rpm to 7000rpm I got from my retune.

Of course, I’m not the first person to come up with this idea.  A guy named Brad Barnhill created software called Virtual Dyno.  It has a library of cars already loaded up with weights, drag coefficients, frontal area, and gearing so that you don’t have to look it up.  You can even do SAE correction on your dyno plot to take into account varying ambient conditions.  It can take datalogs from many different software applications used for datalogging cars of all makes.


This is a plot using Virtual Dyno with a smoothing level of 1.  


Here is a comparison of my spreadsheet dyno compared to the result from Virtual Dyno with the smoothing level set to 2.  I think my spreadsheet looks pretty decent considering the minimal data processing.

Basic physics and math can let you calculate cool things when it comes to cars.  Datalogging only time and engine rpm allowed me to calculate power and torque relatively accurately with minimal data processing.  Of course, simulations are only as good as your inputs, so the accuracy can be thrown off by the inputs of weight, coefficient of drag, frontal area value, and weather conditions.  You can make your own spreadsheet, Matlab GUI, or you can just download Virtual Dyno which I’m sure has better developed algorithms for smoothing out the data than I came up with in a few minutes. Remember, these are just tools just like a chassis dyno and minimizing variation is the key to making these tools useful.  Physics is cool, stay in school.


    1. You are absolutely correct, thanks for catching that! Should have been: Force = Torque / Radius

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