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Fun with data acquisition (060mph, 0100mph, 1/4 mile, acceleration rates, etc)


06142007, 05:19 PM  #1 
Lieutenant Colonel

Fun with data acquisition (060mph, 0100mph, 1/4 mile, acceleration rates, etc)
For geeks only:
Those of you with PROcede (or maybe even XEDE) can take heart in the fact that you can get some quite accurate performance "metrics" using the data acquisition capabilities of the system. By that, I don't mean that you can get accurate HP/Torque numbers. Rather, I mean that just by gathering the following data channels during a hard acceleration run: RPM Time MAP and combining it with the gear ratios (from bmwusa.com), you can determine the following: 1) 0xxx MPH times (060, 0100, what have you) 2) xxx foot times (60ft, 1320ft, etc.) 3) Boost 4) Nearly instantaneous acceleration rates (the software records data at 0.040.05 second intervals) From (4), I calculated the RPM/Second rate of increase to see where acceleration is strongest and where it tails off. This helps me determine the appropriate shift points. The 1/4 mile times calculated from the acquired data was compared against a drag run and it was SPOT on. I'm in a bit of a hurry, but this should plant the seed in your mind  let me know if you can't figure out the actual steps to do it.. 
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06152007, 10:36 AM  #2 
Major

I'm too stupid to figure out this riddle. What are the numbers you came up with?
__________________
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06152007, 11:24 AM  #3  
Lieutenant Colonel

Quote:
Here are some more steps: 1) Take the MAP, Time and RPM readings using the Procede software while doing a few hard acceleration runs. 2) Open the data in Excel, figure out your shift points (right before MAP spike, through the boost decline, right up to when it starts going up again). A further advantage is you can precisely calculate your shift times. 3) Apply the RPM to MPH factors for various gears to the appropriate data points to determine your speed during the run. For 1st, it's 0.005692308 mph per RPM For 2nd, it's 0.009692308 For 3rd, it's 0.014923077 For 4th, it's 0.019692308 4) Create a column that shows your "time from start of run" by subtracting each data point's time from the start time. 5) Calculate feet covered during each data point interval by taking MPH at that data point, divide by 60, divide by 60 and multiply by 5280. That gives you feet per second. Then multiply that by the time difference between that data point and the one before it. 6) Total distance is determined by creating a running sum of the feet covered. 7) If you want to get fancy, you can calculate the rate of MPH/Min, which will show you precisely where your acceleration is the strongest. Create a graph using Excel, (RPM vs. whatever you want) and then I would recommend adding a moving average trendline to smooth out the data. From the chart and the data table, you can determine 60ft times, 1320ft times, trap speed, 060, 0100, whatever you want. Disclaimer: The data might be slightly (we're talking 0.01 seconds) optimistic because it assumes all rpm increases result in forward motion, which is obviously not true when you spin your tires. But luckily tire spinning typically occurs at low speed, so the data skewing isn't too bad. As I said, my "software derived" 1/4 mile time matched the dragstrip time precisely. 

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